GSM BSC Operation
GSM BSC Operation
STUDENT BOOK
LZT 123 3801 R7A
LZT 123 3801 R7A
© Ericsson 2006
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GSM BSC Operation
DISCLAIMER
This book is a training document and contains simplifications.
Therefore, it must not be considered as a specification of the
system.
The contents of this document are subject to revision without
notice due to ongoing progress in methodology, design and
manufacturing.
Ericsson assumes no legal responsibility for any error or damage
resulting from the usage of this document.
This document is not intended to replace the technical
documentation that was shipped with your system. Always refer to
that technical documentation during operation and maintenance.
© Ericsson 2006
This document was produced by Ericsson.
•
It is used for training purposes only and may not be copied or
reproduced in any manner without the express written consent
of Ericsson.
This Student Book, LZT 123 3801, R7A supports course number
LZU 108 625 .
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Table of Contents
Table of Contents
1
SYSTEM DESCRIPTION...............................................................7
GENERAL INFORMATION ....................................................................9
NETWORK NODES .............................................................................10
NETWORK GPRS/EGPRS NODES.....................................................21
2
CHANNEL CONCEPT .................................................................23
GSM AIR INTERFACE .........................................................................25
GPRS AIR INTERFACE .......................................................................31
HIGH SPEED CIRCUIT SWITCHED DATA .........................................38
CALL SETUP MOBILE TERMINATED CALL .....................................40
MEASUREMENT PROCEDURE..........................................................42
MEASUREMENT REPORT .................................................................46
SYSTEM INFORMATION.....................................................................49
RACH PARAMETERS .........................................................................55
GSM – WCDMA CELL RESELECTION AND HANDOVER.................57
3
BSS CONFIGURATION ..............................................................63
BSC AND TRC HARDWARE OVERVIEW...........................................65
AXE810 BSC / TRC HARDWARE .......................................................71
DEFINITION OF NODE TYPE .............................................................77
NODE TYPE PARAMETERS ...............................................................79
BSC AND TRC SPECIFIC HARDWARE .............................................82
A-INTERFACE .....................................................................................96
A-BIS INTERFACE ............................................................................103
LAPD SIGNALING.............................................................................104
RADIO INTERFACE (UM) SIGNALING LAYER 3 .............................108
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CONNECTION MANAGEMENT (CM) ...............................................109
A-TER INTERFACE ........................................................................... 110
ETC 155 MBIT/S ................................................................................ 111
BSS ARCHITECTURE FOR GPRS ................................................... 118
NEW FEATURE .................................................................................124
MANAGED OBJECTS (MO) ..............................................................127
CONNECTION OF TG, MODEL G12 .................................................131
COMBINING TRANSCEIVER GROUPS IN ONE CELL....................139
FLEXIBLE POSITIONING SUPPORT ...............................................140
4
RADIO NETWORK ....................................................................143
INTRODUCTION ................................................................................145
CELL DATA........................................................................................149
5
PERFORMANCE MEASUREMENT AND SUPERVISION........173
MOBILE TRAFFIC RECORDING (MTR) ...........................................175
CELL TRAFFIC RECORDING (CTR) ................................................178
CHANNEL EVENT RECORDING (CER) ...........................................181
ACTIVE BA-LIST RECORDING ........................................................184
FREQUENCY ALLOCATION SUPPORT (FAS) ................................186
STATISTICS, BASED ON MEASUREMENT RESULTS....................190
REAL TIME EVENT DATA.................................................................192
6
BSS OPERATIONS ...................................................................197
SYSTEM SUPERVISION ...................................................................199
MONTHLY SUPERVISION.................................................................204
BLOCKING SUPERVISION ...............................................................206
SEIZURE SUPERVISION OF LOGICAL CHANNELS....................... 211
CALL PATH TRACING IN THE BSC .................................................216
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CALL PATH TRACING IN THE BSC .................................................216
7
BSC/TRC MAINTENANCE........................................................221
BSC/TRC MAINTENANCE ................................................................223
SRS MAINTENANCE.........................................................................229
SRS CONGESTION SUPERVISION..................................................231
COMMAND ORDERED LOOP TEST ................................................233
8
BTS MAINTENANCE ................................................................235
BTS MAINTENANCE.........................................................................237
BTS ALARM COORDINATION..........................................................243
BRINGING MOs INTO OPERATION .................................................250
FUNCTION CHANGE AND PROGRAM LOAD OF MO ....................252
APPENDIX A .....................................................................................255
FEATURES ........................................................................................257
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1 System Description
Objectives:
Identify the GSM/GPRS/EGPRS system using diagram in
blocks of the identities and descriptive of all the units that
compose the system.
ƒ List the Network Nodes of an Ericsson GSM System
Figure 1-1. Objectives
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GENERAL INFORMATION
Ericsson has been involved in GSM since its inception and took an
active part in the GSM specification process. Ericsson is the largest
supplier of GSM equipment in the world with a market share of
approximately 40%. Over 477 GSM networks worldwide are
supplied by Ericsson. Ericsson, in partnership with Sony
Corporation, is one of the leading suppliers of GSM mobile phones
and has sold around 390 million mobile phones to date.
Ericsson provides two systems for GSM networks:
•
•
Cellular Matra Ericsson (CME) 20: for GSM 900 and GSM
1800 networks
Cellular Mobile System (CMS) 40: for GSM 1900 networks
ERICSSON'S GSM SYSTEM ARCHITECTURE
Like the GSM system model itself, Ericsson’s GSM systems are
split into two primary systems: the Switching System (SS) and the
Base Station System (BSS). However, depending on the
requirements of a network operator, Ericsson’s GSM systems can
incorporate other functions and nodes, such as Mobile Intelligent
Network (MIN) nodes, Flexible positioning nodes and post
processing systems.
EMM (BGW)
HLR
EMA (SOG)
MMS
MPS
FNR
EIR
ILR
SDP
SCP
Auc
BSC/TRC
PCU
MSC
RBS
STM/TDM
Based
Transit Network
SGSN
GMSC
GGSN
PSTN
ISDN
PLMN
Internet
Intranet
IP Backbone
OSS
Figure 1-2. Ericsson GSM network system mode
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GSM BSC Operation
NETWORK NODES
MOBILE SERVICES SWITCHING CENTER/VISITOR LOCATION
REGISTER (MSC/VLR)
The MSCs in all Ericsson GSM networks are AXE exchanges. In
all Ericsson GSM networks, the VLR is integrated into the MSC
node. This means that signaling between the VLR and the MSC is
done internally within the MSC/VLR network node and does not
have to be carried over the rest of the network. This has the benefit
of reducing the overall signaling load on the network.
International Mobile Subscriber Identity (IMSI)
The IMSI is a unique identity allocated to each subscriber. It is
used for identification over the radio path and in the PLMN
network. All network-related subscriber information is connected
to the IMSI. The IMSI is stored in the SIM, HLR and VLR.
The IMSI consists of three parts:
IMSI= MCC + MNC + MSIN
MCC Mobile Country Code
MNC
Mobile Network Code
MSIN
Mobile Station Identification Number
Table 1-1. IMSI
According to the GSM specifications, IMSI has a maximum length
of 15 digits.
Maximum 16 digits
2
3 digits
1-3 digits
MCC
MNC
MSIN
National MSI
IMSI
IMSI=MCC+MNC+MSIN
Figure 1-3. IMSI
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1 System Description
Temporary Mobile Subscriber Identity (TMSI)
The TMSI is used to protect the subscriber's privacy on the air
interface. The TMSI should not consist of more than four octets.
Location Area Identity (LAI)
The LAI is used for paging and tells the MSC which Location
Area (LA) the MS is located in. It is also used for location
updating of mobile subscribers.
The LAI comprises the following:
LAI= MCC + MNC + LAC
MCC Mobile Country Code, the same as the IMSI MCC
MNC
Mobile Network Code, the same as the IMSI MNC
LAC
Location Area Code - max length of the LAC is 16 bits,
enabling max 65,536 LAI to be defined in one PLMN
Table 1-2. LAI
3 digits
MCC
2
1-3
digits
MAX 16 bits
MNC
LAC
LAI
LAI=MCC+MNC+LAC
Figure 1-4. LAI
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Cell Global Identity (CGI)
The CGI is used for cell identification within a location area. The
Cell Identity (CI) is added to the LAI. The CI is max 16 bits.
The CGI consists of:
CGI= MCC + MNC + LAC + CI
3 digits
MCC
1-3 digits
MAX 16 bits
MNC
LAC
MAX 16 bits
CI
Location Area Identity
Cell Global Identity
CGI=MCC+MNC+LAC+CI
Figure 1-5. CGI
GATEWAY MOBILE SERVICES SWITCHING CENTER (GMSC)
The GMSC is also implemented as an AXE exchange. In effect, it
is an MSC with some additional software.
Mobile Station ISDN Number (MSISDN)
The MSISDN is a number, which uniquely identifies a mobile
telephone subscription in the PSTN numbering plan.
In GSM 900/1800, the MSISDN consists of the following:
MSISDN = CC + NDC + SN
CC
Country Code
NDC
National Destination Code
SN
Subscriber Number
Table 1-3. MSISDN
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1 System Description
NDC
CC
SN
National Mobile Number
International Mobile Station
ISDN Number
MSISDN=CC+NDC+SN
Figure 1-6. MSISDN (GSM 900/1800)
In GSM 1900, the MSISDN consists of the following:
MSISDN = CC + NPA + SN
CC
Country Code
NPA
Number Planning Area
SN
Subscriber Number
Table 1-4. MSISDN
CC
NPA
SN
National Mobile Number
International Mobile Station
ISDN Number
MSISDN=CC+NPA+SN
Figure 1-7. MSISDN (GSM 1900)
The NDC/NPA is allocated per GSM PLMN. In some countries
more than one NDC/NPA may be required for each GSM PLMN.
The length of MSISDN depends on the operator’s numbering plan.
The maximum length is 15 digits, prefixes not included.
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HOME LOCATION REGISTER (HLR)
Ericsson’s HLR is also based on AXE and can be implemented in
the same node as the MSC/VLR or as a stand-alone node.
Mobile Station Roaming Number (MSRN)
The HLR knows which MSC/VLR Service Area a subscriber is
located in. When a call is made to a mobile subscriber, the HLR
requests the current MSC/VLR to provide an MSRN as a
temporary routing number for the subscriber who gets the call.
Upon reception of the MSRN, the HLR sends it to the GMSC that
uses this number to route the call to the MSC/VLR exchange where
the subscriber who receives the call is registered.
All data exchanged between the GMSC, HLR, and MSC/VLR for
the purpose of interrogation is sent over C7/SS7.
The MSRN consists of three parts:
MSRN = CC + NDC or NPA + SN
CC
Country Code
NDC
NPA
National Destination Code
Number Planning Area
SN
Subscriber Number
Table 1-5. MSRN
Note: In this case, SN is the address of the MSC exchange.
MSISDN
IMSI
MSISDN
PSTN
MSISDN
GMSC
MSC address
HLR
MSRN
IMSI
MSRN
MSRN
MSC
IMSI
Figure 1-8.
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VLR
MSRN
MSRN
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INTERWORKING LOCATION REGISTER (ILR)
The Interworking Location Register (ILR) exists in CMS 40
networks only. An ILR makes inter-system roaming possible,
meaning that a subscriber can roam from a GSM 1900 network to
an AMPS network. The ILR consists of an AMPS HLR and a GSM
1900 VLR. In the near future the ILR will make intersystem
roaming
possible
in
both
directions
between
all
GSM/AMPS/TDMA networks.
AUTHENTICATION CENTER (AUC) AND EQUIPMENT IDENTITY
REGISTER (EIR)
The AUC and EIR are implemented either as stand-alone nodes or
as a combined AUC/EIR node. The UNIX-based AUC and the EIR
are developed by Sema Group. The AUC may alternatively reside
on an AXE, possibly integrated with a HLR.
International Mobile Equipment Identity (IMEI)
The IMEI is used for equipment identification and uniquely
identifies the equipment. The IMEI consists of the following:
IMEI = TAC + FAC + SNR + SVN
TAC
Type Approval Code - determined by a central GSM
body
FAC
Final Assembly Code - identifies the manufacturer
SNR
Serial Number - six digits uniquely identifies the
equipment
SVN
Software Version Number
Table 1-6. IMEI
6 digits
TAC
2 digits
6 digits
2 digits
FAC
SNR
SVN
IMEI
IMEISV
IMEI=TAC+FAC+SNR+SVN
Figure 1-9. IMEI
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DATA TRANSMISSION INTERFACE (DTI)
The DTI is a hardware platform which implements the GSMdefined InterWorking Function (IWF). It performs data handling
functions such as data rate conversion. DTI is implemented on an
AXE platform and is integrated in the MSC/VLR. Because it is
integrated into the AXE platform, the DTI does not need separate
operation and maintenance facilities.
TRANSCODER CONTROLLER (TRC)
The purpose of a TRC is to multiplex network traffic channels
from multiple BSCs onto one 64 kbits/s PCM channel which
reduces network transmission costs. The TRC can be combined
with the BSC or exist as a stand-alone node.
BASE STATION CONTROLLER (BSC)
The BSC in all Ericsson GSM networks is based on AXE
technology. It can be implemented as a stand-alone node or
integrated with either an MSC/VLR or a TRC.
BASE TRANSCEIVER STATION (BTS)
In Ericsson's GSM systems the BTS is included as part of a product
called RBS. The RBS also contains extra functionality which
enables the support of several GSM-defined BTSs.
Ericsson offers a wide range of RBSs for use in GSM networks:
•
•
•
•
•
•
•
•
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RBS 2101
RBS 2102
RBS 2103
RBS 2202
RBS 2301
RBS 2302
RBS 2302 MAXITE
RBS 2106
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•
•
•
•
RBS 2206
RBS 2308
RBS 2207
RBS 2401
OSS
Operation and Support System (OSS) is Ericsson’s product to
support the activities performed in an OMC and/or NMC. The
network operator monitors and controls the network through OSS
which offers cost effective support for centralized, regional and
local operations and maintenance activities. OSS is based on
Ericsson's Telecommunications Management and Operations
Support (TMOS) platform.
OSS is designed as a complete network management system which
can be used to control all the main network elements such as
MSC/VLRs, HLRs, ILRs, TRCs, BSCs, EIRs, AUCs and Mobile
Intelligent Network (MIN) nodes. OSS can also control BTSs
through the BSCs.
OSS uses a Graphical User Interface (GUI) enabling easier system
use and network management.
SERVICE CONTROL POINT (SCP)
The SCP function is the heart of the Intelligent Network (IN) Every
IN call asks the SCP for instructions on how to execute an IN
service. The SCF R9.1 has been implemented according to the
Application Modularity (AM) concept, which is a software concept
used to model applications in a flexible way.
The SCP R9.1 includes the standard CAMEL phase 2, and ATI for
CAMEL phase 3, providing the mechanisms to support operator
specific services, or services which are not covered by standardized
GSM services, also whilst roaming outside the Home PLMN
(HPLMN)
News in SCP R9.1 are system enhancements, enhanced
functionality in CAMEL phase 2, aimed for Pre-paid and other
service applications, and ATI for CAMEL phase 3. The SCP
hardware is an AXE platform.
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GSM BSC Operation
SERVICE DATA POINT (SDP)
The Ericsson Service Data Point (SDP) is database storage and
retrieval system that has been developed as an integral part of the
Network Intelligence product offerings from Ericsson. The SDP is
used in the Intelligent Network (IN) mainly for three reasons. First
it is used to safely store and handle large quantities of subscriber
data, which can significantly increase the number of subscribers
supported by the Service Control Point (SCP). Second it can be
used as a common point for a number of SCPs sharing the same
data enabling better control of data. Third it can act as an interface
to external databases making it possible to extend the IN. Due to its
open architecture and the fact that it is built from industry standard
components it is possible to use in both fixed and mobile network
applications.
PPS (PREPAID SYSTEM)
Prepaid System was the world’s first realtime charging system.
Today, it is the top-selling realtime charging solution and operators
give it top ratings for quality and flexibility and they consider the
roadmap future proof. PrePaid System /Charging System is tightly
integrated with the core network (which, by the way, doesn’t have
to have come from Ericsson). It provides a unified, Account
Centric platform for pre- and postpaid subscriptions, capable of
handling all types of voice, data and content services in real time
and with Session Supervision.
MPS
Ericsson offers a complete end-to-end solution for Location-Based
Services, LBS, comprising the Mobile Positioning System, (MPS),
content and application middleware, a range of professional
services and access to all available GSM and WCDMA mobile
terminals. The solution enables an operator a flexible and powerful
way of providing new revenue generating services such as
information services, games, friend finder and fleet/resource
management to his customers as well as fulfilling legal
requirements on locating emergency calls. Provision of locationbased services is a way for the operator to differentiate on the
market, reduce churn and increase revenues. Combining the endusers location with MMS and Java download enables very
compelling services.
The Ericsson MPS-G 6.0 is compliant with the system architecture
as it is described in the standards for LCS (3GPP TS 43.071 and TS
23.271). It also offers an Ericsson proprietary IP based interface for
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1 System Description
roaming, the Lr. interface. The solution consists of the GMPC
(Gateway Mobile Positioning Centre), the SMPC (Serving Mobile
Positioning Centre) and network features for the HLR, the
MSC/VLR and the BSC. The GMPC-part in MPS-G 6.0 can also
be shared with MPS-U, which is the corresponding MPS product
for WCDMA.
ERICSSON MULTI ACTIVATION (EMA)
The purpose of Multi Activation is to provide the operator with a
high abstraction level of the physical network and a single point of
entry for the customer care system. As default, access to Ericsson
GSM/UMTS is included, and integration with other types of
networks and vendors can be provided. Different types of Network
Elements in the mobile telephony network use different types of
protocols. Multi Activation manages conversion between different
languages, syntax and protocol stacks as well as routing. The most
important aspects from a system administrator’s point of view are
the system service performance and availability. It is therefore
important that you understand the complete system architecture
with all its connections to the Network Elements in order to get an
optimal configuration.
ERICSSON MULTI MEDIATION (EMM)
Ericsson Multi Mediation is the new name for Ericsson’s mediation
solution and is the first consolidated release with features and
functionality from both versions Billing Gateway (BGW) and.
Billing Mediation Platform (BMP).
A Billing GateWay (BGW) collects billing information or Call
Data Record (CDR) files from network elements such as MSCs and
forwards them to post-processing systems that use the files as
input. A BGW acts as a billing interface to the network elements in
an Ericsson network and its flexible interface supports adaptation
to any new types of network elements. Any internal BGW alarms
are forwarded to OSS at an OMC. A BGW is usually connected to
the customer administration and billing systems and is handled by
the administrative organization.
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MULTIMEDIA MESSAGING SERVICE (MMS)
The Multimedia Messaging Service (MMS) makes it possible for
mobile users to send multimedia messages from MMS enabled
handsets to other mobile users with MMS enabled handsets and to
email users. It also makes it possible for mobile users to receive
multimedia messages from other mobile users, email users and
from multimedia enabled applications. As such MMS builds on the
success of SMS and enhances the communication possibilities for
mobile users. As with SMS, multimedia messages are addressed
using the MSISDN, allowing re-use of existing phone book entries.
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NETWORK GPRS/EGPRS NODES
SERVING GPRS SUPPORT NODE (SGSN)
The Serving GPRS Support Node (SGSN) is a primary component
in the GSM network using. The SGSN forwards incoming and
outgoing IP packets addressed to/from a mobile station that is
attached within the SGSN service area. The SGSN provides:
•
•
Packet routing and transfer to and from the SGSN service area.
It serves all GPRS subscribers that are physically located
within the geographical SGSN service area. A GPRS subscriber
may be served by any SGSN in the network depending on its
location. The traffic is routed from the SGSN to the MS via the
BSC and the BTS.
•
Ciphering and authentication
•
Mobility management
•
Session management
•
Logical link management towards the MS
•
Connection to HLR, MSC, BSC, SMS-GMSC, SMS-IWMSC,
GGSN
Output of charging data. The SGSN collects charging
information for each MS related to the radio network usage.
Both the SGSN and the GGSN collect charging information on
usage of the GPRS network resources.
GATEWAY GPRS SUPPORT NODE (GGSN)
Like the SGSN, the Gateway GPRS Support Node (GGSN) is a
node in the GSM network using GPRS. The GGSN provides:
•
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The interface towards the external IP packet networks. The
GGSN therefore contains access functionality that interfaces
external ISP functions like routers and RADIUS servers
(Remote Access Dial-In User Service), which are used for
security purposes. From the external IP network’s point of
view, the GGSN acts as a router for the IP addresses of all
subscribers served by the GPRS network. The GGSN thus
exchanges routing information with the external network.
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GSM BSC Operation
•
•
•
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GPRS session management; communication setup towards
external network.
Functionality for associating the subscribers to the appropriate
SGSNs.
Output of charging data.
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2 Channel Concept
2 Channel Concept
Objectives:
Indicate the channels in the GSM/GPRS/EGPRS System
explaing their purpose using pictures and table available in
student material.
ƒ Explain the purpose of the logical channels used on the Air Interface
for GSM and GPRS network
ƒ Discuss the EGPRS Coding Schemes and the EGPRS interface to
RBS equipment based on network topology and interface description
and definition
ƒ Clarify the measurement procedure used by GSM terminal
equipment
ƒ Explain the purpose of System Information in GSM
Figure 2-1. Objectives
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2 Channel Concept
GSM AIR INTERFACE
CHANNEL CONCEPT
The separation between carrier frequencies is 200kHz; this
provides 124 carriers (ARFCN=Absolute Radio Frequency
Channel Number) in the GSM 800 and 900 band, 374 carriers in
the GSM 1800 band and 299 in the GSM 1900 band. Since each
carrier is shared by eight MS using FR (Full-Rate), with twice as
many for HR (Half-Rate) the total number of FR channel is:
•
•
•
124 x 8 = 992 (1984) channels in GSM 800 and GSM 900
374 x 8 = 2992 (5984) channels in GSM 1800
299 x 8 = 2392 (4784) channels in GSM 1900
FREQUENCY ALLOCATION
These frequency bands are allocated to the system as shown in
table 2-1:
up-link
down-link
GSM 800
(ARFCN-128) x 0,2 MHz +824.2 MHz
up-link frequency + 45 MHz
ARFCN=128..251
824 - 849 MHz
869 - 894 MHz
GSM 900
(ARFCN-1) x 0,2 MHz +890,2 MHz
up-link frequency + 45 MHz
ARFCN=1..124
890 - 915 MHz
935 - 960 MHz
GSM 900
G-Band
(ARFCN-975) x 0,2 MHz +880,2 MHz
up-link frequency + 45 MHz
880 - 890 MHz
925 - 935 MHz
ARFCN=0 and
975..1023
ARFCN=0 => 890.0
GSM 1800
(ARFCN-512) x 0,2 MHz +1710,2 MHz
up-link frequency + 95 MHz
ARFCN=512..885
1710 - 1785 MHz
1805 - 1880 MHz
GSM 1900
(ARFCN-512) x 0,2 MHz + 1850,2 MHz
up-link frequency + 80 MHz
ARFCN=512..810
1850 - 1910 MHz
1930 - 1990 MHz
Table 2-7.Frequency Allocation
Each of these channels, comprising one time slot on a Time
Division Multiple Access (TDMA) frame is called a physical
channel. A variety of information is transmitted between the BTS
and the MS using logical channels. Different types of logical
channels are used, depending on the type of information being
transmitted.
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Each logical channel is used for a specific purpose for example
paging, call setup or speech. The logical channels are mapped onto
the physical channels, for example speech is sent on the logical
channel Traffic Channel (TCH) and during transmission it is
allocated to a certain physical channel, say Time Slot 6 (TS6) on a
TDMA frame.
BURSTS AND FRAMES
The information contained in one time slot on the TDMA frame is
called a burst. There are five different types of bursts:
•
•
•
•
•
Normal Burst (NB): used to carry information on traffic and
control channels.
Frequency Correction Burst (FB): used for frequency
synchronization of the mobile.
Synchronization Burst (SB): used for frame synchronization
of the mobile.
Access Burst (AB): used for random access and handover
access.
Dummy Burst: used when no other type of burst is to be sent.
The relationship between bursts and frames is shown in figure 2-2.
There are two types of multi-frame:
•
•
26 -TDMA frame multi-frame used to carry TCH, SACCH, and
FACCH (A.K.A. TCH multi-frame)
51-TDMA frame multi-frame used to carry BCCH, CCCH,
SDCCH, and SACCH (A.K.A. CCH multi-frame)
A super-frame consists of 51 or 26 multi-frames and a hyper-frame
consists of 2,048 super-frames.
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2 Channel Concept
1 hyperframe = 2048 superframes = 2,715,648 TDMA frames (3 hours 28 minutes 53 seconds 760 microseconds)
0
1
2
3
4
5
6
2042 2043 2044 2045 2046 2047
1 superframe = 1326 TDMA frames ( 6.12 seconds )
(= 51 (26 - frame) multiframes or 26 (51 - frame) mulitframes )
0
1
0
2
3
47
48
1
49
24
50
25
1 (26- frame) multiframe = 26 TDMA frames (120 ms)
1 (51 - frame) multiframe = 51 TDMA frames (235 ms)
0
0
1
2
3
22
23
24
25
1
2
3
47
48
49
50
1 TDMA frame =8 timeslots (120/26 ~4.615 ms)
0
1
2
3
4
5
6
7
1 timeslot = 156.25 bit durations (15/26 ~ 0.577 ms)
( 1 bit duration 48/13 ~ 3.69 micro sec )
Normal burst (NB)
(Flag is relevant for
TCH only)
TB
3
Encrypted bits
57
Frequecy correction TB
burst (FB)
3
flag
1
Training sequence
26
flag
1
Encrypted bits
57
Fixed bits
142
Synchronization
burst (SB)
TB
3
Encrypted bits
39
Access burst (AB)
TB
8
Synchronization sequence
41
Dummy burst (DB)
TB
3
Mixed bits
58
Synchronization sequence
64
Encrypted bits
36
Training sequence
26
TB
3
Encrypted bits
39
TB
3
GP
8.25
TB
3
GP
8.25
TB
3
GP
8.25
TB
3
GP
8.25
TB: Tail bits
GP: Guard period
GP
68.25
Mixed bits
58
Figure 2-2. Bursts and Frames
LOGICAL CHANNELS
There are 12 types of logical channel in the GSM system. Two are
used for traffic, nine for control signaling and one for message
distribution.
TRAFFIC CHANNELS (TCH)
There are two types of TCHs:
•
•
LZT 123 3801 R7A
Full rate channel, - used for full rate speech at 13kbps, or data
up to 14.4kbps
Half-rate channel, - used for half rate speech at 6.5kbps, or data
up to 4.8kbps
© 2006 Ericsson
- 27 -
GSM BSC Operation
CONTROL CHANNELS
There are three different groups of control channels with each
group containing three different logical channels.
Broadcast Channels (BCH) (DL Only)
•
•
•
Frequency Correction Channel (FCCH) - used for frequency
correction of MS
Synchronization Channel (SCH) - carries information on the
TDMA frame number and the Base Station Identity Code
(BSIC) of the BTS
Broadcast Control Channel (BCCH) - Broadcasts cell
specific information to the MS
Common Control Channels (CCCH)
•
•
•
Paging Channel (PCH) - used on the DL to page the MS
Random Access Channel (RACH) - used on the UL by the
MS to request allocation of an SDCCH, either as a page
response or an access at MS call origination/registration
Access Grant Channel (AGCH) - used on the DL to allocate
an SDCCH or a TCH to an MS. An allocation to a TCH can be
done in the case of an Immediate Assignment on the TCH.
Dedicated Control Channels (DCCH)
•
•
•
- 28 -
Stand alone Dedicated Control Channel (SDCCH) - used for
system signaling during call setup or registration, UL and DL,
and the transmission of short text messages in idle mode.
Slow Associated Control Channel (SACCH) - Control
channel associated with a TCH or an SDCCH. Measurement
Reports from the MS to the BTS are sent on the UL. On the DL
the MS receives information from the BTS what transmitting
power to use and also instructions on Timing Advance (TA).
In addition, the SACCH is used for the transmission of short
text messages in busy mode.
Fast Associated Control Channel (FACCH) - Control
channel associated with a TCH. Also referred to as Fast
Associated Signaling (FAS), the FACCH works in stealing
mode. That is, 20 ms of speech is replaced by a control
message. It is used during handover, as SACCH signaling is not
fast enough. Used on UL and DL.
© Ericsson 2006
LZT 123 3801 R7A
2 Channel Concept
Cell Broadcast Channel (CBCH)
This is used only on the DL to carry Short Message Service Cell
Broadcast (SMSCB). The CBCH uses the same physical channel
as the SDCCH.
CHANNEL COMBINATION SDCCH/8
Several logical channels can share the same physical channel or
time slot. In this combination, the BCHs and CCCHs are
multiplexed onto TS0 of one of the carrier frequencies allocated to
a cell. On TS1 of the same carrier, eight SDCCHs can share the
same physical channel. An SACCH is allocated to every SDCCH.
A CBCH, using one of the SDCCH sub channels, is allocated, if
required. One full rate TCH with its associated SACCH uses one
physical channel. See Figure 2-3 and 2-4.
F S B B B B C0 C0 C0 C0 F S C1 C1 C1 C1 C2 C2 C2 C2
0
4
9
14
19
F S C3 C3 C3 C3 C4 C4 C4 C4 F S C5 C5 C5 C5 C6 C6 C6 C6
20
24
29
34
39
F S C7 C7 C7 C7 C8 C8 C8 C8 I
40
44
49
Figure 2-3. Multiplexing of BCHs and CCCHs on TS0
D0 D0 D0 D0 D1 D1 D1 D1 D2 D2 D2 D2 D3 D3 D3 D3 D4 D4 D4 D4
0
4
9
14
19
D5 D5 D5 D5 D6 D6 D6 D6 D7 D7 D7 D7 A0 A0 A0 A0 A1 A1 A1 A1
20
24
29
34
A2 A2 A2 A2 A3 A3 A3 A3 I
I
40
49
44
39
I
Figure 2-4. Multiplexing of SDCCHs and SACCHs on TS1
LZT 123 3801 R7A
© 2006 Ericsson
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GSM BSC Operation
CHANNEL COMBINATION SDCCH/4
This combination allows the Basic Physical Channel (BPC),
generally allocated for SDCCHs, to be used for TCHs. In this
combination, the SDCCHs, combined with the BCHs and CCCHs,
are assigned to TS0. Instead of 8 SDCCHs sharing the same
physical channel (SDCCH/8), this combination carries only 4
SDCCHs (SDCCH/4). (BCHTYPE=COMB ) See Figure 2-5.
This combination is advantageous in a cell where it is expected to
have less traffic generated, for example in a rural cell. The limited
signaling capacity of a combined control channel can still meet the
needs of such a cell.
A cell may support the configuration of one or more SDCCH/8
channels in addition to the combined control channel. (SDCCH/4
on TS0) as follows:
•
Up to two SDCCH/8 channels/TRX, or maximum 32 can be
supported in a cell.
A CBCH is required for the transmission of cell broadcast
messages; only one CBCH can be supported in a cell though.
F S B B B B C0 C0 C0 C0 F S C1 C1 C1 C1 C2 C2 C2 C2
0
4
9
14
19
F S D0 D0 D0 D0 D1 D1 D1 D1 F S D2 D2 D2 D2 D3 D3 D3 D3
20
24
29
34
39
F S A0 A0 A0 A0 A1 A1 A1 A1 I
40
44
49
Figure 2-5. Channel combination SDCCH/4 on TS0
For NONCB = 1B, 9C, 8D and 4A
For COMB = 1B, 3C, 4D and 2A
- 30 -
© Ericsson 2006
LZT 123 3801 R7A
2 Channel Concept
GPRS AIR INTERFACE
MULTI-FRAME STRUCTURE
A 52 frame multi-frame structure is used on the Packet Data
Channel (PDCH). The Logical Link Control (LLC) frames received
from the SGSN in a DL transfer are cut up into smaller segments
which are called radio blocks or RLC (Radio Link Control) blocks
by the Packet Control Unit (PCU). Each radio block is sent in four
consecutive bursts on a single time slot. If one MS is assigned for
example time slots 1-4, one radio block is sent in four bursts on
time slot 1, a second radio block is sent in four bursts on time slot
2, etc.
A number of Mobile Sets are assigned resources on the same time
slot(s). The header of every DL radio block contains the Temporary
Flow Identity (TFI) showing to which MS the radio block is
addressed.
In addition, the header of every DL radio block contains the UL
State Flag (USF). The USF is used to tell the MS with an UL
Temporary Block Flow (TBF) on that time slot, which MS is
allowed to send an UL radio block in the next but one group of four
bursts. In the multi-frame structure shown in Figure 2-6, the bursts
denoted by X are used in DL to send timing advance messages to
the MS. On the UL, nothing is sent in these periods. Instead the MS
uses the time in UL to perform measurements. The USF is sent
only in the DL blocks.
Packet
Header
Network Layer
User data
~ 1.6 kbytes
LLC PDU
Header
Radio Blocks
USF
Information field
RLC
RLC
BCS
Header Information
Tail
RLC
RLC
... USF Header
BCS
Information
LLC layer
≤ 1500 bytes
RLC/MAC layer
20-50 bytes
4 × 114 bits
Normal Normal Normal Normal
Burst Burst Burst Burst
B0
B1
B2
X
B3
B4
B5
Physical layer
X
B6
B7
B8
X
B9
B10
B11 X
Multiframe structure, 52 TDMA frames
Figure 2-6. Multi-frame Structure GPRS
LZT 123 3801 R7A
© 2006 Ericsson
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GSM BSC Operation
LOGICAL CHANNELS
A number of new logical channels, similar to those existing, but for
GPRS only, are standardized. The logical channels are mapped
onto the physical channels that are dedicated to packet data. These
physical channels are called packet data channels (PDCH).
CONTROL CHANNELS
Broadcast Channel
•
PBCCH Packet Broadcast Channel - The PBCCH broadcasts
parameters used by the MS to access the network for packet
transmission operation. In addition to those parameters the
PBCCH reproduces the information transmitted on the BCCH
to allow circuit switched operation, like an MS in the GPRS
attached mode only monitors the PBCCH, if existing. The
existence of the PBCCH in the cell is indicated on the BCCH.
If there is no PBCCH, the BCCH is used to broadcast
information for packet operation.
Packet Data Common Control Channels
•
•
•
•
•
PPCH Packet Paging channel - DL only, used to page MS.
PRACH Packet Random access channel - UL only, used to
request allocation of one or several PDTCHs.
PAGCH Packet Access Grant channel - DL only, used to
allocate one or several PDTCH.
PTCCH/U Packet Timing advance control channel UL Used to transmit random access bursts to allow estimation of
the timing advance for one MS in transfer state.
PTCCH/D Packet Timing advance control channel DL Used to transmit timing advance updates for several Mobile
Sets. One PTCCH/D is paired with several PTCCH/Us.
Packet Traffic Channels
•
•
- 32 -
PDTCH Packet Data Traffic channel - A PDTCH
corresponds to the resource allocated to a single MS on one
physical channel for user data transmission.
PACCH The Packet Associated Control channel - The
PACCH is bi-directional. For description purposes PACCH/U
is used for the UL and PACCH/D for the DL
© Ericsson 2006
LZT 123 3801 R7A
2 Channel Concept
CHANNEL COMBINATION MPCCH AND SPDCH
Several logical channels can share the same physical channel or
time slot. In this combination the BCHs and CCCHs are
multiplexed on TS0 of one of the carrier frequencies allocated to a
cell. This combination called MPDCH is shown in Figure 2-7.
B B B B B B B B B B B B X
0
0
0
0
1
0
1
1
1
2
2
0
2
2
12
0
B B B B B B B B B B B B X
0
3
3
3
3
4
0
4
4
4
5
5
0
5
5
25
13
B B B B B B B B B B B B X
0
6
6
6
6
7
0
7
7
7
8
8
0
8
8
38
26
B B B B B B B B B B B B X
0
9
9
9
9
10
0
10
10
10
11
11
0
11
39
11
51
Figure 2-7. GPRS TDMA Frame
In Table 2-2 below you can find the mapping for the DL and the
UL.
Down-link ↓
Up-link↑
B0 may be used as
B0-B11 may contain
PBCCH and B1-B11
PRACH, PTCCH,
may contain PBCCH,
PDTCH or PACCH.
PAGCH, PPCH,
PTCCH, PDTCH or
PACCH.
Table 2-2. UL and DL
If the PDCH is used without PCCCH the channel combination is
called SPDCCH and all blocks may be used as PDTCH or PACCH.
LZT 123 3801 R7A
© 2006 Ericsson
- 33 -
GSM BSC Operation
GPRS CODING SCHEMES
GPRS employs four different channel coding schemes, CS1
through CS4 to encode data over the air interface. These coding
schemes achieve different error correcting capabilities and hence
different data rates when transmitting packet switched information
over the air interface in order to compensate for different radio
environments.
CS1, the most robust coding scheme is always used for signaling
while CS2//CS4 as well as CS1 can be used for data transfer.
CS2 utilizes error protection that is more robust than that required
for speech protection. A data-link between the GPRS terminal and
the network is established under radio-link conditions that would
induce unacceptable speech quality in GSM.
Coding schemes CS3 and CS4 are also standardized within the
GPRS specifications. They are supported only in the downlink. All
GPRS terminals will support CS3/CS4 in addition to the lower
coding schemes CS1 and CS2. Total available bandwidth in a cell
is increased when support for CS3/CS4 is included by allowing
more users to share the GPRS resources over time with maintained
quality.
All GPRS coding schemes as defined in the GPRS standard are
shown in Table 2-3:
Coding
scheme
CS1
CS2
CS3
CS4
Modulation Maximum throughput per
timeslot (RLC/MAC user data)
GMSK
9.05 kbps
GMSK
13.4 kbps
GMSK
15.6 kbps
GMSK
21.4 kbps
Table 2-3. GPRS Coding Schemes
The choice of coding scheme depends on the condition of the
channel provided by the Radio Access Network (RAN). If the
channel is very noisy, the network may use CS1 to ensure higher
reliability; in this case the data transfer rate is only 9.05 kbps per
GSM time slot used. If the channel provides good conditions, the
network could use CS3 or CS4 to obtain optimum speed, and
would then have up to 21.4 kbps per GSM time slot. CS1 through
CS4 are available for downlink data transfer, whereas on the uplink
only CS1 and CS2 are used.
- 34 -
© Ericsson 2006
LZT 123 3801 R7A
2 Channel Concept
To optimize data throughput on packet transfers, GPRS Link
Adaptation dynamically selects at all times the most appropriate
coding scheme of the four standardized coding schemes.
Support for CS3/CS4 and Link Adaptation can be activated on a
per cell basis. The number of Basic Physical Channels per Channel
group supporting CS3/CS4 is specified. Link Adaptation is
activated when required. The command structure is shown below.
RLBDC:CELL=cell[,CHGR=chgr],NUMREQBPC=numreqbpc,
[NUMREQEGPRSBPC=numreqegprsbpc,
[NUMREQCS3CS4BPC= numreqcs3cs4bpc] …;
No. of BPCs supporting CS3/CS4 set by NUMREQCS3CS4BPC
RLGSC:CELL=cell,[FPDCH=fpdch],[LA=la]… ;
Link Adaptation turned on with LA=ON
ENHANCED GPRS (EGPRS)
EGPRS utilizes modulation and protocol enhancements to GPRS in
order to take advantage of EDGE (Enhanced Data Rates for
GSM/Global Evolution) enhancements to RBS hardware to further
increase packet data transfer rates over the air interface.
EGPRS uses a number of Modulation Coding Schemes (MCS),
which are a combination of GMSK and 8PSK techniques
illustrated in Figure 2-8, for modulation on the radio interface.
Different MCSs are allocated to allow a more precise adaptation to
the actual radio environment. Reservation of the maximum eight
timeslots per user combined with the higher coding scheme allows
data rates in excess of 384 kbps (ITU definition of 3G).
S P S K M o d u la tion
S P S K M o d u la tion
(0 ,1 ,0)
Q
Q
(0 ,0 ,0)
(0 ,1 ,1)
“1”
I
I
(0 ,0 ,1)
“0”
(1 ,1 ,1)
(1 ,0 ,1)
(1 ,1 ,0)
(1 ,0 ,0)
“1 b its per s ym bol”
“3 bits p er s ym b ol”
Figure 2-8. Principle of EDGE Modulation
LZT 123 3801 R7A
© 2006 Ericsson
- 35 -
GSM BSC Operation
The EGPRS coding schemes are defined in three families A, B and
C (see Table 2.4). Overhead packets can be re-transmitted over the
air interface providing they use a coding scheme belonging to the
same family. This means that re-segmentation can be done from
e.g. MCS9 to MCS6 or from MCS6 to MCS3. The possibility of
re-transmitting a packet that was not received correctly with a more
robust MCS results in a dramatically increased overall throughput.
Scheme
MCS9
MCS8
MCS7
MCS6
MCS5
MCS4
MCS3
MCS2
MCS1
Modulation
8PSK
8PSK
8PSK
8PSK
8PSK
GMSK
GMSK
GMSK
GMSK
Throughput / TS
59.2 kbps
54.4 kbps
44.8 kbps
29.6 kbps
22.4 kbps
17.6 kbps
14.8 kbps
11.2 kbps
8.8 kbps
Family
A
A
B
A
B
C
A
B
C
Table 2-4 MCS Coding Schemes
Link Quality Control (LQC) mechanism attempts to achieve the
highest possible data throughput for a given radio environment by
using the most appropriate MCS. It does this by combining Link
Adaptation (LA) and Incremental Redundancy (IR). LA uses the
radio link quality measured by the MS on the downlink data
transfer to choose the most appropriate MCS to use in the next
sequence of packets to be transmitted. IR monitors the information
received at the MS from the first transmission where very little
coding is used. If this information is overhead, then more coding is
used i.e. the MCS will be changed for example from MCS9 to
MCS3. This extra coding is then soft combined with the previously
received coding information to increase the possibility of
successful decoding. This soft combining within the MS continues
until the information can be successfully decoded. If the MS
memory becomes insufficient whilst working in IR mode, the PCU
will switch to LA mode.
As packets can be re-transmitted using another MCS (see above),
LQC achieves extremely high throughputs. This combination of
mechanisms significantly improves the performance compared to a
pure LA solution. On the downlink, full LQC support is provided
(Incremental Redundancy and Link Adaptation). On the UL and
DL all MCSs are supported and Link Adaptation is used.
- 36 -
© Ericsson 2006
LZT 123 3801 R7A
2 Channel Concept
Utilization of Coding Schemes CS3 and CS4 in GPRS and EGPRS
supports data rates of up to 59.2 kbps per TS on the radio interface.
To support these on the Abis interface, it must be possible to
configure channels with bandwidth allocation of up to 64 kbps. At
definition of the Transceiver Group (TG) the number of RBLT
devices reserved for 64 kbps is set as illustrated in Fig 2-9.
BSC
TS0
PCM
Sync
TS1
TRX Sig
(OML,RSL)
64k
TS2
TCH 0
64k
TS3
TCH 1
64k
TS5
TS6
TCH 3
64k
TCH 4
TCH 5
TCH 6
TCH 7
64k
TS4
TCH 2
64k
RXAPI:MO = mo,DEV=dev,DCP=dcp,RES64k;sets Abis rate
Figure 2-9. 16 & 64 kbps Time slots on the Abis Interface
See also the command structure for command RXAPI and Chapter
3 – Connection of TG, Model G12 for details of this connection in
the RBS2000 and on the Abis interface.
LZT 123 3801 R7A
© 2006 Ericsson
- 37 -
GSM BSC Operation
HIGH SPEED CIRCUIT SWITCHED DATA
As the data rate increases with the existing types of data
transmission, single time slot and multi time slot, the increase in
throughput is available for all types of data services. On single time
slot transmissions the rate will increase from 9.6 kbit/s to 14.4
kbit/s for transparent data (and to 13 kbit/s for non-transparent
data). In circuit switched multi-slot services, the maximum rate
which uses 4 TSs will thereby increase from 38.4 to 57.6 kbit/s on
the radio interface - See Figure 2-10. To achieve the higher rates a
new channel coding, with less protection, is applied to the radio
interface. The 14.4 kbps service is requested in a similar way to a
9.6kbps connection, that is both network and mobile may request
the service. The mobile must be capable of handling 14.4kbps and
indicate this with the appropriate Mobile Station class mark to the
network.
14.4kbps channel coding is used to increase transmission speed in
circuit switched data applications utilizing one or more timeslots
and is also designed to reduce the transmission time for file
transfer. This feature will increase the data rate by 50% for
transparent data in circuit switched data calls in a network, when
compared to the standard 9.6 kbps rate. The increase is slightly less
for non-transparent data.
0
1
2
3
4
5
6
7
Figure 2-10. HSCSD
The high increase is achieved by a higher data rate per timeslot in
all circuit switched data applications, both for single and multitimeslot configurations. An HSCSD configuration consists of one
main channel and up to three secondary channels. Only the main
channel carries a Fast Associated Control Channel (FACCH). The
Timing Advance control is handled in main channel.
- 38 -
© Ericsson 2006
LZT 123 3801 R7A
2 Channel Concept
Capacity savings due to multi-time slot applications use less time
slots for the same throughput. (An application running at 28.8
kbit/s only needs two timeslots at 14.4 kbit/s instead of up to three
at 9.6 kbit/s.)
LZT 123 3801 R7A
© 2006 Ericsson
- 39 -
GSM BSC Operation
CALL SETUP MOBILE TERMINATED CALL
This call case is an example of how logical channels are used in a
GSM call. Below is the description of the call set-up procedure for
a call from a PSTN subscriber to a mobile subscriber. The steps
involved in a call setup are as follows:
GSM/PLMN PSTN
3.
5.
1.
GMSC
2.
HLR
5.
Local
exchange
1.
6.
4.
MSC/VLR
7.
11.
BSC/TRC
8.
11.
8.
10.
9.
8.
8.
9.
10.
11.
Figure 2-11. Call to MS from PSTN
- 40 -
1.
The PSTN subscriber keys in the MS’s telephone number
(MSISDN). The MSISDN is analyzed in the PSTN, which
identifies that this is a call to a mobile network subscriber. A
connection is established to the MS’s home GMSC.
2.
The GMSC analyzes the MSISDN to find out which HLR the
MS is registered in, and queries the HLR for information about
how to route the call to the serving MSC/VLR.
3.
The HLR translates MSISDN into IMSI, and determines which
MSC/VLR is currently serving the MS. The HLR also checks
if the service, “Call forwarding to C–number” is activated. If
so, the call is rerouted by the GMSC to that number.
4.
The HLR requests an MSRN from the serving MSC/VLR.
5.
The MSC/VLR returns an MSRN via HLR to the GMSC.
6.
The GMSC analyses the MSRN and routes the call to the
MSC/VLR.
© Ericsson 2006
LZT 123 3801 R7A
2 Channel Concept
7.
The MSC/VLR knows which LA the MS is located in. A
paging message is sent to the BSCs controlling the LA.
8.
The BSCs distribute the paging message to the RBSs in the
desired LA. The RBSs transmit the message over the air
interface using PCH. To page the MS, the network uses an
IMSI or TMSI valid only in the current MSC/VLR service
area.
9.
When the MS detects the paging message, it sends a request on
RACH for a SDCCH.
10. The BSC provides a SDCCH, using AGCH.
11. SDCCH is used for the call set-up procedures. Over SDCCH
all signaling preceding a call takes place. This includes:
•
•
•
•
Marking the MS as “active” in the VLR
The authentication procedure
Start ciphering
Equipment identification
12. The MSC/VLR instructs the BSC/TRC to allocate an idle
TCH. The RBS and MS are told to tune to the TCH. The
mobile phone rings. If the subscriber answers, the connection
is established.
LZT 123 3801 R7A
© 2006 Ericsson
- 41 -
GSM BSC Operation
MEASUREMENT PROCEDURE
MEASUREMENTS IN IDLE MODE
When an MS is in idle mode (powered on and not on a call), it
measures carrier frequencies to see if it should remain in the
serving cell or select a new cell as the serving cell. The MS scans
all radio frequency channels in the system, and calculates average
power levels for each.
The MS tunes to the strongest carrier and determines if it is a
BCCH carrier. If so, the MS reads the BCCH data to find out if the
cell can be locked to (chosen PLMN, barred cell, etc.). Otherwise,
the MS tunes to the next strongest cell, etc.
Once the MS has camped on the BCCH in a cell, it receives a bitmap describing which BCCH frequencies neighboring cells use.
Up to 32 BCCH frequencies can be set to define neighboring cells.
The path loss criterion parameter C1 used for cell selection/reselection is defined by:
C1 = A - B if B > 0 or
C1 = A - 0 if B < 0 where
A = RXLEV-ACCMIN
B = CCHPWR - P
RXLEV
received signal strength level in the MS from
BTS (down-link)
ACCMIN
minimum received signal strength level in
the MS required for system access (downlink)
CCHPWR
maximum signal strength (MS TXPWR)
level the MS may use when accessing the
system (up-link)
P
maximum RF output power of the MS (uplink)
All values are expressed in dBm.
The C1 parameter is used to make sure that the MS camps on the
cell with the highest probability of successful communication on
the UL and DL. See Figure 2-12.
- 42 -
© Ericsson 2006
LZT 123 3801 R7A
2 Channel Concept
Note: Phase 2 mobiles use the C2 criteria; refer to chapter 4 “Radio
Network”, heading “System Information on BCCH Data”.
Scan RF channel and measure
Signal strength for 3.5 seconds
Tune to the RF channel with the
Highest received average signal
Strength.
Determine if it is a BCCH carrier
By searching for frequency
Correction bursts.
No
Tune to the RF channel with the
Highest signal strength not
already tried.
Is it a BCCH carrier?
Yes
The MS shall attempt to synchronize to this
Carrier and read BCCH info.
No
Does the carrier belong to the
Wanted PLMN
Yes
Yes
Is the cell barred for
Access
No
No
Is c1 > 0
Yes
Camp on the cell
Figure 2-12. Cell Selection
The MS attempts to change cells if one of the following conditions
should occur:
•
•
Cell becomes barred
•
Too many errors on the DL
•
MS has tried to access a number of times without success
•
C1 < 0 for five seconds
C1 is better in another cell for five seconds
MEASUREMENTS IN ACTIVE MODE
During a call, the MS continuously reports to the system via
SACCH how strong the received signal strength from the
neighboring cells that it has been told to measure is. The format of
these measurements is a Measurement Report, which is transmitted
every 480ms (refer to the section in this chapter on Measurement
Reports). These measurements are used by the BSC to make
decisions about target cells if handover is required.
LZT 123 3801 R7A
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GSM BSC Operation
Measurements of neighboring cells during a call take place in
between the times when the MS is transmitting and receiving
information. Hence the procedure of the MS is receive-transmitmeasure-receive-transmit-measure.
The signal strength of the serving cell is monitored during
reception by the time slot allocated to the MS. On an SACCH, the
MS is informed which BCCH carriers in neighboring cells to
measure. The signal strength of these is measured one by one. The
mean values of the measurements for a maximum of 32 carrier
frequencies are then derived and reported to the BSC.
Each measurement is matched to its corresponding BTS identity.
The BTS identity is contained in the BSIC sent on SCH. Thus,
during the idle frame on the TCH, BSICs for neighboring BTSs are
read. The BSICs of the six neighboring cells with the highest mean
signal strength are then reported to BSC in the Measurement report
via SACCH.
Figure 2-13. MS Measurement Principle
The procedure used by the MS for measurements on neighboring
cells is according to Steps 1-4 shown in Figure 2-13.
1. MS receives and measures SS on serving cell, TS2.
2. MS transmits.
3. MS measures SS for at least one of the surrounding cells.
4. MS reads BSIC on SCH (TS0) for one of the surrounding cells.
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© Ericsson 2006
LZT 123 3801 R7A
2 Channel Concept
SLIDING MULTI-FRAMES
Since the MS might not be synchronized with the neighboring cell
whose identity it is trying to determine, the MS might not have any
information regarding when TS0 on the adjacent BCCH carrier will
occur. Therefore measurements are taken over a time period of at
least eight time slots to be sure that TS0 will occur. This is done
during the IDLE frame (Figure 2-14).
However, it is not sufficient to be able to read only TS0. Remember
that the multi-frame comprising the SCH is organized so that only
every tenth transmitted TS0 supports an SCH. The chances are high
that the mobile will listen to, for example, a BCCH or CCCH
instead of an SCH. To solve this, the multi-frame carrying TCHs is
slid compared to the multi-frame carrying control channels as
illustrated in Figure 2-14.
5 1 fra m e s = 2 3 5 .4 m s
F S
B
C
FS
C
C
FS
C
F S
C
C
C
A
TCH
A
A
A
A
A
A
A
A
A
A
A
A
A
A
A
A
A
A
A
A
A
A
A
1326 frames = 6.12 sec
A
A
C
A
A
A
C
A
A
A
FS
A
A
A
A
A
A
A
A
A
A
A
A
A
A
A
A
A
A
A
Figure 2-14. Sliding Multi-frames
LZT 123 3801 R7A
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GSM BSC Operation
MEASUREMENT REPORT
The MS measures the signal strength of the Broadcast carrier in
neighboring cells. The MS also reads the SCH of each neighboring
cell and obtains the BSIC of the neighboring cells on the SCH.
When the MS’s power is turned on, or when the MS enters a new
cell, it is provided with a list of neighboring cells to measure. This
list is stored in both the MS and the BSC. There is a list in the MS
with 124, 374 or 299 multiple positions, which are equal to the
number of carrier frequencies depending on the system (GSM
900/1800/1900). Each neighboring cell the MS is told to measure is
noted by setting a flag on the list.
The MS sends complete measurement reports to the BSC, on
SACCH every 480ms. One measurement report contains the signal
strength and quality measured on the DL for the serving cell and
the measured signal strength for a maximum of six neighboring
cells. These measurement reports are received by the BTS, where
the BTS adds the signal strength and quality of the connection on
the UL. Then the reports are received by the BSC where they are
used as an input to the locating algorithm.
After processing the reports, the locating algorithm output is a list
of possible handover candidates called the PO-cell list. Each
neighboring cell is ranked using the reported signal strength. If the
serving cell is at the top of the list (that is, has the strongest signal
strength) no handover will take place.
INFORMATION ELEMENTS
The information elements in the measurement report are described
in these sections.
BA-USED
If the list of neighboring cells is changed by the operator, this
parameter (set = 1 or 0) toggles. It tells the locating algorithm in
the BSC which neighboring cells description the MS has used, that
is, the updated one or the old one.
DTX-USED
This bit indicates if the MS used Discontinuous Transmission
(DTX) on the UL.
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© Ericsson 2006
LZT 123 3801 R7A
2 Channel Concept
RXLEV-FULL-SERVING-CELL / RXLEV-SUB-SERVING-CELL
These elements contain the average received signal strength of the
serving cell, measured on all time slots and on a subset of time
slots. The full set of TCH and SACCH frames is either 100 frames
for full rate TCH or 50 frames for half rate. The subset consists of 4
SACCH frames and 8 SID frames and is significant when DTX is
used on the DL. The signal strength is mapped to an RXLEV value
between 0 and 63:
RXLEV 0 = less than -110dBm
RXLEV 1 = -110dBm to -109dBm
RXLEV 63 = greater than -48dBm
RXQUAL-FULL-SERVING-CELL / RXQUAL-SUB-SERVING-CELL
These elements contain the average received signal quality on the
serving cell, measured on all time slots and on a subset of time
slots. The received signal quality is mapped to a corresponding Bit
Error Rate (BER) value before decoding, as follows:
RXQUAL 0
BER less than 0.2%
RXQUAL 1
BER = 0.2% to 0.4%
.
.
.
RXQUAL 7
BER greater than 12.8%
Note: The subset is used for both RXLEV and RXQUAL, if DTX
is employed. Otherwise, the full set is used.
MEAS-VALID
The MS must send continuous measurement reports, but if for
some reason it does not have the measurements, it can indicate this
to the network with this bit.
NO-NCELL-M
These three bits indicate the number of neighboring cell
measurements.
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GSM BSC Operation
RXLEV-NCELL
These elements contain the measured signal strength of the nth
neighboring cell (n = 1 to 6). This field is coded in the same way as
the field for the serving cell.
BCCH-FREQ-NCELL
This field is coded as the absolute binary representation of the
position of the nth neighboring cell in the BCCH allocation list
(BA list). The BCCH allocation list is the list of the RF channel
numbers for which the bit is set to 1 in the neighboring cell
description parameter. With 5 bits, one of 32 (range 0-31)
neighboring cells can be pinpointed.
BSIC-NCELL
This element indicates the BSIC of the nth neighboring cell. BSIC
consists of 6 bits. Figure 2-15 illustrates the logical organization of
the Measurement Report.
8
7
6
SKIP INDICATOR
0
0
0
BA
USED
5
4
3
2
1
PROTOCOL DISCRIMINATOR
1
0
1
0
1
Message Type
Octet 0
Octet 1
DTX
RXLEV-FULL Serving Cell
USED
MEAS
RXLEV-SUB Serving Cell
VALID
RXQUAL-FULLRXQUAL-SUBNC
Serving Cell
Serving Cell
Octet 2
NC
RXLEV-NCELL 1
BSIC-NCELL 1
BCCH-Freq NCELL 1
BSIC-NCELL 1
Octet 5
Spare
Spare
Number 2
Octet 3
Octet 4
Octet 6
Octet 7
Octet 8
Octet 9
Octet 10
Number 3
Octet 11
Number 4
Octet 12
RX 5
RXLEV-NCELL 5
BCCH Freq Ncell 5
BSIC-NCELL 5
BF 5
RX 6
RXLEV-NCELL 6
BCCH Fr 6
BF 6
BSIC-NCELL 6
Octet 13
Octet 14
Octet 15
Octet 16
Octet 17
Figure 2-15. Layout of Measurement Report
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© Ericsson 2006
LZT 123 3801 R7A
2 Channel Concept
SYSTEM INFORMATION
The purpose of this function is to supply the BTS with system
information messages. System information messages are
continuously sent by the BTS to all MSs in a cell on a BCCH (idle
MS) or an SACCH (busy MS). The parameters sent in these
messages are either controlled internally in the BSC, or they are set
externally via commands by the operator. In the latter case, they are
defined as permanent exchange data. Each cell has its own set of
parameters.
This function assembles and distributes complete System
Information messages. In a GSM system, eight different System
Information message types are used, as follows:
•
•
•
•
•
•
•
•
Type 1: BCCH
Type 2: BCCH
Type 3: BCCH
Type 4: BCCH
Type 5: SACCH
Type 6: SACCH
Type 7: BCCH
Type 8: BCCH
Hopping info
BA list info
LAI, Cell info
CBCH
Measurements TA MSTXPWR
Cell options
opt. Cell reselect parameters
opt. Cell reselect parameters
Distribution is also performed when a parameter is changed while a
cell is in an ACTIVE or changed from HALTED to ACTIVE State.
SYSTEM INFORMATION TYPE 1
When frequency hopping is used in a cell, the MS needs to know
which frequency band and which frequencies within the band to
use in the hopping algorithm. If the global system type is set to
MIXED, meaning that more than one system type is allowed, the
cell system type must be stated at each cell definition. Information
is also provided about how the MS should access the system. This
information is given in the RACH control parameters.
Cell Channel Description
CANO
Cell Allocation Number. Shows the band
number (0-2). Band 0 is used for GSM.
CA ARFCN
This is the Absolute Radio Frequency channel
number used in a cell.
Table 2-5. Cell Channel Description
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GSM BSC Operation
RACH Control Parameters
ACC
This is the Access Control Class and it defines
which access classes are barred.
CB
Cell barred for access
RE
Call re-establishment allowed
MAXRET
This is the maximum number of CHANNEL
REQUEST message re-transmissions allowed
when an MS attempts to access the system.
TX
This is the random number of TDMA frames
to spread access re-transmissions when an MS
attempts to re-access the system.
Table 2-6 RACH PARAMETERS
SYSTEM INFORMATION TYPE 2
The System Information Type 2 message consists of the Double
BA list, which defines the BCCH frequencies, used in the
neighboring cells. The MS needs this information to monitor the
system information in neighboring cells, as well as when
measuring the signal strength of the neighboring cells. The Double
BA list provides the MS with the different frequencies on which to
measure, depending on whether the MS is in idle or active mode. In
active mode, the MS should measure on a reduced number of
frequencies in order to improve the accuracy of the measurements.
In idle mode, the MS should measure on a larger number of
frequencies, so that the time required for the MS to access the
network after power on is reduced. The MS is also informed which
PLMNs it may use.
In addition to System Information Type 2, it is possible to have
System Information Type 2 Bis and System Information Type 2
Ter, depending on the size of the BA list. If it is not possible to fit
the BA list into the first message, then the second (Type 2 Bis) will
be used. There may be a large number of frequencies in the lists if
Multiband Operation is in use, then the frequencies from other
bands will be included in the Type 2 Ter message.
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© Ericsson 2006
LZT 123 3801 R7A
2 Channel Concept
Neighboring Cells Description
BAIND
The BCCH allocation sequence number
indicates if the description is sent on the
BCCH or the SACCH.
BANO
The BCCH Allocation Number. Band 0 is used
for GSM.
MBCCHNO
Absolute RF channels (ARFCNs) on which the
MSs should perform and report signal strength
measurements.
Table 2-7. Neighboring Cells Description
PLMN Permitted
NCCPERM
This parameter states the permitted PLMN
color codes and it tells the MS which Network
Color Codes (NCC) on the BCCH carriers it
is allowed to monitor when in this cell.
Table 2-8 PLMN Permitted
RACH Control Parameters
Parameters as described in System Information Type 1.
SYSTEM INFORMATION TYPE 3
The System Information Type 3 contains information on the
identity of the current LA and cell identity. A change means that the
MS must update the network. In order to calculate its paging group,
the MS needs some of the parameters contained in the Control
Channel Description. This description also informs the MS about
periodic registration.
In addition, System Information Type 3 contains information for
the MS in the Cell Options parameters, to achieve good cell
performance. When the MS is in idle mode it determines which
cells to lock onto. The information needed by the MS for cell
selection is also broadcast in the Type 3 information.
LZT 123 3801 R7A
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GSM BSC Operation
Cell Identity
CI
Cell Identity within a LA
Table 2-9 Cell Identity
Location Area Identity (LAI)
MCC
Mobile Country Code
MNC
Mobile Network Code
LAC
Location Area Code
Table 2-10 LAI
Control Channel Description
ATT
Attach/Detach allowed
CCCHCONF This is the number of basic physical channels used for
the CCCH. (1-4 BPCs in the case of non-combined
common control channel, 1 BPC in the case of
combined common control channel with SDCCH.)
AGBLK
This is the number of CCH blocks reserved for the
Access Grant CHannel (AGCH). In GSM 900/1800/
1900, the AGCH always has priority over PCH.
MFRMS
Multi-frames period for transmission of
PAGING REQUEST messages to the same
paging group.
T3212
Time-out value for periodic updating.
Table 2-11 Control Channel Description
Cell Options
DTX
Discontinuous transmission indicator.
PWRC
Power control indicator.
RLINKT
Radio link time-out is the time before an MS
disconnects due to failure in decoding SACCH
messages.
Table 2-12 Cell Options
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© Ericsson 2006
LZT 123 3801 R7A
2 Channel Concept
Cell Selection Parameters
ACCMIN
This is the permitted minimum received signal
strength for the MS to access the system.
CCHPWR
Maximum transmission power an MS may use
when accessing the system.
CRH
This is the Cell Reselect Hysteresis. If the
neighboring cell belongs to a new LA, the
measured signal strength of the serving cell is
artificially increased to make handover to the
neighboring cell more difficult.
Table 2-13 Cell Selection Parameters
RACH Control Parameters
See RACH parameters described in System Information Type 1.
SYSTEM INFORMATION TYPE 4
The operator can broadcast text messages to all idle MSs in a cell.
Each MS knows that if the cell broadcast function is used, it must
listen to this channel at certain time intervals. However, the MS needs
to know what frequency carries the CBCH. This frequency is provided
in System Information Type 4. The LAI, the Cell Selection
parameters, and the RACH control parameters are also included.
CBCH Description (Optional)
CHN
This is the channel number for CBCH. It is
controlled internally in BSC.
TSC
Training Sequence Code. Base Station Color
code (BCC) part of BSIC is used.
CBCHNO
Absolute RF channel number for CBCH.
MAC
Mobile Allocation in the cell describes the
frequencies to be used in the hopping
sequence, if frequency hopping is used.
Table 2-14 CBCH
LZT 123 3801 R7A
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GSM BSC Operation
Location Area Identity
Refer to the Location Area Identity parameters described in System
Information Type 3.
Cell Selection Parameters
Refer to the Call Selection parameters described in System
Information Type 3.
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© Ericsson 2006
LZT 123 3801 R7A
2 Channel Concept
RACH PARAMETERS
See RACH parameters described in System Information Type 1.
SYSTEM INFORMATION TYPE 5
When the MS is in ACTIVE mode, an SACCH is activated. The
MS sends measurement reports on the UL and the network sends
output power and TA for the MS on the DL. In addition, the MS
receives information about the BCCH carrier in each neighboring
cell on the SACCH. The frequencies in the neighboring cells
description may differ from those sent in System Information Type
2.
In addition to System Information Type 5, it is possible to have
System Information Type 5 Bis and System Information Type 5
Ter, depending on the size of the BA list. If it is not possible to fit
the BA list into the first message, the second (Type 5 Bis) will be
used. There may be a large number of frequencies in the lists if
Multiband Operation is in use. The frequencies from other bands
will then be included in the Type 5 Ter message.
System Information Type 5 Bis/Ter is optional.
Neighbor Cells Description
CANO
Cell Allocation Number. Band 0 for GSM.
ARFCN
This indicates which neighboring BCCH
frequencies the SS should be measured on.
Table 2-15 Neighbor cell description
SYSTEM INFORMATION TYPE 6
When in active mode, the MS needs to know if the LAI changes. If
so, it must perform location updating when the call is released. The
MS may change between cells (within the location area) where
RLINKT or DTX conditions differ. Therefore Cell Options
parameters must be sent to the MS. The PLMN permitted is also
included in Type 6 information.
Location Area Identity
Refer to the Location Area Identity parameters described in System
Information Type 3.
LZT 123 3801 R7A
© 2006 Ericsson
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GSM BSC Operation
Cell Identity
Refer to the Cell Identity parameters described in System
Information Type 3.
Cell Options
Refer to the Cell Options parameters described in System
Information Type 3.
PLMN Permitted
Refer to the PLMN Permitted parameters described in System
Information Type 2.
SYSTEM INFORMATION TYPE 7/TYPE 8 (OPTIONAL)
System Information Types 7 and 8 contain Cell Reselect
parameters. Their function is to supplement System Information
Type 4.
DISTRIBUTION OF SYSTEM INFORMATION MESSAGES
A cell in operation is in ACTIVE State. A cell not in operation is in
HALTED State. The System Information messages are distributed
to the BTS when the cell state is either changed from HALTED to
ACTIVE or when the parameters sent in System Information
messages are changed while the cell is ACTIVE.
If, as an example, parameter MBCCHNO is changed, System
Information messages Types 2 and 5 are distributed. BTS
equipment supporting the BCCH or SACCHs taken into service in
a cell that is ACTIVE is updated within System Information
messages. To prevent major disturbances on the system caused by
lost messages or inaccurate messages arriving at the BTS, all
System Information messages are regularly distributed to the BTS
for all cells where BCCH is transmitted.
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© Ericsson 2006
LZT 123 3801 R7A
2 Channel Concept
GSM – WCDMA CELL RESELECTION AND HANDOVER
Introduction of WCDMA mobile networks by operators utilizing
their own GSM networks or those of other operators as last resort
coverage in areas where WCDMA network capacity is not
available requires GSM to WCDMA cell reselection and handover.
An already established GSM area can be used, so that end-users
with Multi-RAT MSs (Multi-Radio Access Technology) will
experience good coverage where there is no WCDMA RAN
available by using the WCDMA to GSM cell reselection and
handover functionality.
HANDOVER TO GSM
The basis for WCDMA to GSM handover decisions is implemented
in the Radio Network Controller (RNC) in the WCDMA RAN
system (see Fig 2-16). Handover can only occur with Multi Radio
Access Technology (RAT) MSs i.e. the MS must be capable of both
GSM and WCDMA working.
If the estimated quality of the currently used WCDMA RAN
frequency is below a set threshold and the estimated quality of the
target GSM cell is above a set threshold, then a handover will take
place. During handover execution the BSC is informed via the
MSC that an inter-system handover is required. The target BSC
allocates radio and Abis resources and orders the Multi-RAT MS to
access the target GSM cell via the serving RNC. The BSC does not
distinguish between incoming intra-or inter-system handovers.
LZT 123 3801 R7A
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GSM BSC Operation
G SM -W C DM A H O in B S C
MS
C
= GSM cell
SGS
N
MS
C
= W C D M A cell
BS
C
RN
C
T RC
G SM
W CDM A
R 9.0
R 9.1
•
•
•
•
•
•
•
W CDMA π
W CDMA π
W CDMA π
W CDMA π
G S M TC H , Ac tive m o d e C S , H an d o ver
G S M B C C H , Idle m o d e C S , C ell
G P Rl S , tiM M Idle P S , R A
UG d
P RtS , M M C o nn ec te d P S , C ell
d t
GSM BCCH U
π W C D M A, Id le m od e C S , C ell
ti C D M A , S ta n db y P S , R A
G S M B C C H /P B C C Hl π W
t A , R ea d y s ta te P S , C ell
G S M B C C H /P B C C H π U
W CdD M
U pd ate
G S M TC H => W C D M A , Active m od e C S , H a nd o ver
- B a se d on priority or G S M lo ad.
Figure 2-16. GSM-WCDMA Handover
HANDOVER TO WCDMA
In circuit switched active mode (speech and data), a Multi-RAT MS
is measuring neighboring WCDMA RAN cells as well as GSM
cells and reporting to the BSS through measurement reports. To be
able to perform inter-system measurements a list of WCDMA RAN
neighbors is sent to the Multi-RAT MS on the SACCH (Slow
Associated Control Channel). These lists can be the same as the list
broadcast on BCCH to Multi-RAT MSs in idle mode, but it is also
possible to set them separately in order to have different WCDMA
neighbors in idle and active mode. After changing from idle to
active mode, the last list received over BCCH is used (i.e. idle 3GBA), until a new one is received over SACCH (i.e. active 3G-BA).
The Multi-RAT mobile is informed on how many WCDMA cells
(0-3) shall be reported in the measurement report. This is set by
parameter FDDMRR in command RLSUC. The remaining
positions will be used for GSM cells. Note that if multiple GSM
bands are used, there will be few positions in the measurement
report for cells from those bands, since only six cells can be
reported in the measurement report.
RLSUC:CELL=cell, …. FDDMRR=fddmrr;
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© Ericsson 2006
LZT 123 3801 R7A
2 Channel Concept
Within the measurement reports, WCDMA neighboring cells are
reported reusing the fields defined for GSM neighboring cell
measurements. For GSM neighbor cells, the RXLEV field is as
usual coded as the binary representation of the received signal
strength on the neighboring cell. For WCDMA neighbor cells, the
RXLEV field is instead coded as the binary representation of
CPICH Ec/No (Common Pilot Channel). Figure 2-17 illustrates
part of the Measurement Report.
For GSM neighbor cells, the BCCH-FREQ field is as usual coded
as the binary representation of the measured cell's position in the
BA list (BCCH Allocation). For WCDMA neighbor cells, the
BCCH-FREQ field is always coded as 31 (binary). This means that
the maximum number of GSM neighboring cells is reduced from
32 to 31 in cells having WCDMA neighboring cells defined.
A WCDMA cell is uniquely identified with its frequency and
scrambling code combination so there is no equivalent to BSIC for
GSM cells. In the field where BSIC is usually reported for GSM
cells, the binary representation of the measured WCDMA cell's
position in the active 3G-BA list is coded.
Measurement Result Message
(Serving cell measurements)
(6 bits) RXLEV- NCELL (GSM RSSI)
(5 bits) BCCH-FREQ-NCELL (BA list index)
GSM
Neighboring
(6bits) BSIC - NCELL
Cells
RXLEV-NCELL (CPICH
Ec /No)
BCCH-FREQ-NCELL = 31
WCDMA
RAN
Neighboring
BSIC-NCELL (3G BA list index)
Cells
.
.
.
Figure 2-17. Measurement Report
LZT 123 3801 R7A
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GSM BSC Operation
Upon receiving the measurements from a Multi-RAT MS, the BSC
continuously performs the locating algorithm in order to create a
candidate list for handovers. Measured WCDMA RAN and GSM
cells are processed separately. This is done by filtering out the
WCDMA RAN cell measurements before applying the GSM
locating algorithm. The GSM locating algorithm is modified in
order to process both WCDMA RAN and GSM neighboring cells,
as shown on Figure 2-18 below.
The existing GSM-GSM locating algorithm is kept intact. Parallel
with this, a GSM-WCDMA algorithm is performed based on the
traffic load of the serving cell and the measured WCDMA RAN
cell signal level. For filtering GSM measurements different filters
can be used. See Figure 2-18 for the Locating Algorithm
incorporating WCDMA.
WCDMA RAN Cell
Measurement
Filtering
Urgency Condition
Basic Ranking
Inter System
Handover
Algorithm
Traffic load
Add WCDMA Ran Cell to top of
The candidate list
Radio Network
Functions evaluations
Organizing the list
Sending the list
Allocation reply
Figure 2-18. GSM to WCDMA Handover Initiation
The key parameters that control handovers from GSM to WCDMA
are MRSL and ISHOLEV.
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© Ericsson 2006
LZT 123 3801 R7A
2 Channel Concept
•
•
MRSL defines a minimum threshold for the "quality" measure
Ec/No for handovers to WCDMA RAN. This parameter is
defined per WCDMA RAN cell.
RLDEC:CELL=cell, ….. MRSL=mrsl;
ISHOLEV, (Inter-System Handover Level) defines the traffic
load threshold of the serving GSM cell that needs to be
exceeded in order to evaluate WCDMA measurements for
handovers. The Inter-system handover evaluations start when
percentage of idle full rate traffic channels left in the cell is less
than or equal to this value given as percentage with values 0 to
99
RLLOC:CELL=cell, …… ISHOLEV=isholev;
Two criteria must be fulfilled for a GSM to WCDMA handover to
happen. The first criteria are that the percentage of idle TCHs in the
serving cell is less than the ISHOLEV parameter value. This will
happen only if the percentage of idle TCHs from the total number
of TCHs is equal to or lower than a threshold. This threshold is set
per GSM cell by the parameter ISHOLEV. Dedicated PDCHs are
regarded as busy traffic channels when evaluating the parameter
ISHOLEV. On-demand PDCHs are regarded as either idle or busy
depending on the setting of the Exchange property GPRSPRIO.
Traffic load in the serving cell is checked periodically. This period
is set per BSC with the exchange property COEXWCDMAINT.
Only when the first criterion is fulfilled, a second criterion is tested
separately for each neighboring WCDMA RAN cell.
This second criteria is that CPICH Ec/No is greater than MRSL
parameter value. To fulfill this criterion, the CPICH Ec/No must
exceed the threshold parameter MRSL set in the BSC and sent to
Multi-RAT MSs on the SACCH. All valid neighboring WCDMA
RAN cells (fulfilling the second criteria) are sorted in order of
decreasing CPICH Ec/No. A final candidate list is created by
adding WCDMA RAN cells on the top of the GSM candidate cells.
If an inter system handover fails, the parameter TALLOC is used to
prevent a new candidate list being immediately sent with the same
WCDMA RAN cell(s). The value of MRSL should depend on the
corresponding settings in the WCDMA RAN cell, in order to avoid
unwanted ping-pong effects. Also, MRSL should be set according
to FDDQMIN. For example, in order to balance the behavior in
active and idle mode, MRSL can have the same value as
FDDQMIN.
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GSM BSC Operation
ISHOLEV defines the main behavior of GSM-WCDMA
handovers. With ISHOLEV =99 (max. value), WCDMA will
always be prioritized. With different values of ISHOLEV,
handovers to WCDMA will be triggered only in case of high traffic
in the serving GSM cell. Therefore, a traffic off-load is achieved.
The parameter QSC (Qsearch_C) sets the threshold for the start of
WCDMA RAN FDD measurements in active mode. This parameter
has values of 0 to 15, which equate to values –98dBm to –54dBm
in 4dBm steps. The search for WCDMA RAN FDD cells is done
below the threshold level set.
RLSUC:CELL=cell, …. FDDQMIN=fddqmin, QSC=qsc;
Example 1: There is a requirement to off-load GSM traffic, and at
the same time extend WCDMA coverage. In this case ISHOLEV
should be set to the wanted traffic threshold, QSC should be set to
7 (always search for WCDMA cells), or to values 8-14 if the cells
are co-sited. This is because no GSM signal level criterion is
needed.
Example 2: There is a requirement only to extend WCDMA
coverage with GSM. ISHOLEV should then be set to 99 in order to
prioritize WCDMA all the time. Both QSC and QSI should be set
to 7, or 8-14 if the cells are co-sited. FDDQOFF can be set to 0
(Infinite, always select a WCDMA FDD cell if acceptable), since
all MSs are to be thrown back to WCDMA in idle mode as well.
If GSM coverage is to be extended with the WCDMA coverage,
QSC has to be used as a threshold below which WCDMA
measurements can start. In that case ISHOLEV should be set to 99.
Note: Bad quality from GSM cannot trigger handovers to
WCDMA if the traffic load criterion is not fulfilled in the GSM
cell.
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© Ericsson 2006
LZT 123 3801 R7A
3 BSS Configuration
3 BSS Configuration
Objectives:
Configure the BSS Subsytem using OSS RC or Winfiol
providing to the student the knowledge of the BSC, TRC and
BSC/TRC hardware as well as the interfaces to the MSC,
SGSN and RBS, and RBS2000 configuration.
ƒ Configure the Hardware and Interfaces of the BSC using MML
commands and parameters
ƒ Configure RBS 2000 equipment in the BSC using MML commands and
parameters
Figure 3-1. Objectives
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GSM BSC Operation
Intentionally Blank
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© Ericsson 2006
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3 BSS Configuration
BSC AND TRC HARDWARE OVERVIEW
The BSS architecture consists of the Transcoder Controller
(TRC), the Base Station Controller (BSC) without transcoder,
and/or a combination of both, the BSC/TRC, and the Radio Base
Station (RBS). See Figure 3-2.
A-bis
RBS
BSC/TRC
A
A-ter
A-bis
RBS
A-bis
RBS
BSC
MSC
A
TRC
A-ter
BSC
A-bis
RBS
Figure 3-2. The Modular and Flexible BSS System Architecture
•
•
•
LZT 123 3801 R7A
TRC - a Stand-alone transcoder controller node.
The TRC node allows a flexible location of the transcoder
resources. Typically, the TRC is located at or near the MSC. It
is controlled by the BSC.
BSC/TRC - a combined BSC and transcoder controller
The BSC/TRC is suitable for medium and high capacity BSC
applications, that is, urban and suburban area networks. This
node can handle up to 1,020, for R10 and below, Transceivers
(TRXs) a.k.a. Transceiver Units (TRUs) and 2000 for R11, a
so called Mega BSC.
BSC - a Stand-alone BSC without transcoders
The BSC is optimized for low and medium capacity BSS
networks and is a complement to the BSC/TRC, especially in
rural and suburban areas. For GSM 900/GSM 1800, it can
handle up to 1020/2000 TRXs/TRUs.
© 2006 Ericsson
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GSM BSC Operation
TRC
The Transcoder Controller (TRC) node contains the pooled
transcoder resources and is a stand-alone node. The TRC node
requires its own AXE 10 hardware platform components such as
APZ, IO, GSS, and TSS, as well as the transcoder hardware. See
Figure 3-3.
The TRC is connected to the MSC via the A-interface and to the
BSC via the Ater-Interface.
APZ
212 33
A
B
RPHRPH-A
APG 40
GEM
2 ET
19 TRA
GEM
2 ET
11 TRA
GEM
2 ET
14 TRA
16 RPG
16 RPG
16 RPG
16 RPG
16 RPG
16 RPG
7 RPP
7 RPP
Figure 3-3. BYB501 Cabinets for TRC
The TRC node has the ability to support up to 16 BSCs over the
Ater interface. The transcoders in the various TRAnscoder (TRA)
Pools in a TRC can be shared between all BSCs associated with the
TRC. One of the connected BSCs may be residing on the same
physical platform as the TRC, that is, in a combined BSC/TRC
network element.
One TRC can be connected to up to four MSCs. This makes it
possible to build rather large TRCs supporting several MSCs. One
BSC is still controlled by one specific MSC.
The TRC normally contains several transcoder resource pools, one
pool per type of transcoder. For example, Full Rate, Enhanced Full
Rate, Half Rate, AMR Half Rate and AMR Full Rate.
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© Ericsson 2006
LZT 123 3801 R7A
3 BSS Configuration
The A-interface signaling remains unchanged in the new system
structure. For communication between the TRC and a remote BSC
a C7 based Ericsson proprietary communication protocol is used.
In the case of a combined BSC/TRC, internal signaling between
the TRC and the BSC part is used.
The TRC node handles the Ater transmission interface resources.
The operation and maintenance signaling and handling of the Ater
interface (that is, Block/Ack, Unblock/Ack, Reset Circuit/Ack and
Unequipped Circuit) is similar to the current implementation on the
A-interface.
At call set up and after signaling connection set up, an assignment
request is sent via the MSC to the BSC. The request is sent directly
to the BSC and can pass transparently through the TRC. The BSC
receives the assignment request and requests a transcoder device
from the TRC, also indicating the A-interface Circuit Identification
(CIC) to be used for this specific call. The TRC allocates a
transcoder device and the time slot on the Ater interface, which is
connected to the A-interface CIC, specified by the MSC. The TRC
replies to the BSC, which establishes the connection to the mobile.
TRC hardware is shown in Figure 3-4.
RALT
RTLTT
ETC
ETC
ETC
ETC
MSC/VLR
BSC
GS
TRAU
RP
ST7
SRS
RPG
RP
SP
RP
RP
RP
CP
Figure 3-4. TRC Hardware
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GSM BSC Operation
BSC/TRC
The BSC/TRC is a combined BSC and TRC node. The transcoders
are set up on a per call basis, which implies a more efficient use of
the transcoder resources. It is still possible though to have
Transceiver Groups (TGs) with semi-permanently connected
Transcoder and Rate Adaptation Units (TRAUs) in the
BSC/TRC. The BSC/TRC is suitable for medium and high capacity
BSC applications, that is, more than 256 TRXs. The addressing
capacity of the BSC/TRC is 1,020 TRXs.in R10 and 2000 in R11.
Cost efficient networks can be built by connecting remote BSCs to
the BSC/TRC. Up to 15 remote BSC nodes can be connected to a
BSC/TRC and the capacity is more than a total of 1,020 TRXs for
the BSC/TRC and its remote BSCs.
A high capacity BSC/TRC has several advantages:
• It reduces the load on the MSC due to fewer inter BSC
handovers and it is less sensitive to traffic peaks in a particular
area.
•
•
A high capacity BSC/TRC is more suitable for dual band
operation (GSM 900/1800) than a low capacity BSC.
With fewer nodes to handle, the operation and maintenance
costs will decrease.
Back
Front
APZ
212 33
A
B
RPHRPH-A
APG 40
GEM
2 ET
19 TRA
GEM
2 ET
11 TRA
GEM
2 ET
14 TRA
16 RPG
16 RPG
16 RPG
16 RPG
16 RPG
16 RPG
7 RPG
7 RPG
Figure 3-5. BYB501 Cabinets for BSC/TRC
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© Ericsson 2006
LZT 123 3801 R7A
3 BSS Configuration
For a BSC/TRC site handling up to 250-300 TRXs, two cabinets
are needed, and for a full scale BSC/TRC supporting up to 2000
TRXs, tree to four cabinets are needed. Hardware layout for
BSC/TRC using BYB501 is illustrated in Figure 3-5.
In the BSC/TRC, ordinary Exchange Terminal Circuits (ETCs)
are used as the interface to both the MSC and the RBS. The
transmission path for speech and signaling is over a 1.544 (T1) or
2.048 (E1) Mbps PCM link. Speech is switched through the Group
Switch (GS), in the BSC. See Figure 3-6.
The Subrate Switch (SRS), part of the Group Switch Subsystem
(GSS), is used to perform Link Access Protocol on D-channel
(LAPD) concentration and multiplexing.
For signaling towards the MSC, Base Station System Application
Part (BSSAP) messages are transferred using the Message
Transfer Part (MTP) protocol, transparently through the TRC.
MTP utilizes a C7/SS7 signaling terminal connected to a PCM
channel (the physical link).
Signaling between the BSC/TRC and the transceivers utilizes a
Transceiver Handler (TRH) device, which transforms signaling
to LAPD format.
MSC
BSC/TRC
RBS
RALT
ETC
ETC
ETC
ETC
RBLT
ETC
GS
ETC
TRAU
S7-ST
SRS
RP
RPG
RP
CP-A
RP
TRH
RPG RP
RP
SP-A
Figure 3-6. BSC/TRC Hardware and interfaces
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GSM BSC Operation
BSC
The stand-alone BSC is developed and optimized especially for
rural and suburban areas and is a complement to the BSC/TRC
node in the BSC product portfolio.
The BSC contains the SRS and the TRH. It requires its own AXE
810 hardware platform components, such as APZ, IOG or APG,
GSS, and TSS.
The BSC does not contain any transcoders. It utilizes transcoder
resources from a central BSC/TRC or from a TRC node. The BSC
is connected to the BSC/TRC or TRC via the Ater interface. It can
be remote controlled from the OSS.
Hardware layout for BSC is shown in Figure 3-6.
APG40
CPUM
GEM
GEM
Figure 3-7. BYB501 Cabinets for BSC
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© Ericsson 2006
LZT 123 3801 R7A
3 BSS Configuration
AXE810 BSC / TRC HARDWARE
AXE 810 incorporates a number of new hardware components into
the BSC/TRC to improve the performance, capacity and footprint
of the nodes and to standardize the IO specifications. The CP, IO
system and the Group Switch are all improved and the APT 1.5
hardware is introduced.
The APZ 212 33C is a compact but powerful APZ Central
Processor, housed in a single subrack and providing sufficient
capacity for all types of BSC. APZ 212 33 utilises the high speed
IPN 100 Mbits/s fast Ethernet communication towards the IO
system to reduce the times required for backup and reload.
RPBI-S
RPBI-S
RPBI-S
IPNAX
POWC
SPU
IPU
DSU-D
DSU-D
(BRU)
MAU
(BRU)
DSU-D
DSU-D
IPU
POWC
SPU
IPNAX
RPBI-S
RPBI-S
RPBI-S
It is used in all new BSC and BSC/TRC nodes in combination with
BYB 501/AXE 810 and APG 40.
Figure 3-8. APZ 21233C
APG40 is the default IO system used in AXE switches and it is
supported as the IO System for BSC/TRC. APG40 provides the
following benefits:
•
•
•
•
LZT 123 3801 R7A
An IO Platform for future applications
Increased Processor capacity compared to IOG20
Increased STS counter throughput from CP to IO, as much
as 1 000 000 counter values in 5 minutes.
Use of standard TCP/IP communications
© 2006 Ericsson
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GSM BSC Operation
•
Up to 10 times increased data throughput CP – IO
compared to IOG20
Figure 3-9. APG-40/C2
APT 1.5 hardware incorporates the GS890 Group Switch, specific
APT hardware including Transcoder R6, ET155-1 and RPG3 as
well as an interface to allow existing BYB501 hardware devices to
connect to GS890. This Group Switch has a distributed architecture
and is incorporated in the GEM subrack (Generic Ericsson
Magazine).which houses the APT hardware.
The layout of subracks incorporating AXE810 hardware is shown
in Figure 3-10. RPPs required for High Speed Signaling Links and
Packet Control Unit (PCU) shown in the optional subracks in
Figure 3-10, are implemented using BYB501 hardware and are
connected to the Group Switch in one of the GS890 subracks via
the DLEB (Digital Link multiplexer for Existing equipment
Board). RPG3 in the BYB501 subracks are also connected to the
Group Switch via DLEB and are used for TRH, C7ST and STC
(RBS 200).
•
•
•
- 72 -
© Ericsson 2006
An example of a High Capacity R10 BSC /TRC for up to
1000 TRXs
Up to 6000 Erland
Up to 504 E1/T1 links (in 8 ET155-1)
LZT 123 3801 R7A
3 BSS Configuration
Basic
Options
RPG-3
(GS890)
(TRA)
RPP
(RPG-3)
(RPG-3)
2 ETC
APG40
AP Z
212 33C
RPP
GS890
TRA
GS890
(ET155-1
GS890
(ET155-1
RPP
RPP
RPG3
RPP
RPG3
RPP
RPG3
HSL/ET C
RPG3
Figure 3-10. AXE810 BSC/TRC High Capacity Hardware
Where each Subrack AXE 810 has the common layout as follows:
Figure 3-11. AXE810 GEM Subrack
GEM is short for Generic Ericsson Magazine. In its basic configuration, the
GEM contains a duplicated 16 KMUP Group Switch and a duplicated
regional maintenance processor. The GEM provides physical space for up to
241 different devices which basically can be freely mixed. (1) 22 switch
devices
The magazine is designed for full size PBA ROJ 208.
LZT 123 3801 R7A
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GSM BSC Operation
• SCB-RP_A/B maintenance processor (ROJ 208 323/1), Plane A/B
• XDB_A/B 16K MUPs (ROJ 208 304/1) Plane A/B
• 22 generic device slots (1 - 22)
The AXE 810 can be extended up to 32 subracks. A normal BSC will
have about 4 GEM + a number or GDM subracks in all. The
maximum is shown in fig 3-12.
Figure 3-12. AXE810 maximum GEM Subrack configuration
Typical AXE 810 PIU in BSC/TRC are TRAU R6 (or TRAU R6B)
and ET155-1
PIU such as RPG3 which has a higher capacity, compared with
RPG2, used for TRH and C7ST2 are allocated in GDM (BYB 501).
The RPG3 is only half the size of the RPG2 though.
RPG2 can handle 24 TRX each but RPG3 can handle 32 TRX each.
In the event of RBS200 the RPG2 can replace 8 STC but RPG3 as
many as 12.
RPP for PCU and HSL are also still in GDM.
The GDM are connected via DLNB in AXE810 GSS 890 as in figure
3-13 below.
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© Ericsson 2006
LZT 123 3801 R7A
3 BSS Configuration
2 Mbps
ETC5
GSS
890
XNB
D
L
N
B
155
Mbps
ET155-7
GSS
501
501 HW
kept and
adapted to
AXE 810
Other Devices
RPG2
GDM
2 Mbps
ETC5
GSS
890
155
Mbps
ET155-1
XDB
Extensions
with
AXE 810
& GDM based
equipment
TRA R6
GDM
RPG3
Figure 3-13. NNRP-4 GS Conversion
High Speed Links for both ETSI and ANSI are now supported. Each link only
requires 1 RPP and a 2 (1,5) Mbps PCM link and it replaces approximately 16
CCITT #7 links as shown in figure 3-14.
16 C7/SS7 links
MSC
BSC/TRC
HSL
MSC
BSC/TRC
Figure 3-14. HSL (High Speed Signaling Link)
Figure 3-15. RP in AXE 810 (RPP, RPG3 and RPI)
LZT 123 3801 R7A
© 2006 Ericsson
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GSM BSC Operation
•
•
•
- 76 -
© Ericsson 2006
PCU (GDM based) PCI based RP used for PCU (GPRS)
and HSL (High Speed Link) for signaling
RPG3 (GDM based) RP with GS interface used for TRH,
#7 signaling and STC (RBS 200) This is half the size of
RPG2 but with higher capacity.
RPI (GEM based) Integrated RP on AXE 810 boards used
for handling the devices on the board.
LZT 123 3801 R7A
3 BSS Configuration
DEFINITION OF NODE TYPE
The purpose of the function is to define the node type. The node
type is by default the BSC/TRC physical node. The operator can
change node types by command. Four possible transitions are
supported, as described below.
BSC/TRC TO BSC
This function supports the change of node type from a BSC/TRC
physical node to a BSC physical node.
This node type change will not be allowed if there are external
BSCs connected to the node. The Circuit Identity Code (CIC) for
all A-interface and Ater interface devices must be removed. In
addition, all transcoder devices must be in the pre-post Service
State.
When changing node type to BSC physical node it is necessary to
specify the Destination Point Code (DPC) of the associated TRC.
Concerning CCITT signaling the Network Indicator must also be
specified. The Network Indicator is not required for ANSI
signaling.
BSC/TRC TO TRC
This function supports node type change from a BSC/TRC physical
node to a TRC physical node.
This node type change will not be allowed if there are any
transceiver groups defined. The CIC for all A-interface devices,
used by the BSC in the BSC/TRC physical node, must have been
removed. In addition, all Abis interface devices must be in the prepost Service State.
BSC TO BSC/TRC
This function supports node type change from a BSC physical node
to a BSC/TRC physical node.
This node type change will not be allowed unless the CICs for all
Ater interface devices are removed.
LZT 123 3801 R7A
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GSM BSC Operation
TRC TO BSC/TRC
This function supports node type change from a physical TRC to a
BSC/TRC physical node.
This node type change will not be authorized if a maximum of 16
BSCs is connected to the TRC physical node.
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© Ericsson 2006
LZT 123 3801 R7A
3 BSS Configuration
NODE TYPE PARAMETERS
This table outlines the parameters, which are defined in each node
type, to enable a setup of the new separated system.
Node Type
Parameter
BSC
TRC
BSC/TRC
Node Type
Yes
Yes
Default(1)
A-CIC
-
Yes (RALT)
Yes (RALT)
Ater-CIC
Yes (RTLTB)
Yes (RTLTT)
Yes(RTLTT)(2)
BSC name
-
Yes
Yes(3)
DPC
TRC, MSC
BSC(s)
MSC, BSC(s)
Signaling
(ANSI, CCITT)
A, Ater
Ater
A, Ater
Transmission
24/32 channel
Ater
A, Ater
A, Ater
Table 3-1. Parameter Definition Based on Node Type
1. When the system is initially set up, the node type is defined as
combined BSC/TRC as default.
2. The RTLTT/RTLTT24 devices will have Ater CIC defined in
the combined BSC/TRC node for external BSC(s) connections
only.
3. The BSC name will be defined in the combined BSC / TRC
node for external BSC(s) connections only. Internal BSC will be
automatically defined by the name ‘own’.
Different device types between the Nodes on the interfaces are
shown in Figure 3-16.
LZT 123 3801 R7A
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GSM BSC Operation
ALT
MALT R
BSC/
TRC
RTLTT RTLTB
BSC
TRC
RTLTT RTLTB
BSC
RBLT
RBS
MSC
MAL
T
RAL
T
RBLT
RBS
Figure 3-16. Device Types
STAND-ALONE BSC NODE
For the stand-alone BSC node the node type is set by the command
RRNTC. The Destination Point Code (DPC) for the TRC and the
Network Indicator (NEI) for CCITT signaling are also set by the
new command. The DPC is set for ANSI signaling.
The Ater Circuit Identity Code (CIC) is set for the RTLTB
/RTLTB24 device using the updated command, RACII.
The commands to set the destination point for the MSC are RADPI
and RADCI.
STAND-ALONE TRC NODE
The stand-alone TRC is defined using the command RRNTC. The
command RRBSI defines a BSC in a TRC. The command specifies
the BSC and the DPC of the BSC to be connected and the Network
Indicator (NEI) for CCITT signaling is also set by the new
command.
The command RACII is used to define the Ater TRC devices with
an Ater CIC and the BSC connected. In addition, this command
defines the A-interface devices with a CIC and the connected BSC.
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© Ericsson 2006
LZT 123 3801 R7A
3 BSS Configuration
COMBINED BSC/TRC NODE
For the combined BSC/TRC node the node type is set using the
command RRNTC. The command RRBSI defines a BSC in a TRC.
Combined BSC/TRC is the default node value.
The A-interface devices are connected using the updated command
RACII. If the BSC name is omitted or given as "own" in the
command, the BSC is internal to the combined BSC/TRC. The CIC
for the RALT device and the RTLTT / RTLTT24 device are also
specified in the command RACII. The commands to set the DPC
for the MSC are RADPI and RADCI.
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GSM BSC Operation
BSC AND TRC SPECIFIC HARDWARE
TRANSCODER RATE ADAPTATION UNIT (TRAU)
The transcoder (TRA) is located in the TRC (it can also be located
in the BSC/TRC). The TRA is controlled by a Regional Processor
and, in active state, is also controlled by the Radio Base Station via
inband signaling.
The transcoder receives data down-link from the A-interface and
passes it on to the Abis interface and vice versa. In the stand-alone
TRC, the transcoder passes data onto the Ater interface towards the
remote BSC. The PCM speech samples, received from the Ainterface, are first compressed into TRA speech frames before
being sent down to the Base Station over the Abis interface. The
TRA speech frames received up-link from the Base Station are
decompressed and converted to PCM speech samples before being
forwarded to the MSC over the A-interface. V.110 data frames,
received from the A-interface, are mapped onto the TRAnscoder
and rate Adaption Unit (TRAU) frames on the Abis interface and
vice versa.
TRA functions include:
• Transcoding of speech information. Speech at 64 kbps to/from
the MSC is transcoded to 13 kbps towards the RBS enabling
four compressed channels to be multiplexed onto one 64 kbps
channel.
•
•
•
- 82 -
Additional control information (3 kbps) is added to the
transcoded rate of 13 kbps towards the RBS giving a final
output of 16 kbps.
Rate adaptation of data information (maximum data rate
supported at present in GSM is 14.4kbps).
DTX functions on the up-link, which allows the mobile radio
transmitter to be powered down most of the time during speech
pauses.
© Ericsson 2006
LZT 123 3801 R7A
3 BSS Configuration
RBLT
RBS
ETC
GS
MSC
RALT
ETC
TRH
TRAU
TRAB
SRS
Figure 3-17. SRS / TRAU / TRH Interworking Block Diagram
The TRA function performs encoding and decoding of speech and
rate adaptation of data. It multiplexes a number of TCHs onto one
64 kbps channel improving transmission efficiency between the
BSC and the BTS. This transmission efficiency is further improved
through the use of the Subrate Switch (SRS). Figure 3-16 illustrates
circuit connection through the BSC/TRC utilizing TRA and SRS at
block diagram level.
Speech codecs for Full Rate (FR), Half Rate (HR), Enhanced Full
Rate (EFR), Adaptive Multi Rate Full Rate (AMR-FR) and
Adaptive Multi Rate Half Rate (AMR-HR) are all supported. A
speech codec is a combination of a channel rate and a speech
version.
EFR is the full rate codec using speech Algorithm version 2 for
GSM. EFR offers better speech quality compared to FR.
FR is the speech codec type using Algorithm version 1. Only this
can be seized for semi-permanent connections.
The HR speech codec uses Algorithm version 1 and offers
increased TCH capacity, twice the number compared to FR.
AMR is a new speech codec type defined for GSM. It consists of a
number of different codecs, which together with the associated
channel coding have been optimized for different radio
environments. Usage of AMR provides a significant improvement
in speech quality over other codecs by selecting the best speech
codec rate for current radio conditions. It is using algorithm version
3.
LZT 123 3801 R7A
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GSM BSC Operation
TRANSCODING AND RATE ADAPTATION
Table 3-2 below illustrates the combinations for HR, FR, EFR,
AMR-FR and AMR-HR transcoders.
Codec Type
S/D Rate
Signaling Rate
Channel
Rate
Speech
Algorithm
Half Rate
6.5 kbps
1.5 kbps
8 kbps
1
Full Rate
13 kbps
3 kbps
16 kbps
1
Ext. Full Rate
13 kbps
3 kbps
16 kbps
2
AMR Full Rate >12.2 kbps
< 0.8 kbps
16 kbps
3
AMR-Half Rate >7.4 kbps
< 0.6 kbps
8 kbps
3
Table 3-2. Codec Transcoder
AMR consists of a number of different codecs, one of which is
selected depending on the measured Channel Interference Ratio (C/I)
conditions. Eight speech codecs are defined for AMR. Six of these
have been defined for use in half rate channels, but only five are
supported. The amount of channel coding is increased significantly
when a codec is used in a full rate channel. Table 3-3 illustrates the
codec rates for AMR FR and AMR HR.
Channel Mode
AMR FR TCH
AMR HR TCH
Source Codec Bit Rate
12.2 kbps (GSM EFR)
10.2 kbps
7.95 kbps
7.40 kbps (IS 136 EFR)
6.70 kbps
5.90 kbps
5.15 kbps
4.75 kbps
7.95 kbps (not supported)
7.40 kbps
6.70 kbps
5.90 kbps
5.15 kbps
4.75 kbps
Table 3-3. AMR Full Rate and Half Rate
TRA R5 HARDWARE
TRA R5 is a re-configurable Digital Signal Processor (DSP)
hardware platform based on low voltage technology. One subrack
as shown in Figure 3.18 below houses 16 Transcoder Boards
(TRABs). These boards may be used for different types of codec
applications by loading the boards with different software.
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CONFIGURATION
A subrack houses 16 TRA EMs (16 TRABs), two RPs, and two
Digital Link Half height Boards (DLHBs). The TRA EMs are
full height PCBs while the other units are half height PCBs. There
are 24 channels per EM, thus one subrack supports up to 384
TCHs.
An LED for fault indication is mounted in front of each TRAB.
The LED is controlled by the Central Processor. A lit LED
indicates a faulty TRAB.
R5B is needed for AMR.
DLHTRAT
TRA R5 and R5B Subrack (front view)
R D
L
P
H
4- B
0 A
TRAB x 16
TSM
TSM
GS
Plane A
Plane B
D R
L P
H 4B 1
B
Plane A and B are
separated in theSNTs.
Figure 3-18. The TRA R5 and R5B Subrack
AMR can not be used in RBS 200 or 2301 though
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GSM BSC Operation
TRA R6 HARDWARE
SCB
XDB
CGB
TRA
TRA
TRA
TRA
DLEB
IRB
ET155
ET155
TRA
CGB
TRA
TRA
TRA
DLEB
IRB
TRA
TRA
SCB
XDB
ET155
ET155
Transcoder hardware TRA R6 is part of the AXE 810, using the
BYB 501 building practice and is located in the Generic Ericsson
Magazine (GEM) magazine as shown in Figure 3-19 below.
Figure 3-19. TRA R6 in GEM
The TRA R6 supports all coding schemes.
MULTIPLEXING AND DEMULTIPLEXING OF CHANNELS
The transcoder multiplexes a number of transcoded channels into
one 64 kbps channel, used between the BSC and BTS. The number
of multiplexed channels depends on the type of speech codec:
• 4 traffic channels for FR or EFR.
•
8 traffic channels for HR.
In terms of hardware, a TRA-R5 EM consists of 32 devices,
requires 32 GS inlets and can handle 24 TCHs.
A TRA-R6 EM consists 256 devices, requires 256 GS inlets and
can handle 192 TCHs.
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TRAU 4 & 5 FR/HR
TRAU 6 FR/HR
0
1
2
3
4
5
6
7
8
9
10
11
12
0
1
2
3
4
5
6
7
8
9
10
22
23
24
25
26
27
28
29
30
31
Coded
Uncoded
Uncoded
Uncoded
Uncoded
Coded
Uncoded
Uncoded
Uncoded
Uncoded
Coded
“
“
Coded
Uncoded
Uncoded
Uncoded
Uncoded
Coded
Uncoded
Uncoded
Uncoded
Uncoded
0
1
2
3
4
5
6
7
8
9
10
11
12
22
23
24
25
26
27
28
29
30
31
Coded
Uncoded
Uncoded
Uncoded
Uncoded
Uncoded
Uncoded
Uncoded
Uncoded
Coded
“
“
Coded
Uncoded
Uncoded
Uncoded
Uncoded
Uncoded
Uncoded
Uncoded
Uncoded
20
21
22
23
24
25
26
27
38
29
30
31
Coded
Uncoded
Uncoded
Uncoded
Uncoded
Uncoded
Uncoded
Uncoded
Uncoded
Coded
“
“
Coded
Uncoded
Uncoded
Uncoded
Uncoded
Uncoded
Uncoded
Uncoded
Uncoded
–
-
0
1
2
3
4
5
6
7
8
9
10
20
21
22
23
24
25
26
27
38
29
30
31
Coded
Uncoded
Uncoded
Uncoded
Uncoded
Uncoded
Uncoded
Uncoded
Uncoded
Coded
“
“
Coded
Uncoded
Uncoded
Uncoded
Uncoded
Uncoded
Uncoded
Uncoded
Uncoded
–
-
Figure 3-20. TRAB Configured for FR/EFR
The relationship between a TRA-EM and an SNT is 1 to 1. .
The connection and disconnection of a transcoder devices to and
from an SNT is performed via commands. In addition, a printout of
transcoder device states and transcoder-SNT connections can be
obtained by command.
Before transcoder equipment can be seized for a connection
towards the BTS, it must be physically and logically connected,
and manually deblocked. After that they are included in the pool
for which they have been configured.
The pools are Pooled transcoder devices are seized according to
TRA capability and availability. The connections through the GS
for a transcoder device seized in a pool are set up on a per call
basis. The Subrate Switch is required for pooled transcoder use.
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GSM BSC Operation
TRA HARDWARE
There are number of revisions of TRA hardware in use in
GSM networks. Each type has its own name depending on speech
version as shown in table 3-4 below.
Rev
Name
SNT
SAE
Speech
R4
RTTF1D
RTTF1S
969
RTTF2D
RTTF2S
970
Full
Enhanced
RTTH2D
RTTH2S
971
Half
RTTF1D1
RTTF1S1
995
RTTF1D2
RTTF1S2
RTTH1D
RTTH1S
996
104
Full
Enchanced
RTTAF1D
RTTAF1S
R5
R5
R6
114
RTTAH1D RTTAH1S 114
110
RTTGD
RTTGS
Half
AMR Full
AMR half
All
Table 3-4. TRA Hardware
Administration Of Transcoder Pools
A transcoder pool is identified by its name. The pool may only
contain resources of the same channel rate and speech version. The
administration of transcoder pools can be divided into these parts:
•
•
Defining transcoder pools
•
Changing the number of transcoder resources
•
Deleting transcoder pools
Printing transcoder pool administration details
Defining Transcoder Pools
A new pool can be defined. A pool must contain the same codec
type. There are four codec types: FR, EFR, HR, AMR-FR and
AMR-HR. In the future it will be possible to support up to 32
different types.
Deleting Transcoder pools
Prior to deleting a pool, the number of transcoder channels must be
set to zero and pool supervision must be deactivated.
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Changing a Transcoder Pool
This allows the number of pool transcoder resources to be changed.
Before any changes can be made, the transcoder pool supervision
must be deactivated.
Printing Transcoder Pool Administration Details
This printout will reveal the pool name, channel rate, speech
version, required number of transcoder resources, actual number of
transcoder resources, number of idle transcoder resources, number
of resources used in traffic, and transcoder devices. The command
RRTPP:TRAPOOL=ALL; can be used for this
Operational Instructions
Radio X-ceiver Administration, Transcoder and Rate Adapter to
SNT, Connect.
Radio Transmission Transcoder Pool, Initiate/Change/End.
Selconfigurating TRAPOOLS
TTRAREQ
TTRAEX
MINPOOLSIZE
TTRAREQ
TTRAEX
MINPOOLSIZE
Figure 3-21. Selfconfigurating TRAPOOLS
Activation and Selection of mode is done with cmd RRPSI
–
Ex: RRPSI: RECMODE=DEL, RECTIME=0300, NUMDAYS=7;
This is a delayed reconfiguration that takes place every week at 0300
hours on the night it started. I.e. every 7 day.
Setting of thresholds is done per transcoder pool
– Example: RRPSC: TRAPOOL=FRPOOL,
TTRAEX=40, MINPOOLSIZE=240;
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GSM BSC Operation
This means the minimum poolsize for this FR pool must not go below
240 devices and it requires more capacity if the idle level has been
below 10% and it can surrender resources.
TRH (RPG 2)
TRH, based on an RPG2, can handle up to 24 TRXs. However, the
CPU Capacity in the RPG2 can be a limiting factor. If the function
TRH Load Distribution is not used, the number of TRXs possible
to connect to one RPG2 based TRH, is 16. Otherwise the limit
depends on the traffic model.
•
There are 7 specific EM programs loaded in the TRH
– RHLAPDR
– RHSNTR
– RMPAGR
– RCSCBR
– RQRCQSR
– RQUNCR
– RCLCCHR
The TRH serves LAPD-links to both RBS 200 and RBS 2000. The
hardware consists of one PIU The RPG2 allows interaction
between different regional software programs without CP
involvement.
TRH (RPG3)
TRH, based on an RPG3, can handle up to 32 TRXs.
It is half the size of a RPG2 and therefore we can have 16 in one
GDM in BYB 501.
Operational Instructions
Transceiver Handler to Group Switch Connect
RPD EM connect
There are one detail to remember here though, the RP must be
blocked when the EMs are deblocked even though FC=17 is
received. When all EMs are CBL and the RP is deblocked all EM
goes working.
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THE SUBRATE SWITCH (SRS)
The Subrate Switch is an extension to the Group Switch. It is used
in all node types, that is, TRC, BSC/TRC, and BSC. The purpose
of the Subrate Switch is to allow for communication between
devices at rates less than the standard 64 kbps. Subrate
transmission is permitted from 8 kbps to 56 kbps in increments of 8
kbps. This makes it possible to switch devices from different
transcoders to the same Exchange Terminal Circuit (ETC)
device.
The subrate solution in the new GS890 is implemented in the first
row of the switch. This row has the capacity of 128K and the same
hardware can be used for both subrate and normal rate. However, if
the subrate function is used, the maximum size of the switch is
limited to 128K. This size should be enough for any type of BSC
implementation. The figure below shows the part of the switching
matrix where subrate can be used.
0-0
0-1
0-2
0-3
0-4
0-5
0-6
0-7
1-0
1-1
1-2
1-3
1-4
1-5
1-6
1-7
2-0
2-1
2-2
2-3
2-4
2-5
2-6
2-7
3-0
3-1
3-2
3-3
3-4
3-5
3-6
3-7
Figure 3-22. Subrate in GS890
The maintenance function of the SRS contains one autonomous
and one manual part. The autonomous part discovers erroneous
behaviors in the SRS hardware and presents them to the operator.
The manual part enables the operator to replace the faulty hardware
and maintain the unit.
The SRS is size alterable by command in BYB202 and BYB501
hardware configuration and may be configured in eight stages of
0.5 K to a maximum of 4 K in size. In the AXE810 BSC, the
maximum size of the SRS is 128K and the hardware is
incorporated in the XDB board in the GEM subrack. The minimum
allocation is 16K.
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GSM BSC Operation
The subrate switching mode is set when defining the group switch
with command GDCOI.
Path Setup
•
•
Both-way on-demand subrate connection.
Both-way on-demand connection between sub-MUltiple
Positions (sub-MUPs) is available. Used at call setup for halfrate and full-rate calls for pooled TGs.
One-way on-demand subrate connection.
One-way on-demand connection between sub-MUPs is
available. This is used at handover to setup a one-way downlink connection to the new time slot (or half time slot for halfrate) simultaneously as the both-way connection for the old
connection is kept, before a switch to the new connection is
performed. (For intra cell - inter cell - intra BSC handover).
•
Note: One-way connection is not used in the SRS. A handover
of a one-way connection is performed between RALTDEMUX.
Loop connection.
Loop connection (the same incoming and outgoing sub-MUP)
is available. This is used for pooled TGs to connect a loop on
16 kbps (time slot level) for an idle time slot on the Abis
interface. It is used for looping back a synchronization pattern
from the BTS on the time slot level.
Disconnection
Disconnection of subrate connections is handled by the user at the
disconnection of a call for on-demand connections or in a fault
situation for semi-permanent subrate connections. At
disconnection, sub-MUPs data bits are set to the value of the
corresponding idle pattern bits. The GS starts sending a pre-defined
idle pattern.
Handover
A path through the GS can be re-arranged. This means that for a
both-way connection, established between sub-MUPs A and B, a
subrate path change can be made to sub-MUP C, resulting in a
both-way connection between A and C. The subrate handover
process in GSS consists of:
•
- 92 -
Establishing a one-way connection from A to C.
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3 BSS Configuration
•
•
Converting paths to obtain a one-way connection from A to B
and a both-way connection between A and C.
Releasing a one-way connection from A to B.
Step 2 of the process is introduced to support the handover
function. As long as a one-way connection exists, toggling between
paths is allowed. Each process part is ordered by the user.
Connection/disconnection of an SRS Unit to the GS
After an SRS has been connected to the GS, an alarm will indicate
that the newly connected SRS is manually blocked. Manual
deblocking must be performed before the SRS unit can be used.
The SRS must be manually blocked, and other devices connected
to the SRS must be disconnected, before disconnection of the SRS
can be executed. After the SRS is disconnected, the previous
manual blocking alarm for the SRS ceases.
The BYB501 SRS utilizes a SNT connections to the Group Switch
at DL3 level. As previously mentioned, AXE810 SRS is configured
on the same hardware (XDB) as the distributed Group Switch in
the GEM. -The SRS, following the SNT concept, has an SNT type
SNTSRS, and is indicated by a variant.
Commands
NTCOI:SNT=SRS-n,SNTP=sntp,SNTV=sntv;
For connecting the SRS unit to the TSM.
NTCOE:SNT=SRS-n;
For disconnecting the SRS from the TSM.
NTCOP:SNT=SRS-n;
For printing the SRS unit's connection information.
NTBLI:SNT=SRS-n;
For manually blocking an SRS unit on both planes.
NTBLE:SNT=SRS-n;
For deblocking an SRS unit.
NTSTP:SNT=SRS-n;
For printing the current blocking state of the SRS unit.
NTTEI:SNT=SRS-n;
For initiating a test of the SRS unit.
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GSM BSC Operation
Mobile crosstalk Control (MCC)
This feature is a specially designed algorithm reducing the echo,
generated from mobile phones.
It provides the possibility to load MCC software in the transcoder.
Integrating the SW in the TRA reduces echo in intra-PLMN MSMS. It can be implemented in a combined BSC/TRC node, or in a
stand-alone TRC node. It reduces the acoustic echo generated in
the mobile phones - see Figure 3-23. The end users will perceive an
enhanced speech quality. So far it has been implemented in the GMSC, but from R8 it will be implemented in the transcoder by
means of a specially designed algorithm. A benefit of implementing
MCC in the transcoder is that it will also work for intra- PLMN,
MS-MS calls.
ECP
16/64 mS
Delay
100 mS
MSC
BSC
Delay
TRA
Figure 3-23. Mobile Crosstalk Control
When using transcoder type R4 configured for enhanced full-rate
(EFR) with this feature turned on, the capacity is reduced from 24
to 20 transcoders per device.
When using transcoder type R5 and R5B there will be no capacity
reduction. All supported APZ versions, BYB 501 and/or BYB202
can be used with this feature. No new HW is required. In TRA R5
and R5B, FR EFR and HR can be used with MCC. In TRA R4, FR
and EFR can be used with MCC.
Transcoder R6 also supports the function for all TRAU types.
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MCC ALGORITHM
Echo Canceller Description
The basic function of an echo canceller is to subtract the echo from
the near end, PSTN, speech. This is performed by creating a model
of the speech, sent from the mobile side. The model is stored in an
FIR filter. The FIR model is then used to subtract the generated
echo. The remaining echo is suppressed by the non-linear processor
(NLP). The double talk detector (DTD) switches off the NLP
completely when DT talk is detected. A tone detector (TD) disables
the echo canceller for data/fax communication.
Basic functionality: The echo canceller is located in the GMSC and
is inserted towards the PSTN. The Ericsson GSM system can have
pool and/or trunk echo cancellers. Echo cancellers in pool means
that the cancellers are treated as a common resource where a
canceller device is selected, if needed. The echo canceller in pool,
is connected directly to the group switch. The trunk echo canceller
is installed on trunk bases. If the trunk echo canceller is not needed
it is disabled with control from the AXE, or from time slot 16
signaling.
Mobile Cross-talk Control Function: Mobile Cross-talk Control
(MCC) is an optional function specially designed to handle the MS
echo problem. It operates in the same way as an ordinary echo
canceller but it is directed towards the mobile station and it is
specially designed to cancel the non-linear acoustical echo
generated in the mobile.
The ECP323 product, obtained by loading the ECP 323 DSP DSU
on the ECP 303 HWP and with the ECP Software (SW) in AXE, is
a network echo canceller removing the echo originated in the
PSTN network, and simultaneously featuring the MCC function.
The ECP 404 HWP can likewise be converted to ECP424.
In addition, the MCC functionality is available in the transcoder
device. This requires TRA R4 or higher (TRA R4 HR excluded).
The advantage is that the MCC function will be present even in a
mobile to mobile call.
If MCC is available both in the EC and in the TRA, a call could
end up with two MCCs in tandem. This will, however, not cause
any problems since the MCC function can be enabled in both the
EC and the TRA.
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GSM BSC Operation
A-INTERFACE
GSM 900/GSM1800
The PCM links of the A-interface (TRC-MSC or TRC/BSC-MSC)
are terminated on ETCs in the TRC/BSC and are controlled by
RALT software - see Figure 3-24. Both speech and data channels
(each 64 kbps) on the links are defined as RALT devices. The C7
signaling channel is connected semi-permanently through the GS.
The incoming channels on the A-interface from the MSC are
switched in the GS to speech coded channels over the A-bis
interface. The C7 signaling path is provided by an RPG which
interfaces the GS directly and from there via a semi-permanent
connection the signaling link.
GS
ETC
MSC TRC/BSC
C7
ST2C
RPG
RP
RP
CP
Figure 3-24. Interface Functions for MSC with C7
Each RPG can handle four C7 ST.
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GSM 1900
The PCM links of the A-interface (TRC-MSC or TRC/BSC-MSC)
are terminated on ETCs in the BSC and are controlled by RALT
software. Both speech and data channels (each 64 kbps) on the
links are defined as RALT devices. The SS7 signaling link is
provided by an S7-Signaling Terminal (S7-ST).
The incoming data channels on the A-interface from the MSC are
switched in the GS to speech coded channels over the A-bis
interface. The SS7 signaling path is provided by a separate link
interconnecting two S7-STs, one in the TRC/BSC, and one in the
MSC – see Figure 3-25.
MSC
TRC/BSC
Figure 3-25. SS7 MTP Connection
CONNECTION OF RALT
A RALT device is defined as fully connected if Extension Module
(EM), Signaling Network Terminal (SNT), Circuit Identity
Code (CIC), and Destination Point Code (DPC) are connected
and if the device is not in the pre-post Service State. The possible
RALT states are:
• IDLE
•
•
BUSY
•
TEST
•
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GSM BSC Operation
These steps need to be taken for the connection of RALT:
•
•
RP, Connect
•
Switching Network Terminal, Connect
•
EM for RP, Connect
•
Radio X-ceiver Administration, Digital Path, Connect
Initial Data for DIP
C7/SS7 SIGNALING
C7/SS7 is the signaling system selected for GSM. The system is
made up of the MTP and a number of User Parts (UP). An MTP
enhancement introduced Signaling Connection and Control Part
(SCCP) which caters to a number of signaling variations including:
•
•
Connection Oriented (CO) - where the first signal sets up a
connection and all the following signals for the same operation
follow the same path through the network. All signals are sent
and arrive in sequence. CO signals are circuit-related, for
example, setting up a speech connection between the MSC and
the BSC, where the signaling refers to a specific speech circuit
to be used for the call.
ConnectionLess (CL) - where each signal for the same
operation is routed independently through the network. CL
signals are non-circuit related, for example, signaling only
connection between the GMSC and the HLR at interrogation.
MTP is implemented in the TRC/BSC by software and hardware
(signaling terminal). BSSAP is an MTP/SCCP user over the A and
A-ter interface and is implemented in software. MTP is divided
into three layers:
•
•
•
- 98 -
Layer 1 provides a bearer for the signaling link.
Layer 2 checks data and corrects any errors that occurred
during transmission.
Layer 3 establishes, maintains and releases connections and
handles addressing and circuit routing.
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3 BSS Configuration
CONNECTION OF MTP LAYERS 1 and 2
These steps are required to set up layers 1 and 2 in the BSC:
•
•
Definition of RP (RPG)
•
Connection of SNT to GS
•
Definition of EM
•
Activation of connections between devices and GS
Semi-permanent connection
CONNECTION OF MTP LAYER 3
MTP Layer 3 handles signaling message handling and signaling
network management functions.
Signaling Message Handling Functions
These functions ensure that messages originated by a particular
user part in one signaling point (SP) (originating point) are
delivered to the same user part at the destination point. These
functions are based on the routing label contained in the message
data packet. Message handling at each SP consists of:
•
•
•
The discrimination function - which is used at an SP to
determine whether a message is received or not, is destined for
it.
The message distribution function - which is used at each SP
to deliver the received message to the appropriate user part.
The message routing function - which is used at each SP to
determine the outgoing signaling link that the message is to be
sent on.
Signaling Network Management Functions
These functions provide reconfiguration of the network in the event
of network failure and control traffic in case of congestion (Refer
to figure 3-26). They are divided into:
•
LZT 123 3801 R7A
Signaling traffic management - which communicates with
other SPs and also STPs to inform them, for example, that a
change in the routing of a message has occurred due to a faulty
signaling link.
© 2006 Ericsson
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GSM BSC Operation
•
•
Signaling link management - which controls locally
connected link sets and interacts with the signaling link
functions of Level 2.
Signaling route management - implements rerouting of
messages.
Figure 3-26. Signaling Network Functions
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3 BSS Configuration
BSSAP
BSSAP is a protocol that has been developed for the signaling over
the A and A-ter interface. The device used for BSSAP signaling
must be a semi-permanent connection through the TRC, or
BSC/TRC to the BSC. It utilizes MTP and SCCP. BSSAP supports
messages sent between the MSC and the BSC/BTS, that is,
messages sent over the A-interface. In addition, it supports
messages sent transparently between the MSC and the MS in
Figure 3-27.
Figure 3-27. BSSAP Structure
BSSAP consists of three parts:
•
•
•
LZT 123 3801 R7A
Base Station System Management Application Part
(BSSMAP) - which consists of signals such as cipher mode
command, cipher mode complete, and paging. These signals are
MS related and are sent between the MSC and the BSC.
Direct Transfer Application Part (DTAP) - which consists of
signals such as authentication request and reject, and location
updating accept and reject. These signals are associated with a
specific MS in connection oriented mode. The messages are
sent transparently through the BSC/BTS.
Distribution function - which
BSSMAP and DTAP messages.
discriminates
© 2006 Ericsson
between
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GSM BSC Operation
Initial MS Messages
There are some messages that are meant to be sent transparently
between the MSC and the MS, but to which the BSC adds some
information. These messages are called Initial Address Messages:
•
•
Location Updating Request
•
IMSI Detach
•
Paging Response
CM Service Request
When the BSC receives an initial MS message, the BSC analyzes
parts of the message, adds the CGI and sends it to the MSC in a
message called Complete Layer 3 Information. The CGI can, for
example, be used for charging (home cells) and for routing
emergency calls to the nearest emergency center.
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A-BIS INTERFACE
An ETC is used at the TRC/BSC or BSC for the A-bis interface
with the RBS. The ETC is controlled by RBLT software and
terminates a digital link (either E1 or T1).
The 64 kbps channels on the digital link are defined in software as
RBLT devices. One such device is used to provide a signaling
control path to the RBS 200 for control of the TRI. In addition,
RBLT devices provide speech and data call paths and LAPD
signaling paths for control of the transceivers.
The AXE control signaling path to:
• RBS 200 is over one 64 kbps channel terminated by an STC
Function in the form of a RPG and an STR in the RBS - see
Figure 3-28.
•
RBS 2000 is integrated with the LAPD signaling path.
To support LAPD signaling, TRH devices are required. To support
speech, TRAU devices are required.
RBLT
RPG
GS
RBLT
TRAU
TRH
RPG
RP
RP
RP
SP
CP
Figure 3-28. BSC - RBS 2000/200 Interface Functions
CONNECTION OF RBLT
The functional block ABIS is part of the Radio Transmission ans
Transport Subsystem (RTS) in APT and has the following
features:
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GSM BSC Operation
•
•
Provides and administers data for RBLT devices.
Is fully connected if the EM and SNT are connected and if the
device is not in pre-post Service.
The devices have these states:
– IDLE
– BLOC
– TEST
– SEBU
Note the following for the connection and disconnection of radio
equipment in the BTS:
•
•
•
•
When connection is in progress, RBLT devices interfacing to
TRAUs and TRHs in the BSC are allocated by the Transceiver
Administration Subsystem (TAS) before they are seized.
When disconnection occurs, the allocation is released.
Allocation and allocation release are initiated by command.
The state of the device must be blocked or idle at allocation and
the function allocation prevents a fault state when RBLT
devices are seized later.
LAPD SIGNALING
All messages sent on the A-bis interface use LAPD protocol
enabling safe transmission of information. LAPD provides two
types of signals:
•
•
Acknowledged (the most common).
Unacknowledged (used for measurement reports only).
LAPD links are provided for:
•
•
•
- 104 -
Radio Signaling Link (RSL) - which serves Traffic
Management Procedures of Level 3.
Operation and Maintenance Link (OML) - which serves
Network Management Procedures of Level 3 (used for BTS
O&M messages).
Layer 2 Management Link (L2ML) - which serves the Level
2 Management Procedures and is used for the management of
data links sharing a physical connection.
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C/R = Command/Response
EA = Extended Address
FCS = Frame Check Sum
Info = Layer 3 information, RSL or OML messages, max. 249 octets plus
an LAPD header
N(R) = Receive sequence number
N(S) = Send sequence number
P/F = Poll / Final bit
SAPI = Service Access Point Identifier
TEI = Terminal Endpoint Identifier
Figure 3-29. Illustrates the LAPD frame structure.
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GSM BSC Operation
Figure 3-30. Logical Configurations of the A-bis Interface for the RBS
200
TRUs in the RBS 2000, and TRXs in the RBS 200 are referred to
as terminal equipment. Each data link is identified by a TEI/SAPI
pair, unique for each physical connection. Each physical
connection can support a number of data links. See Figure 3-30.
•
•
Terminal Endpoint Identifier (TEI) - signaling links over the
A-bis interface are addressed to different physical entities by
TEI.
Service Access Point Identifier (SAPI) - different functional
entities within one physical entity are addressed by SAPI.
LAPD Link Provision is an automatic function reconfiguring
LAPD signaling links in the event of failure of some links due to
problems in the TRH.
In the event of an error in a TRH, all connections handled by the
faulty TRH and links provided on them, are reallocated to other
TRH equipment, if available. Logical channels existing on those
links remain after reallocation.
The utilization of time slots on the PCM links between the BSC
and the RBS is illustrated in
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Unconcentrated
0
1
2
3
4
5
6
7
8
9
10
11
12
24
31
24
31
syn sig s-d s-d sig s-d s-d sig s-d s-d sig s-d s-d
Concentrated
0
1
2
3
4
5
6
7
8
9
10
11
12
syn sig s-d s-d s-d s-d s-d s-d s-d s-d
Figure 3-31. PCM towards the RBS 2000
Signalling Layer 3
Connection Management
CC
MSC
BSC
SS
SMS
Mobility Management
MM
Radio Resource Management
RR
Sinalling Layer 2
BCCH PCH RACH
SACCH
AGCH
SDCCH
FACCH
Cell
Broadcast
Functions
CBCH
TCH
Sinalling Layer 1
Figure 3-32. Radio Interface Signaling Layer 3
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GSM BSC Operation
RADIO INTERFACE (UM) SIGNALING LAYER 3
Layer 3 takes care of the signaling procedures between the mobile
station and the network. See Figure 3-32. It has been divided into
three sub-layers:
•
•
•
•
Radio Resource management (RR)
Mobility Management (MM)
Connection Management (CM)
Radio Resource Management (RR)
The RR sub-layer consists of functions required establishing,
maintaining and releasing the RR connection on dedicated control
channels. Functions performed by the RR sub-layer include:
•
•
•
•
Cipher mode setting
Change of dedicated channel while still in the same cell, for
example, from an SDCCH to a TCH
Handover from one cell to another
Frequency re-definition (used for frequency hopping)
The RR messages reside in the BSC on the network side. They are
sent transparently through the BTS.
MOBILITY MANAGEMENT (MM)
The MM sub-layer contains functions related to the mobility of the
mobile subscriber:
•
•
Authentication
•
Identification of the MS, by requesting IMSI or IMEI
•
TMSI reallocation
•
Location registration
IMSI detach and attach
IMSI detach may be performed by the MS to indicate that it is not
reachable, so that incoming calls can be forwarded or blocked by
the network without paging the MS. Messages to and from the CM
layer are transferred transparently by MM. CM on the transmitting
side requests the establishment of an MM connection, and MM
requests, in turn, the establishment of an RR connection.
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CONNECTION MANAGEMENT (CM)
The CM sub-layer consists of three entities:
•
•
•
LZT 123 3801 R7A
Call Control (CC) - which provides functions and procedures
for ISUP call control, although, modified for adaptation to the
radio environment. It also provides call re-establishment and incall modification of bearer services during a call, for example,
changing from speech to data is a specific procedures included
in CC. CC also contains functions for call specific
supplementary services such as user-to-user signaling.
The Supplementary Services (SS) support handles
supplementary services not related to a specific call, such as,
call forwarding on no reply and call waiting.
The Short Message Service (SMS) support entity provides the
higher-layer protocols for short message transfer between the
network and a specific MS.
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GSM BSC Operation
A-TER INTERFACE
The interface between the TRC and BSC (or BSC/TRC and BSC)
is the A-ter interface. The PCM links of the A-ter interface are
terminated on ETCs. In the BSC they are controlled by RTLTB
software, and in the TRC (or BSC/TRC to BSC) they are controlled
by RTLTT software.
BSC/TRC Application Part (BTAP) is the proprietary protocol
used for signaling between the BSC and the TRC.
When a BSC/TRC physical node is in use, the Ater interface
signaling is internally transferred between the logical nodes BSC
and TRC and vice versa.
Signaling system No.7 is used for the exchange of signaling
information between the BSC and the TRC. The signaling
connection control part (SCCP) of signaling system No.7 provides
the possibility to carry information between the BSC and the TRC.
The SCCP provides two different signaling principles,
ConnectionLess (CL) and Connection Oriented (CO) signaling.
When a number of associated messages are sent, a logical signaling
connection can be established and CO messages can be sent on the
signaling connection. The BSC/TRC Application Part (BTAP)
sends messages associated with mobile traffic in the CO mode, and
all other messages are sent in CL mode. No signaling occurs
directly between the MSC and the TRC.
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ETC 155 MBIT/S
INTRODUCTION
The ETC 155 hardware can be used to connect different switches to
the SDH transport network - see Figure 3-33. The interface can be
optical fibers or electrical cables.
STM – 1
Drop
BSC
Group
Switch
ETC 155
ETC 155
SDH Ring
MSC
DL3
STM – 1
Optical
Or Eletrical
STM:Synchronous Transfer Mode
Figure 3-33. ETC 155 Enables Connection to SDH
DESCRIPTION
The SDH (Synchronous Digital Hierarchy) standard was originally
introduced in the now called transport networks. I.e. the BSC can
be connected via SDH to the MSC.
ETC 155 is an SDH interface, supporting both electrical (155.52
MHz) and optical (1310 nm) communication. The ET155
terminates an STM1 (Synchronous Transfer Mode) and contains 63
E1/T1. The ETC 155 is not a part of the SDH network but is
connected to the SDH network.
The ETC 155 introduces several advantages, namely:
•
•
•
•
LZT 123 3801 R7A
Simplicity - the node is directly connected to the transport
network;
Greater functionality;
Reduction in hardware - sixty-three 2 Mbit/s ETC cards in 4
GDM have been replaced by a single ETC 155.
Simplified network management - the ETC 155 is controlled by
the APZ, while telecommunications management network
(TMN) controls transport network products.
© 2006 Ericsson
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GSM BSC Operation
HARDWARE
BYB 501
420 mm
260
mm
Figure 3-34. Magazine Containing 2 ETC 155-7
The hardware of the ETC 155-7 –see Figure 3-34 and 3-35 consists
of the following products:
•
•
•
•
- 112 -
The High Order Termination Unit (HOT) will handle the
termination of the higher order layers of SDH. There are two
HOT versions: with optical S-1.1 inter-face and with electrical
CMI interface.
The Low Order Termination Unit (LOT) will terminate the
lower order layers of SDH as well as the termination of PDH.
The LOT also terminates the group switch network (DL3).
The magazine (420 x 300 x 300 mm) includes two protected
ETC 155. Controlling RP pairs are included in the same
magazine.
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HOT protection
LOT working
LOT protection
EMC shield
HOT working
RP 4
Same as left side
Figure 3-35. Boards of ETC 155
Protection
For reliability reasons, it is possible to have protected equipment
and/or a protected network transmission path.
An equipment protection function is provided by adding a 5th LOT
card, with an additional DL3 interface.
The network protection function provides protection against loss of
traffic on the STM-1 link. Adding a 2nd HOT card and a 2nd
transmission link provides this. MSP1+1 (Multiplex Section
Protection) is used, permanently bridged, non-revertive switching.
The STM-1 interface is thereby duplicated, with one active and one
protecting STM-1 link. Permanently bridged means that the same
traffic is transmitted on both STM-1 interfaces. Non-revertive
switching means that there will be no switchback if the
defect/degradation of the STM-1 signal ceases.
Therefore a change of a LOT or a HOT board is possible without
interrupting the traffic. The procedure to replace a card in a
magazine with protection is described in OPI: Switching Network
Terminal with SUBSNTS, Repair.
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GSM BSC Operation
Integration in AXE
ETC 155 HW definition in AXE follows the same principles as for
conventional ETC connection. But to comply with the increased
complexity a new concept for SNT and DIP is introduced.
In addition to the SNT there exist subordinate SNTs (SUBSNT).
In addition to the normal DIPs there exist a high level DIP for the
SDH (SDIP).
Mix of ETC in the Same BSC
This feature makes it possible to mix different broadband ETC
(ETC 155 with 2.0/1.5 ETC. In addition, it makes it possible to mix
E1 (32 channel PCM) with T1 (24 channel PCM) in the same BSC
and on the same interface (A-, Abis-, Ater- and Gb-interface).
The commands for setting transmission type are removed
(RARMC and RARMP).
AXE 810
AXE 810 hardware significantly reduces the size of the ETC155-7
magazine to a single board ETC155-1 as seen in Figure 3-36. The
ETC155-1 board which incorporates an integrated RP (RPI) on the
board is located in the GEM subrack. It connects to the GS890
Group Switch also located in the GEM. The ETC155-1
incorporates exactly the same features as the ETC155-7 such as
protection against hardware failure and against loss of incoming
traffic stream.
420 mm
260
mm
Figure 3-36. AXE 810 ETC155-1 Hardware
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The protection facility utilizes duplication of the ETC155 board
and consequently the corresponding STM1 optical input port. This
is illustrated in Figure 3-37.
ET155-w
X
Working
Protection
ET155-p
DL34
Figure 3-37. Protection Hardware for ETC155
OPERATION
SUBSNT 1
DL3
SNTINL 0-15
DL3
SNTINL 16-31
TSM
(Group
Switch)
DL3
SNTINL 32-47
DL3
SNTINL 48-62
DL3
LOT 1
ET155
Dev 0 - 511
SUBSNT 2
SUBSNT 0
LOT 2
HOT
Dev 512-1023
SUBSNT 3
LOT 3
Dev 1024-1535
SUBSNT 4
LOT 4
Dev 1536-2015
SUBSNT 5
SUBSNT 6
HOT
Protection
SDH
155 Mbit/s
(MSP1+1)
LOT
Protection
Figure 3-38.
Schematic Allocation of SNT, SUBSNT, SNTINL and
Device Numbers in an ETC 155
An RP pair is controlling 7EM in an ETC 155 subrack and EM 0 &
6 are HOT and EM 1 through 5 are LOT.
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GSM BSC Operation
The ETC 155 is regarded as Switching Network Terminal (SNT).
As usual NTCOI initiates the connection of a Switching Network
Terminal (SNT) to the group switch. LOT and HOT for one STM-1
termination are regarded as one SNT. Each LOT or HOT is a
subordinate SNT (SUBSNT). The SNT consists of a maximum of
seven SUBSNTs .
A Parameter EQLEV (Equipment Level) indicates the number of
LOTs used. The Parameter PROT indicates whether and how the
protection level is used, where 0 = no protection, 1 = LOT
protection, 2 = HOT protection and 3 = both LOT and HOT
protection..
Several device types can be connected to the same ET155 SNT.
Therefore, when devices are connected, the SNT unit and the SNT
inlet must be specified. An SNT inlet (parameter SNTINL) is equal to
a 2 Mbit/s connection within one ET155. Example:
RALT devices are connected to the SNT inlets in the ET155. For
the first ET 155 in a magazine, SNT unit 0 is used and for the
second SNT unit 1.
EXDUI : SNT=ET155-0, DEV=RALT-0&&-31, SNTINL=0;
EXDUI : SNT=ET155-0, DEV= RALT-32&&-63, SNTINL=1;
until
EXDUI : SNT=ET155-0, DEV= RALT -1984&&-2015,
SNTINL=62;
A new NTDCP command exists to perform a printout of
dynamically connected devices. The existing NTSTP printout is
adapted:
NTDCP : SNT= ET155-3, SUBSNT=2;
NTSTP : SNT= ET155-3;
Insertion of DIP has to follow a new concept. For one ET155 first a
Synchronous Digital Path (SDIP) is defined:
TPCOI:SDIP=0ET155, SNT=ET155-0;
Then to all 2 Mbit/s links a “normal” DIP is assigned:
DTDII:SNT=ET155-0, DIP=RALT0, DIPP=0;
DTDII:SNT=ET155-0, DIP=RALT1, DIPP=1;
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3 BSS Configuration
until
DTDII:SNT=ET155-0, DIP=RALT62, DIPP=62;
Operational Instruction
Switching Network Terminal With SUBSNTs, Repair
Synchronous Digital Path Fault Supervision
Synchronous Digital Path, Blocking
Synchronous Digital Path, Connect
Synchronous Digital Path, Connection, Change
Synchronous Digital Path, Disconnect
Synchronous Digital Path, Fault Supervision Severity
Synchronous Digital Path, Initial Data, Change
Synchronous Digital Path, Trail Trace Identifier Mismatch
Detection, End
Identifier Mismatch Detection, Initiate
Synchronous Digital Path, Trail Trace Identifier, Change
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GSM BSC Operation
BSS ARCHITECTURE FOR GPRS
GPRS and circuit switched GSM can co-exist within existing GSM
infrastructure, enabling wide coverage of GPRS to be implemented
easily in pre-existing GSM networks. GPRS requires specific
software in BSS and the Packet Control Unit (PCU) hardware
located with the BSC node – see Figure 3-39. The BSC may be a
combined BSC/TRC or a stand-alone BSC. The PCU can only
serve one BSC and there will only be one PCU per BSC. The Gb
interface, is an open interface between the PCU (BSC) and SGSN.
The existing A-bis interface is used for GPRS and carries both
circuit switched (CS) and packet switched (PS) traffic.
CCU
BTS
Std.
Abis
BSC
Gb
SGSN
PCU
CCU
PCU = Packet Control Unit (Hardware and Software)
CCU = Channel Control Unit (Software)
Figure 3-39. GPRS Impact in the BSC
BSC AND PACKET CONTROL UNIT
The PCU is responsible for the GPRS packet data radio resource
management in BSS. In particular, the PCU is responsible for
handling the Medium Access Control (MAC) and Radio Link
Control (RLC) layers of the radio interface, and the BSSGP and
Network Service layers of the Gb interface. The Gb interface is
terminated in the PCU.
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The PCU consists of both central software (CP) and hardware
devices with regional software (RP). It has one or more Regional
Processors (RPP), up to a maximum number of 64. An RPP can
work towards both the Gb and the A-bis interface, or towards A-bis
only. The function of the RPP is to distribute PCU frames between
Gb and A-bis. Where there is just one RPP in the PCU it will work
towards both Gb and A-bis interfaces. Where there is more than
one RPP, each RPP may work towards either A-bis or towards both
Gb and A-bis. Where more than one RPP is used (except for the
two RPPs in an active/standby configuration) they will
communicate with each other by means of Ethernet. A duplicated
Ethernet connection is provided in the backplane of the PCU
magazine. In addition, some HUB boards are needed to connect the
RPPs via the Ethernet. The HUB boards are doubled for
redundancy reasons.
A cell cannot be split between two RPPs. If an RPP does not handle
the cell that a message is destined for, the message is forwarded via
the Ethernet connection to the RPP which is handling the
destination cell.
The PCU connects to the Gb devices via the group switch (GS),
and to the A-bis devices via the GS and the subrate switch (SRS) as
shown in Figure 3-39. The RPPs are connected to the group switch
via DL2s and to the central processor CP via the RP bus. The
GPRS traffic is multiplexed with the circuit switched traffic in the
subrate switch.
The “PCU” has a maximum of 64 x 150 16kbps = 9000 or 64 x
56kbps = 3584 packet data channels.
This means there are maximum 18 16 kb/ cell or 764 kb/cell of
packet data timeslots in a BSC.
The Gb interface has a maximum capacity of 64 x 2048 kbps.
GS
PCU
Gb
Abis
RPP
GSL
RPP
GSL
GSL
ETC
Gb interface
(From SGSN)
ETC
Ater (From TRC)
used for CS only
ETC
BTS
SRS
LZT 123 3801 R7A
PCU - Packet Control Unit
GSL - GPRS Signaling Link
ETC - Exchange Terminal Circuit
SRS - Sub Rate Switch
© 2006 Ericsson
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GSM BSC Operation
Figure 3-40. PCU/SRS Interworking Block Diagram
The PCU architecture is scalable to achieve cost effective solutions
for both small and large PCUs. In order to enable capacity
expansions several magazines containing RPPs and HUB boards
can be connected. For more information about the actual capacity
of the PCU and the RPP, refer to the PCU description, and the PCU
dimensioning guide.
PCU SYSTEM FEATURES
A number of system features relating to PCU operation have been
introduced in R10 to improve the GPRS/EGPRS performance.
These features include the following:
•
•
•
Detect and release hanging PDCHs and TBFs in PCU
Gb Link Recovery
Load regulation of CS paging via PCU
Detect and Release Hanging PDCHs and TBFs in PCU
A hanging TBF is detected if a TBF is occupied without any
ongoing activity for a specified time period (a 5 minute timer is
started at TBF-start). In this case, the PDCHs involved remain in
Busy state and are not returned to CS traffic. Hanging TBF is
released by the existing Forlopp auto-release mechanism. The
feature ensures that more PDCHs are available for multislot users
and more PDCHs are returned to the CS domain.
Gb Link Recovery
Gb link recovery ensures that a lost Gb link is recovered
immediately and while the Gb link is unavailable an attempt is
made to restore new Gb links. This is achieved by finding a
suitable alternative range of GPH devices and avoids any reduction
in Gb bandwidth for a long period of time.
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Load Regulation of CS paging via PCU
Load regulation of paging on the Gb interface controls the CS
paging handled via the PCU and consequently protects the CP from
overload in situations of excessive paging load. CS paging is load
regulated in the TRH for paging response messages handled on the
A-Interface. This includes responses to page messages sent to the
MS on the Gb interface via the PCU. In this case the CHANNEL
REQUIRED response is returned via TRH, which prior to R10 was
only load regulated for CS traffic. While GPRS traffic remains
below 5-10%, this does not cause problems. When PS traffic
increases above this level, load regulation in the PCU is required to
protect the CP from Complete Exchange Failure (CEF) caused by
CS paging overload.
BTS AND GPRS
GPRS functionality is implemented in the BTS software and no
new BTS hardware is required. GPRS is supported on both RBS
2000 and RBS 200 platforms. The RBS 200 platform must be
equipped with SPU++ or ‘SPU+ with SPE’ as SPP does not support
GPRS. In the initial GPRS implementation, coding schemes CS-1
and CS-2 only were supported. In the R9.1 BSS release, CS3 &
CS4 as well as the Coding Schemes used by EDGE were
introduced. All RBS types support the GMSK Coding Schemes i.e.
CS1, CS2, CS3 & CS4 with the exception of RBS 2301 without a
DSP cluster which supports only CS-1. Only RBS 2206 is capable
of supporting GMSK as well as the 8PSK coding schemes used in
EDGE.
Note: If the operator has set the preferred channel coding scheme
the BSC will switch to CS-1 in the cell with RBS2301 as above in
case the BTS is not capable of CS-2.
ABIS INTERFACE
The existing transmission and signaling links over the Abis
interface are used for GPRS and modified TRAU frames are used
for the support of GPRS Coding Schemes. No additional
transmission links are needed (unless, of course, the number of
TRXs per site is increased).
GB INTERFACE
The Gb interface is an open interface between the PCU and the
SGSN. The PCU can be connected to an SGSN over the Gb
interface using one of these methods:
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GSM BSC Operation
1. Directly from a stand-alone BSC or a combined BSC/TRC.
2. Via a TRC from a stand-alone BSC.
3. Via an MSC from a stand-alone BSC or combined BSC/TRC.
A BSC can use one or more physical links to connect to an SGSN.
When using an E1 interface the size of the physical links is
between 1 and 31 64Kbits/s time slots, that is, between 64 kbits/s
and 1984 kbits/s.
When using a T1 interface the size of these physical links is
between 1 and 24 64Kbits/s time slots,that is, between 64 kbits/s
and 1536 kbits/s.
Note: If more than one 64kbits/s circuit is used on the same
physical link the time slots must be contiguous with each other.
Gb protocols
The protocol used to provide layer 3 is BSSGP which is a GPRS
specific protocol. It conveys the necessary routing information to
make it possible to transfer an LLC PDU transparently across the
radio network to the MS. Layer 2, the Network Service (NS) layer
is further divided into two separate layers. The upper layer is the
Network Service Control and the lower layer is the Sub-Network
Service.
The protocol used to provide the Network Service Control layer is
the Network Service Control protocol. The Network Service
Control protocol provides a generic way of encapsulating BSSGP
PDU and transferring them via the Sub-Network Service.
The protocol used to provide the Sub-Network Service layer is
Frame Relay. Frame Relay is a frame mode interface specification
providing a signaling and data transfer mechanism between endpoints and the network. The end-points of the Gb interface are the
BSC and the SGSN. Frame relay should transparently transfer NS
PDUs between an SGSN and a BSC.
Addressing and Configuration of the Gb Interface
An SGSN can interface to several BSCs, however one BSC can
only interface to one SGSN. BSC can interface to SGSN via an
intermediate transmission network (a Frame Relay network), or via
point-to-point connection(s). A BSC can use one or more physical
links to connect to an SGSN.
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Flush
When an MS in packet transfer state moves to another cell it sends
a cell update to the SGSN. The SGSN then sends a flush message
with mobile identity and cell identity for the old and the new cell to
the PCU. If both cells are handled by the same PCU and the PCU
has a queue of packets for that MS, these packets are moved to a
queue for the new cell. If the new cell is handled by another PCU,
the packets directed to the old cell are deleted and higher layers
will handle the retransmissions.
Network Assisted Cell Change
The Network Assisted Cell Change (NACC) introduced at R10
reduces the service outage time for a NACC GPRS/EGPRS MS in
packet transfer mode performing an intra-BSC cell reselection. The
service outage time is reduced to less than 0.3 seconds as the GSM
RAN network assists the MS before, during and after the cell
change by sending the minimum required system information about
the new cell to the MS. This occurs when the MS indicates it is
going to make a cell reselection during packet transfer mode, so
that the TBF can be established in the new cell immediately. After
TBF establishment in the new cell, the GSM RAN sends the
remaining set of system information.
When a cell reselection does take place, it is also detected faster by
the SGSN as the cell update is sent immediately in the new cell.
This allows the TBF to be released earlier in the old cell and better
utilizes available resources. In order to avoid unnecessary
retransmissions in the new cell, the GSM RAN also attempts to
finish the transfer of the current data packet (LLC PDU) by
delaying the cell change, allowing the GSM RAN to time the cell
change to coincide with the completion of the current LLC PDU.
As retransmissions are avoided, the effects of cell change on higher
layers are minimized as well as the impact to the end-user service.
Services with high demands on throughput and delay can be
utilized more effectively in situations where the user is moving
quickly through the network (e.g. in trains).
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GSM BSC Operation
NEW FEATURE
A-BIS OVER IP
With the Abis over IP feature operators can use IP based transport
network to connect RBSs to the BSC, and in that way benefit from
potentially lower pricing of IP based transport services.
With the introduction of IP as transport mechanism for Abis, packet
transport is introduced. That offers flexibility to allocate resources
on demand and to use IP based transport services. IP over Ethernet
is used as interface for Abis to the RBS and the BSC, thereby
opening up for connection to almost any IP based transport
equipment. The feature also opens up for transport sharing with
WCDMA and integrated RBS site transport.
With the introduction of IP as transport mechanism for Abis, packet
transport is introduced. That offers flexibility to allocate resources
on demand and to use IP based transport services. IP over Ethernet
is used as interface for Abis to the RBS and the BSC, thereby
opening up for connection to almost any IP based transport
equipment. The feature also opens up for transport sharing with
WCDMA and integrated RBS site transport.
Technical Description
This feature introduces support for usage of IP based transport
networks as an alternative to the E1/1 based leased lines. Abis over
IP does not by itself give significantly lower bitrate than traditional
circuit base transport, but can be combined with Abis Optimization
to support IP over narrow links.
SW
BSC
SW & HW
RBS
GS
EI
GPH
Ethernet
backplane
IP/Network
PGW
TRA
BSC Lan Switch
TRH
IP
Network
er
th
/E
IP
t
ne
PSTU
TRO
IXU
TRO
Synchronisation server
Figure 3-41. A-bis over IP
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The IP termination is done on a packet gateway board (PGW) in
the
BSC and on the Packet Switched Termination Unit (PSTU) in the
RBS. There is one PSTU per TG. Support in the DXU/IXU and
TRU is also required. IPv4 and L2TP are used. The interface to the
BSC and the RBS is IP on Ethernet. The IP addresses of the PSTU,
the time server and the L2TP control protocol in the PGW are
configured in the PSTU. The PSTU also has to be configured with
IP parameters, ID and IP address of the O&M system (OSS).
The PGW has its own IP address configured and a list mapping
PSTU identities to transceiver groups. When the PSTU is fully
configured and ready to handle traffic, the PSTU initiates
communication with the PGW. Traffic channels are bundled into
common IP packages in order to keep the overhead down, thus
reducing the bitrate. As bundling introduces a delay, it is possible
to configure the maximum packet size and maximum waiting time
(before sending a packet), thereby making this delay configurable.
DiffServ can be used to give traffic types different priority.
Traffic with the same priority is bundled into common IP packets in
order to keep the IP overhead to a minimum. DiffServ values are
configurable for each traffic type per Abis link. The traffic types
are RSL (signaling), OML (O&M), Speech, CS data and
GPRS/EGPRS.
The PGW is one or more devices in the BSC. The PGW handles
speech, GPRS/EGPRS and signaling. The number of boards
depends on the number of connected TRXs and the traffic mix. The
same PGW can be used both for optimized Abis and Abis over IP.
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GSM BSC Operation
The same BSC LAN Switch and the IP Connectivity feature as
used for other IP based interfaces in the BSC (e.g. Gb/IP) are used
also for Abis over IP. RBSs connected via IP and RBSs connected
via E1s/T1s can be mixed in a BSC. The PSTUs are managed as
stand alone network elements. The O&M support is implemented
in OSS. O&M for BSC, BTS and LAN switches is handled as in
previous releases. RBSs connected via IP cannot derive synch from
the TDM network, and hence need another source of
synchronization. This can be achieved using a local synch source,
e.g. GPS, or by distributing synchronization information over the
IP network. If synchronization distribution over the IP network is
used a synchronization server have to be used. NTP is used to
distribute synchronization information and a function to recreate
clock is implemented on the PSTU board. The number of
synchronization servers needed in a network and their placement
depends on the number of RBSs and the characteristics of the IP
network. It is assumed that transport service over the IP network is
secure. If the transmission is performed over an open IP network
external security solutions must be used.
NETWORK IMPACT
BSC HW Impact A new board (PGW) is required in the BSC. The
AXE 810 group switch is required. NNRP4/NNRP5 can be used
for expansion of BYB501/AXE10. The BSC LAN switch is
required. If multiple GEM magazines are needed for PGWs and
more than one of these GEM magazines result in traffic above 100
Mbit/s, a Gigabit
Ethernet Switch Board (GESB) is also required to connect the
multiple magazines. Support for the feature is first introduced in
RBS 2308/2109/2309. A packet termination unit (PSTU) is
required in the RBS.
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MANAGED OBJECTS (MO)
An MO is a logical representation of hardware units and software
in the BTS. However, hardware units may actually be shared
between MOs of different classes. These classes include:
• Transceiver Group (TG)
• Central Function (CF)
The CF is the control part of a TG. It is a software function,
handling common control functions within a TG. There is one CF
defined per TG.
• Digital Path (DP)
Digital Path Layer 1 reception and transmission are not part of the
BTS logical model. However, each of the PCM systems
terminating in the TG has an associated managed object known as
the DP. Reports of transmission faults and supervision of
transmission quality are carried over the A-bis O&M interface.
That signaling is described using the DP. There can be up to four
DPs defined per TG.
• Concentrator (CON)
The CON (also known as the LAPD Concentrator) is used by the
optional feature LAPD Concentration for RBS 2000. Therefore, the
CON, as an MO, is itself optional. There is one CON defined per
TG.
• Transceiver Controller (TRX)
The TRXC controls all the functions for signal processing, radio
reception, and radio transmission. In a normal configuration, each
TRXC (also known as TRX) corresponds to one TRU. There can
be up to 16 TRXCs defined per TG.
• Transmitter (TX) and Receiver (RX)
The MO representing the transmitter functions – for example,
transmitted power and frequency on the bursts sent – is called the
TX. The RX represents the radio receiving functions. There can be
up to 16 TXs and RXs defined per TRXC.
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GSM BSC Operation
• Interface Switch (IS)
The IS provides a system interface to the PCM links and crossconnects individual timeslots to specific transceivers. There is one
IS defined per TG
• Timing Function (TF)
The TF extracts synchronization information from the PCM links
and generates a timing reference for the RBS. There is one TF
defined per TG.
• Time Slots (TS).
TS is the MO that represents the handling of timeslots. There can
be up to eight TSs defined per TRXC.
The TG is a part of the Transceiver Subsystem (TAS). TG
hardware architecture is created to meet an implementation of
baseband or synthesized frequency hopping and demands for
various aerial combining techniques. One TG is normally
synonymous with one BTS. However, in certain applications, more
than one cell can be connected to the same TG, thus sharing
functions in the TG. The TF is always common to all BTSs in the
same TG.
A transceiver is a part of one TG since a TG handles the functions,
common to a number of transceivers. For each cell carrier there
must be a transceiver. The transceiver contains most of the
equipment required to transmit and receive on the carrier.
Communication between a transceiver and the BSC is provided
through the Distribution Switch Unit (DXU).
A BSC can handle the following:
•
- 128 -
•
512 internal and external cells
•
16 channel groups per cell
•
8160 traffic channels
•
256 TRHs
•
2 subcells per cell
•
512 TGs
•
128 frequencies per cell
1,020 transceivers
© Ericsson 2006
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3 BSS Configuration
One TG consists of up to 16 transceivers and can be connected to a
maximum of 16 cells. One channel group can handle 16
frequencies. A cell can be connected to one TG only. Logical
Managed Object (LMO) of the type Logical Time Slot (LTS),
Logical Receiver (LRX), and Logical Transmitter (LTX) have
been introduced as part of the introduction for the support of
frequency hopping. Each Basic Physical Channel (BPC) is
connected to one LTS, one LRX, and one LTX, each of which may
in turn be connected to one or more physical BTS MOs.
The LMO concept is also used to distinguish between the O&M
state of an MO, that is, whether TAS considers an object
operational or not, and its ability to carry traffic, for example,
whether the transmission path to the MO is functioning. Thus, in
maintenance terms, TAS still sees an object as operational if TAS
can communicate through the signaling link even when the
speech/data link has been reported as faulty, disabling it from
carrying traffic.
Additionally, the TF has an associated Logical TF (LTF). This is
due to the requirement that a TF must be synchronized before any
of the time slots are capable of carrying traffic. MOs in the BTS
cannot be configured until synchronization has been achieved. The
command used to print the status of an MO is RXMSP.
Figure 3-42. Managed Object Block Diagram, G12
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GSM BSC Operation
MANAGED OBJECT STATES
Block
RXBLI
NOOP
(SUBORD)
Define/Change
RXMOI/C
UNDEF
Into service
RXESI
Deblock
RXBLE
(SUBORD)
(SUBORD)
COM
DEF
Delete
RXMOE
Out of
service
RXESE
PREOP
Block
RXBLI
MO is defined and in Pre-Post Service state
MO has been taken out of Pre-Post service state
MO is being brought into operation
MO is operational
MO is temporarily not operational
MO is permanently blocked because of faults
OPER
Automatic
(SUBORD)
(SUBORD)
DEF
COM
PREOP
OPER
NOOP
FAIL
Automatic
Automatic
Automatic
FAIL
Block
RXBLI
(SUBORD)
Figure 3-43. Managed Object States
There is a defined order in which all objects are to be defined and
put into operation see fig 3-43.
The parameter SUBORD allows us to take an MO and its
dependency MO from one to another state such as: in and out of
service and from blocked to deblocked state or vice versa.
The three levels are TG, CF and TRX where TG is everything, CF
is everything apart from TG and TRX is TRX, TX, RX and TS.
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CONNECTION OF TG, MODEL G12
The TG hardware architecture is designed to meet implementation
of frequency hopping and demands for various antenna combining
techniques. One cell can be connected to one TG only. One TG is
generally connected to one cell. However, in certain applications,
more than one cell can be connected to the same TG which thus
share the functions in that TG. The TF is always connected to all
BTSs in the same TG. For each pair of radio carrier frequencies
(up-link and down-link) making up a radio channel allocated to a
cell, there must be a TRU in the TG. The TRU contains most of the
equipment needed to transmit and receive on a radio channel.
Communication between TRU and the BSC is through GS. A TG
handles functions common to a number of TRUs (TG can form up
to 16 TRX functions).
A TG consists of:
•
•
•
•
•
•
•
•
•
Central Function (CF)
Interface Switch (IS)
Concentrator (CON)
Timing Function (TF)
Digital Path (DP)
Transceiver Controllers (TRXC)
Transmitters (TX)
Receivers (RX)
Time Slots (TS)
Mandatory data for a CON at definition consists of a list of DCPs.
A total of 24 DCPs must be listed (8 concentrated + 16
unconcentrated). No specific order is needed. The function
‘Administration of MOs’ is responsible for handling the definition
of MOs of class CON. The DCPs given in the command are read in
and a check is made to MO Data Handling to see if these DCPs are
idle. If so, they are pre-seized and the CON is then defined. If they
are not idle, the command will fail.
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GSM BSC Operation
The MOs for RBS 2000 are divided into two major classes:
•
•
Service Objects (SO) handle functionality and are the owners
of specific hardware units in the cabinet.
Application Objects (AO) handle functionality only and are
under the administration of the SOs.
Figure 3-44. MOs in the RBS 2000. Note that “99” is an example TG
designation and can be any number between 0 and 512.
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3 BSS Configuration
Define Managed Objects
This table below can be used as a reference when inducting the MO
Definition exercise at the completion of this chapter.
Figure 3-45. G12 Managed Object reference table
The following command-file is just an example and is intended for
training only:
RXMOI:MO=RXOTG-0, COMB=HYB, RSITE=KISTA,
SWVER=G12R10, TRACO=POOL;
RXMOI:MO=RXOCF-0, TEI=62, SIG=CONC;
RBS
DXU
BSC A-bis
RXOCF-98
TEI=62
RXOTG-98
RXOTRX-98-0
TEI=0
RXOTRX-98-1
TEI=1
RXOTRX-98-2
OM T
TEI=2
RXOTRX-98-3
TEI=3
RXOTRX-98-4
TEI=4
RXOTRX-98-5
TEI=5
Figure 3-46. TEI values in the RBS
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GSM BSC Operation
RXMOI:MO=RXOIS-0;
RXMOI:MO=RXOCON-0, DCP=64&&87;
RXMOI:MO=RXOTF-0,TFMODE=SA;
RXMOI:MO=RXODP-0-0, DEV=RXODPI-2;
RXMOI:MO=RXOTRX-0-0, TEI=0, DCP1=128, DCP2=129&130,
SIG=CONC;
Figure 3-47. DCPs for RXOTRX
RXMOI:MO=RXOTX-0-0, BAND=GSM900, MPWR=40;
RXMOI:MO=RXORX-0-0, BAND=GSM900, RXD=AB;
RXMOI:MO=RXOTS-0-0-0&&-7;
Reserve A-bis Path Resources
RXAPI:MO=RXOTG-0, DEV=RBLT-33&&-35, DCP=1&&3;
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3 BSS Configuration
TR
RXOCF
SNT=
ETRBL -3
RXOI
DIP=3RBLT
DCP
DCP
DEV=RBL -96 to RBLT -127
1
-
33 34 35
2
-
3
-
DEV refers to the devices on the DIP
that are being used for the TG.
DCPs 1, 2 and 3 are used
because the devices (DEV) 33,
34 and 35 are the 9th,
10th and 12th DS0s on the E1
DCP refers to the DCPs in the RXOIS to
terminate the devices in the RBS.
Figure 3-48. DCP connection
RXAPI:MO=RXOTG-0, DEV=RBLT-39, DCP=7[, RES64K;
Parameter RES64K is used to reserve Abis TSs required for GPRS
connections utilizing data rates up to 59.2 kbps when CS3/CS4 and
EGPRS utilized.
As a result of this a printout would look this way.
<RXAPP:MO=RXOTG-14;
RADIO X-CEIVER ADMINISTRATION
ABIS PATH STATUS
MO
RXOTG-14
DEV
RBLT-33
RBLT-34
RBLT-35
RBLT-36
RBLT-37
RBLT-38
RBLT-39
END
DCP
1
2
3
4
5
6
7
APUSAGE
UNDEF
UNDEF
UNDEF
UNDEF
UNDEF
UNDEF
UNDEF
APSTATE
IDLE
IDLE
IDLE
IDLE
IDLE
IDLE
IDLE
64K TEI
NO
NO
NO
NO
NO
NO
YES
Bring Managed Objects into Service and Deblock
RXESI:MO=RXOTG-0, SUBORD;
RXBLE:MO=RXOTG-0, SUBORD;
RXTCI: MO= RXOTG-0, CELL=cell, CHGR=chgr;
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GSM BSC Operation
OTHER USEFULL COMMANDS
RXMDP:MOTY=RXOCF;
RXMDP:MOTY=RXOTRX;
RXMSP:MO=RXOTG-x, SUBORD;
RXAPP:MOTY=RXOTG;
RXCDP:MO=TG-x;
RXTCP:MOTY=RXOTG;
RLSTP:CELL=ALL;
RLCRP:CELL=ALL;
RLCRP:CELL=cell name;
RHDEV/CF
RHDEV/TRX
Status of MO
ABIS
Configuration
MO/CELL
CELL Status
Cell resources
specific cell
resources
Some RBS GSM models available for GSM R12
Figure 3-49. RBS 2206
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LZT 123 3801 R7A
3 BSS Configuration
Figure 3-50. RBS 2106
FAN units
ACCU / DCCU
AC/DC Connection Unit
DXU Distribution Switch Unit
PSU Power Supply Unit
Central Control Unit for the RBS
Converts main supply to 24VDC
TMA Control Module
IDM Internal Distribution
Module
Distribution and fusing of 24VDC
DRU Dual Radio Unit
Complete radio unit for 2 GSM
carriers
Up to 6 DRUs per cabinet
TX output power 46/45,5 dBm
(900/1800) in uncombined mode
RXS RX splitter
For TMA minimization and RX
sharing with other RBSs
Figure 3-51. RBS2X16 Units
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GSM BSC Operation
RBS Characteristics
RBS Type Location
max TRUs
CELLs
Dimensions (W/D/H)
Output Power
(dBm)
Band
12
12
6
6
3
1300/940/1614
600/400/1350
1000/710/1618
600/400/1350
45/47
45/47
45/47
45/47
all
all
all
all
2106
2206
2107
2207
Outdoor
Indoor
Outdoor
Indoor
2108
Outdoor
3
3
(with 3 RRU) (with 3 RRU)
Main- 508/102/363
RRU- 365/189/579
42
900
2111
Outdoor
6
3
(with 3 RRU) (with 3 RRU)
Main- 508/102/363
RRU- 420/220/600
43
900/1800
2109
2308
2309
Outdoor
Outdoor
Outdoor
2112
2116
2216
Outdoor
Outdoor
Indoor
3
2
4
2
1
2
1
433/224/610
433/224/610
433/270/610
43/41,5
34
37
all
all
900/1800
2
1
700/550/1100
49/47
all
12
12
3
3
650/800/1300
600/500/900
46
46
900/1800
900/1800
Figure 3-52. RBSs Characteristics
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LZT 123 3801 R7A
3 BSS Configuration
COMBINING TRANSCEIVER GROUPS IN ONE CELL
The objective of the TG synchronization function is to keep TGs
within a TG cluster synchronized –see Figure 3-53. This is done
via an external synchronization bus. The different TGs within the
TG cluster co-operate according to the master and slave logic. One
of the TGs is selected as master and the other TGs in the TG cluster
are configured as slaves.
580 μS
B S T T T T T T
T T T T T T T T
± 10 μS
A
C
TRU
TX / RX
CDU
TMA
TRU
TX / RX
CDU
TMA
TG-0
TG-1
B
TF-0
TF-1
PCM
Figure 3-53. Two RBS 2000 in the Same Cell
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GSM BSC Operation
FLEXIBLE POSITIONING SUPPORT
INTRODUCTION
Flexible Positioning Support allows operators to introduce
commercial location based services as well as to fulfil the
regulatory requirements of some countries to locate subscribers
who are making emergency calls.
The type of service offered to the subscriber and accuracy of the
location position is dependent on the method used. Three different
methods are used to position a mobile station within the GSM
network. These are:
•
•
Cell Global Identity + Timing Advance (CGI+TA) positioning
with a typical accuracy of approximately 550 metres (low
accuracy).
Assisted Global Positioning System (AGPS) positioning with
accuracy typically better than 10 metres (high accuracy).
POSITIONING ELEMENTS
The Serving Mobile Positioning Center (SMPC) determines which
positioning method is to be used based on the accuracy requested
and the methods supported by the MS and the GSM system. The
SMPC manages the overall coordination and scheduling of
resources to perform the positioning of the MS. It also makes the
final positioning calculations when the CGI-TA mobile assisted is
used, and provides assistance data to the MS for A-GPS positioning
methods.
Flexible Positioning Support allows the connection of 1 SMPC to
many BSCs which allows lower hardware costs, more efficient use
of capacity and simplified administration.
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3 BSS Configuration
POSITIONING PROCEDURES
The BSS implementation supports all standardized positioning
procedures. These are introduced below.
Mobile Originated Location Request (MO-LR) is initiated by the
MS. MO-LR can either be used by the MS to send a positioning
request or to require assistance data from the network. The location
estimate is either returned to the MS or if the user so requires, the
location estimate will be sent to an LCS Client (Location Client
Services).
Mobile Terminated Location Request (MT-LR) is initiated by an
LCS Client. The location estimate is returned to the LCS Client.
Network Induced Location Request (NI-LR) is initiated by the
network. If the network detects that the MS establishes an
emergency call, it initiates a positioning of the MS. The location
estimate is made available to the emergency center by the network.
Note: NI-LR is only applicable for the North American Market.
The procedure is identical to the MT-LR procedure from a BSS
point of view.
DESCRIPTION OF POSITIONING METHODS
CGI+TA
CGI+TA is mobile assisted, parameters being sent to the SPMC
from the MS via the BSC, which means that the location estimate
is calculated by the network, the Serving Mobile Position Center
(SMPC).
Figure 3-54. CGI+TA Positioning for Omni and Sector Cell
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GSM BSC Operation
The position calculation is based on the co-ordinates of the cell
serving the subscriber, the cell configuration such as the antenna
direction, beam width, cell type, cell size and Timing Advance
(TA) value. The TA value determines the distance from the base
station to the subscriber. Accuracy is dependent on the type and
size of the cell. Figure 3-54 illustrates the accuracy possible when
using CGI-TA measurement techniques. This method is compatible
with all existing GSM mobile stations.
A-GPS
The A-GPS method is mobile based which means that the location
estimate is calculated by the mobile terminal.
The position is calculated from GPS measurements performed by
the mobile terminal and GPS assistance data delivered to the
mobile terminal from the network SMPC. The amount of GPS
assistance data delivered is based on what is required by the mobile
terminal at the time of the request. The accuracy is typically 5-10
meters horizontally. A-GPS also supports vertical positioning with
a typical accuracy of 10-20 meters.
A-GPS requires at least additional DGPS (Differential GPS)
equipment in the SMPC and A-GPS capable GSM mobile
terminals are required. Figure 3-55 illustrates the principles
involved in A-GPS.
MS
BTS 1
BTS 3
BTS 2
Figure 3-55. Assisted Global Positioning (A-GPS) System
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LZT 123 3801 R7A
4 Radio Network
4 Radio Network
Objectives:
Configure the Radio Network and define Cell Data knowing
the main parameters and procedure to execute them.
ƒ Explain the purpose of basic BSC Cell parameters and the effects they
have on the GSM Radio Access Network
ƒ Configure the basic radio network in the BSC using MML commands
and parameters
Figure 4-1. Objectives
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GSM BSC Operation
Intentionally Blank
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© Ericsson 2006
LZT 123 3801 R7A
4 Radio Network
INTRODUCTION
THE CELL
A cell is an area where a Mobile Station (MS) receives a signal
strength that is high enough for setting up and maintaining a radio
connection on a dedicated channel, that is, SDCCH or TCH. The
size of a cell (or the size of the coverage area) is mainly determined
by four parameters:
•
•
•
•
The output power (BSTXPWR) at the antenna of the BTS: the
Effective Radiated Power (ERP)
The minimum received level at the MS (this is MSRXMIN for
MS in “busy” mode)
The minimum received level at the BTS (this is BSRXMIN)
The Timing Advance (TA): the TA is a measure of the
traveling time of the bursts between the MS and the BTS; the
maximum value of TA in a cell is defined by the parameter
MAXTA (MAXimum Timing Advance).
A second cell criterion is the existence of a BCCH. A cell must
have exactly one BCCH because the BCCH carries essential
information which must be known to the MS before call setup.
BTS
RXLEV
BSTXPWR
MSRXMIN
distance to BTS
calls possible no coverage
no call possible
Figure 4-2. Cell Range
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GSM BSC Operation
The previous example presented a cell of circular shape, an omnicell. Generally, the shape of a cell depends on the antenna,
connected to the cell. The antenna can also focus its power on a
certain sector of a circle. This is called a sector-cell. It is up to the
cell planner to select a suitable antenna. The cell shape can also
depend on the geographic conditions. Each sector can have its own
output power assigned. The BCCH frequencies must be different in
all the sectors, 3 illustrates two types of sector-cells:
Figure 4-3. Sector Cells
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© Ericsson 2006
LZT 123 3801 R7A
4 Radio Network
THE CLUSTER
The aim of the cell planning process is to provide maximum
capacity with the least interference. The cell pattern and frequency
plan should be designed not only for the initial network, but also
for gradual growth phases. An initial network must be planned to
adapt successive demands on traffic growth.
To prevent interference between cells, a cell pattern, called a
cluster, is designed. In this cluster, a frequency will be used only
once. The aim of a cluster is to have a large frequency reuse
distance. Ericsson uses three types of clusters:
•
7/21
(21 frequency groups in 7 sites)
•
4/12
(12 frequency groups in 4 sites)
3/9
(9 frequency groups in 3 sites)
B1
2
14
26
.
122
C1
3
15
27
.
123
D1
4
16
28
.
124
•
Freq. group
Ch.
A1
1
13
25
.
121
A2
5
17
29
.
B2
6
18
30
.
C2
7
19
31
.
D2
8
20
32
.
A3
9
21
33
.
B3
10
22
34
.
C3
11
23
35
.
D3
12
24
36
.
Table 4-1. Frequency Groups in a 4/12 - Cluster
These frequency groups are then placed in the cluster, as shown in
Figure.4-4 Groups containing adjacent frequencies, for example,
D1 and A2, or D3 and A1 should not be placed as neighboring
cells.
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GSM BSC Operation
A2
A2
A2
A2
A2
A2
Figure 4-4. 4/12 Cell Pattern
As a general rule, adjacent frequencies should have large
geographical distances separation them. Cells, which are neighbors
geographically, should also have a large frequency separation
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CELL DATA
These sections on cell data and locating describe essential cell
parameters. When defining a cell, use these OPIs:
BSC, Internal Cells, Define
BSC, Internal Cell Data, Change
CELL DEFINITION
RLDEI: CELL=cell, CSYSTYPE=csystype, EXT;
A cell can be defined in the BSC as internal or external. Internal
cells are fully controlled by their own BSC while external cells are
not. However, certain data must be known in order to carry out a
handover from a cell in its own BSC to a cell controlled by another
BSC.
CELL: Cell designation or cell name can comprise a maximum of
seven characters. To use the name of the site plus one more
character for identifying the cell within the site; 1, 2, 3, or A, B, C
is recommended, alternatively, to identify the aerial direction of the
cell in a sector-site.
CSYSTYPE: If the BSC global system type is mixed then
CSYSTYPE must be used to define to which system the cell
belongs, GSM800, GSM900, GSM1800 and GSM1900.
EXT: External cell, the cell belongs to another BSC.
Figure 4-5. External, Internal and Outer Cells
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GSM BSC Operation
DESCRIPTION DATA
RLDEC: CELL=cell, CGI=cgi, BSIC=bsic, BCCHNO=bcchno,
AGBLK=agblk,
MFRMS=mfrms,
BCCHTYPE=bcchtype,
XRANGE=xrange;
Figure 4-6.
MSC and LAI
CGI: Cell global identity. Expressed as MCC-MNC-LAC-CI.
Cell Identity (CI): every cell is assigned a CI. This number is
unique per Location Area (LA) and is part of the Cell Global
Identity (CGI). The CGI uniquely identifies a cell within GSM.
Figure 4-7. CGI and LAI
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The CGI is sent to the idle MSs in system information messages.
The combination MCC-MNC-LAC is also known as the Location
Area Identity (LAI). It is important for the cellular network to
know the location of a mobile, since paging signals are distributed
in one LA only. A record in the MSC/VLR administers a mobile
location by means of the LAI as shown in Figure 4-. When the MS
moves from one LA to another, it sends a location update request
to the MSC/VLR.
BSIC: Base Station Identity Code. It is transmitted on the SCH and
is expressed as:
NCC = National Color Code of PLMN. Numeric 0 - 7.
BCC = Base Station Color code. Numeric 0 - 7.
Figure 4-8. BSIC
Each operator in various countries is assigned one NCC value n to
ensure that the same NCC is not used in adjacent PLMNs. The
purpose of the BSIC is to distinguish between cells with the same
carrier frequency but from different clusters. It can also be used to
distinguish between cells from different operators on two country
borders. It is essential for the locating algorithm that the correct
neighboring cells are evaluated. BCC is used as protection against
co-channel interference. For this purpose, BCC must be allocated
as wisely as possible. It is recommended that all cells in a given
cluster use the same BCC. If a call setup in another country or a
different PLMN is permitted, the parameter NCCPERM
supersedes NCC.
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GSM BSC Operation
BCCHNO: Absolute RF channel number for BCCH. Numeral 1 124 in GSM900, 128 – 251 in GSM800, 512 - 885 in GSM1800,
512-810 in GSM1900 and 975-1023 in GSM900 G-band.
Remember that the BCHs and CCCHs are transmitted over the
BCCH.
Figure 4-9. BCCHNO
AGBLK: Number of reserved access grant blocks. Numeric 0 - 7.
Numeric 0 - 2 for SDCCH/4.
Number of CCCH blocks reserved for the AGCH. The remaining
CCCH blocks are used as PCHs. The parameter is valid only for
internal cells, that is, cells belonging to the current BSC. Within
Ericsson´s GSM system, access grant messages have priority over
paging messages, but if Cell Broadcast is to be broadcast then
AGBLK must be equal to 1. During this reserved CCCH block the
MS is told to listen to the cell.
DOWNLINK
BCH51 - frame (235.4ms)
F
F
F
F
F
S
S
S
S
CS
CCCH C CCCH CCCH C CCCH CCCH C CCCH CCCH C CCCH CCCH
C
C
C
C C BCCH B0 C C B1
C
C
C
B2
B4
B6
B3
B5
B7
B8
HH
HH
HH
HH
HH
0
5
10
15
20
25
30
35
40
45
50
Figure 4-10. Block for AGBLK
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MFRMS: Multi-frames period. Numeric 2 - 9. Defines the period
of transmission for PAGING REQUEST messages to the same
paging group. The parameter is expressed as the number of CCCH
multi-frames. The parameter is valid only for internal cells. Each
MS, according to its IMSI number, belongs to a specific paging
group. Dependent on the IMSI-number, an MS is allocated on one
of the CCCH-blocks in a set of multi-frames. Paging signals to this
MS are then exclusively sent in this CCCH-block. The set of multiframes is determined by MFRMS. Since MFRMS can be set
between 2 and 9, and the number of CCCH blocks within a multiframe is 9, it is possible to have from 18 to 81 paging groups.
BCCHTYPE: Identifies the type of BCCH to be used, this is only
applicable to internal cells:
COMB
Indicates that the cell has a combined BCCH and
SDCCH/4.
COMBC
Combined with the CBCH. Indicates that the cell
has a combined BCCH and SDCCH/4 with a CBCH
subchannel.
NCOMB
Indicates that the cell does not have a combined
BCCH and SDCCH/4.
DEFINITION OF SUBCELLS
RLDSI: CELL=cell;
This command creates a subcell structure for one or several cells.
The cell must be internal, and can be in the state ACTIVE or
HALTED.
If a cell is configured with at least two frequencies, it can be split
into two subcells - an overlaid subcell and an underlaid subcell.
More than one frequency can be assigned to a subcell. In the BSC,
subcells are denoted by the parameter SCTYPE. SCTYPE can be
UL for underlaid or OL for overlaid subcell. Nowadays the BCCH
is supported in both UL and OL cells.
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GSM BSC Operation
Underlaid
BCCH, SDCCH, TCH
Overlaid
BCCH, SDCCH, TCH
BTS
Figure 4-11. Create a SubCell
CHANNEL GROUPS
RLDGI:
CELL=cell,
BAND=band;
CHGR=chgr,
SCTYPE=sctype,
This command is used to specify channel groups for a cell or
subcell. If a subcell structure is specified with the command
RLDSI, the parameter SCTYPE must be included in this command.
CHGR: Channel group. Numeral 0-15. Maximum 16 channel
groups can be specified per cell.
SCTYPE: subcell type
UL= underlaid
OL= overlaid
BAND: GSM800, GSM900, GSM1800 and GSM1900 band in
Multiband Cells
DISCONTINUOUS TRANSMISSION DOWN-LINK
RLCXC: CELL=cell, DTXD=dtxd;
DTXD: Discontinuous transmission down-link. On or off. Where
off is the default.
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This command enables or disables the status of discontinuous
transmission down-link for a cell. Valid for internal cells only.If
nothing is said into an MS microphone, there is no point sending
anything at all in the air. When the Discontinuous Transmission
(DTX) feature is used, the system only transmits when speech is
detected over the connection. This decreases the power
consumption in the MS and in the BTS and reduces the amount of
energy emitted into the air.
Figure 4-12. DTX
CONFIGURATION POWER DATA FOR CELL OR SUBCELL
RLCPC: CELL=cell, SCTYPE=sctype, MSTXPWR=mstxpwr,
BSPWRB=bspwrb, BSPWRT=bspwrt;
MSTXPWR: Maximum transmit power in dBm for an MS on a
connection.
BSPWRB: Base Station nominal output power in dBm, for the RF
channel number with the BCCH.
BSPWRT: Base Station nominal output power in dBm, for the RF
channels without the BCCH.
This step is used to define or change configuration power data in a
cell or a subcell. The indicated power is the nominal power of the
transmitter in the BTS, not the ERP. If a subcell structure exists,
the parameters MSTXPWR and BSPWRT should be specified for
each subcell. If the cell is external, only parameter MSTXPWR is
valid with CELL.
FREQUENCY HOPPING DATA
RLCHC: CELL=cell,
MAIO=maio;
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CHGR=chgr,
HOP=hop,
HSN=hsn,
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GSM BSC Operation
This command is used to change the frequency hopping status and
hopping sequence number for a channel group. The CHGR
parameter is mandatory if channel groups other than 0 exist. The
command is only valid for internal cells.
CHGR: Channel group. Numeral 0-15.
HOP: Frequency hopping status. On or off.
(The hopping type is defined in the MO = TG in the command
RXMOC and parameter FHOP wirt either BB or SY)
HSN: Hopping sequence number. Numeral 0-63.
HSN= 0 is cyclic hopping
HSN= 1-63 identifies a pseudo-random sequence
MAIO: Mobile Allocation Index Offset.
Maximum 16 Mobile Allocation Index Offsets (MAIOs) per
channel group. The MAIOs will form a list. All MAIOs in the list
must be unique.
Numeral 0 - 31
CONFIGURATION FREQUENCY DATA
RLCFI: CELL=cell, CHGR=chgr, DCHNO=dchno;
If more frequencies than the BCCHNO are added to the cell, these
frequencies should be defined separately. The cell in question can
be ACTIVE or HALTED. If subcells exist, new frequencies are
added to the channel group (CHGR).
Figure 4-13. Create a DCHNO
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CHGR: Channel group. Numeral 0-15.
DCHNO: ARFCN (Absolute RF channel number). The frequency
below can be allocated to a maximum of 31 DCHNO per channel
group, except for Channel Group 0, which allows only 30. Overall
a maximum of 127 DCHNO per cell is allowed.
Figure 4-14. Group of Frequency
CONFIGURATION CONTROL CHANNEL DATA
RLCCC: CELL=cell,
CBCH=cbch;
TN=tn,
CHGR=chgr,
SDCCH=sdcch,
TN: Time slot Number. Numeral 0-3 for a normal cell. Numeral 0
or 2 for an extended range cell. System default value= 2.
CHGR: Channel group. Numeral 0-15.
SDCCH: Required number of SDCCH/8. Numeral 0-32. Numeral
0-7 when parameter CCHPOS is set to BCCH. Numeral 0-3 when
parameter CCHPOS is set to BCCH and the cell is an extended
range cell.
CBCH: Cell Broadcast Channel.
CBCH = YES should be included in one SDCCH/8 for the cell or
channel group.
CBCH = NO indicates that no SDCCH/8 for the cell or channel
group should include CBCH.
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GSM BSC Operation
RLCCC:CELL=HLM1,CHGR=0,SDCCH=9,TN=2&&4;
Assign 9 SDCCH/( on Time Slots 2 through 4 for each
Carrier in Channel Group 0 in cell HLM1.
TN
0
1
2
3
4
5
6
7
C0
B
T
S
S
S
T
T
T
C1
T
T
S
S
S
T
T
T
C2
T
T
S
S
S
T
T
T
C3
T
T
T
T
T
T
T
T
C4
T
T
T
T
T
T
T
T
B=BCCH, S=SDCCH/8, T=TCH, TN=Timeslot Number
C0-C4= First to fifth carrier in CHGR 0
Figure 4-15. Definition of the SDCCH
MEASUREMENT FREQUENCIES
RLMFC:CELL=cell, MBCCHNO=mbcchno, LISTTYPE=listtype;
For handover possibilities, MSs must measure the signal strength
(SS) of neighboring cells via their individual BCCH (C0). A list of
BCCHs is called the BCCH Allocation List (BA List), collected by
the BSC, and transmitted to the MS.
MBCCHNO: Is the Absolute RF Channel Number (ARFCN)
for measurement on BCCH. Numeral 1 - 124 in GSM 900, 512 885 in GSM 1800, 512 - 810 in GSM 1900. and 975-1023 in
GSM900 G-band It represents the BCCH frequencies to be
measured on by MSs in the cell.
In dual mode systems, frequencies from both systems can be used
simultaneously.
LISTTYPE: Indicates if the list of measurement frequencies is to
be used by the MS for measurements in IDLE mode or for
measurements in ACTIVE mode.
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Figure 4-16. Mensuration of the Neighbors
CELL LOCATING DATA
RLLOC:
CELL=cell,
SCTYPE=sctype,
BSPWR=bsprw,
BSTXPWR=bstxpwr, BSRXMIN=bsrxmin, BSRXSUFF=bsrxsuff,
MSRXMIN=msrxmin, MSRXSUFF=msrxsuff;
BSPWR: Base Station Effective Radiated Power (ERP) for the
absolute RF channel in the cell, defined for BCCH. Numeral 0-80
(dBm).
BSTXPWR: Base Station Effective Radiated Power (ERP) for the
absolute RF channel in the cell, not defined for BCCH. Numeral 080 (dBm).
BSRXMIN: Minimum estimated up-link signal strength level
threshold. Numeral 0-150 (dBm).
The estimated up-link signal strength of a neighboring cell is
compared to this threshold so as to be considered for handover. The
estimation is made by calculating the down-link path loss and
subtracting it from the mobile output power.
MSRXMIN: Minimum down-link signal strength level threshold.
Numeral 0-150 (dBm).
The down-link signal strength of a neighboring cell is compared to
this threshold so as to be considered for handover.
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GSM BSC Operation
BSRXSUFF: Sufficient estimated up-link signal strength level
threshold. Numeral 0-150 (dBm).
The estimated up-link signal strength of a neighboring cell is
compared to this threshold so as to be considered for further
ranking according to pathloss.
MSRXSUFF: Sufficient down-link signal strength level threshold.
Numeral 0-150 (dBm).
The down-link signal strength of a neighboring cell is compared to
this threshold to be considered for further ranking according to the
path loss.
NEIGHBOR RELATIONS
RLNRI: CELL=cell, CELLR=cellr, SINGLE;
It is mandatory to define neighbor relationships. These
relationships control the handover between cells.
CELLR: Related cell. Max. 7 characters.
SINGLE: Defines the single relationship between the cells.
The parameter SINGLE is only given if the relation is one-way
from CELL - CELLR. This means that handover can be made from
CELL to CELLR. Default is mutual which means that handovers
are allowed in both directions.
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8
7
6
SKIP INDICATOR
0
0
0
5
4
3
2
1
PROTOCOL DISCRIMINATOR
1
Octet 1
DTX
RXLEV-FULL Serving Cell
USED
MEAS
RXLEV-SUB
Serving Cell
VALID
RXQUAL-FULLRXQUAL-SUBNC
Serving Cell
Serving Cell
Octet 2
NC
RXLEV-NCELL 1
BSIC-NCELL 1
BCCH-Freq NCELL 1
BSIC-NCELL 1
Octet 5
BA
USED
Spare
Spare
1
0
Message Type
1
0
Octet 0
Number 2
Octet 3
Octet 4
Octet 6
Octet 7
Octet 8
Octet 9
Octet 10
Number 3
Octet 11
Octet 12
Number 4
RX 5
RXLEV-NCELL 5
BCCH Freq Ncell 5
BSIC-NCELL 5
BF 5
RX 6
RXLEV-NCELL 6
BCCH Fr 6
BF 6
BSIC-NCELL 6
Octet 13
Octet 14
Octet 15
Octet 16
Octet 17
Figure 4-17. MR
SYSTEM INFORMATION SACCH AND BCCH DATA
RLSSC: CELL=cell, ACCMIN=accmin, CCHPWR=cchpwr,
CRH=crh, DTXU=dtxu, NCCPERM=nccperm, RLINKT=rlinkt;
ACCMIN: Minimum received signal level in dBm at the MS for
permission to access the system. Numeral 47 - 110 (dB).
47 =
48 =
108 =
109 =
110 =
greater than -48dBm
- (49 to 48) dBm
- (109 to 108) dBm
- (110 to 109) dBm
less than -110 dBm
CCHPWR: Maximum transceiver power level (TXPWR) in
dBm a MS may use when accessing the system on CCCH or
SDCCH.
GSM 800/900 Numeral 13 - 43 (dBm) in steps of 2
GSM 1800/1900: Numeral 4 - 30 (dBm) in steps of 2
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The parameters CCHPWR and ACCMIN are used to calculate the
cell access criterion C1, explained in Chapter 2.
CRH: Cell Reselect Hysteresis. Receiving SS (RXLEV) hysteresis
in dB for required cell reselection over LA border. Numeral 0 - 14
(dB) in steps of 2
This parameter prevents unnecessary location updating and
jumping between different cells connected to separate LAs when
the idle MS is moving along the border between two LAs.
DTXU: Discontinuous transmission up-link. DTX is implemented
as shown in Figure 4-17 to decrease the power consumption in the
MS and to reduce the carrier-to-interference level (C/I). During
speech pauses, the power consumption is reduced and when the
first word is spoken, the power returns to normal.
0 = The MSs may use up-link discontinuous transmission.
1 = The MSs will use up-link discontinuous transmission.
2 = The MSs will not use up-link discontinuous transmission.
POWER
SLEEP
SPEECH
POWER
SLEEP
SPEECH
SILENCE
POWER
SPEECH
SILENCE
Figure 4-18. Discontinuous Transmission
NCCPERM: PLMN color codes permitted. Numeral 0 - 7. They
define the allowed NCCs on the BCCH carriers for which an MS is
permitted to report measurement results. Up to 8 NCCs can be
defined. These replace previously defined NCCs. To enable a
mobile to set up a call to cells with NCC equal to four, NCCPERM
should be set to four. See Figure 4-19.
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Country A
NCC = 2
f 28
f 30
f 31
f 29
f 15
f 17
f 16
f 20
f 21
f 18
f5
f 32
f 31
f1
f 75
f3
f4
Country C
NCC = 1 & 4
f 13
f2
f 30
f 13
Country B
NCC = 3
f3
f 12
f 76
Figure 4-19. Handover Allowed According to the Parameter NCCPERM
RLINKT: Radio Link Time-out. Numeral 4 - 64 (number of
SACCH periods) in steps of 4. The amount of time before an MS
disconnects a call due to failure in decoding SACCH messages. If
the number of consecutively lost SACCH blocks on the down-link
is equal to the parameter RLINKT, the MS initiates the clear
procedure.
SYSTEM INFORMATION BCCH DATA
RLSBC: CELL=cell, CB=cb, ACC=acc, MAXRET=maxret,
TX=tx, ATT=att, T3112=t3212, CBQ=cbq, CRO=cro, TO=to,
PT=pt, SLOW;
ACC: Access Control Class. This defines which access classes are
barred. An access class can be assigned to normal subscribers or to
subscribers with priority such as emergency services or testequipment. Up to 16 access classes can be defined.
0-9
10
11 - 15
CLEAR
LZT 123 3801 R7A
Access classes that are barred (normal subscribers)
Emergency call not allowed for MSs belonging to
classes 0 - 9
Access classes that are barred (special subscribers)
No access classes are barred
© 2006 Ericsson
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GSM BSC Operation
MAXRET: Maximum retransmissions. Numerals 1, 2, 4 or 7. This
defines the maximum number of retransmissions allowed for an
MS when accessing the system. This implies that the same access
is sent up to MAXRET times in case of access failure. The time
interval between accesses is determined by the parameter TX.
TX: TX-integer. Numerals 3 - 12, 14, 16, 20, 25, 32, 50. Defines
the time interval in number of TDMA frames the mobile may use
to spread random accesses. The waiting time between two access
attempts is due to the time interval defined by TX and the CCCH
configuration.
ACCESS 1
ACCESS 2
ACCESS 3
ACCESS 4
R R RR R R
A A AA A A
C C CC C C
H H HH H H
Wait
R R R RR R R
A A A AA A A
C C C CC C C
H H H HH H H
Wait
Wait
Figure 4-20. Choice of RACH When TX Is Set to 12
ATT: Attach-detach allowed.
NO: Mobiles in the cell are not allowed to apply IMSI
attach/detach.
YES: Mobiles in the cell should apply IMSI attach/detach.
The IMSI attach/detach operation is an action taken by an MS to
indicate to the network that it has entered an active/inactive state.
When an MS is powered off, an IMSI detach message is sent to the
MSC/VLR. When an MS is powered on, an IMSI attach message is
sent. A flag is set in the VLR indicating the present state of a
certain MS. There is no need to page a detached MS.
T3212: Time-out value. Numeral 0 - 255 (decihours). Defines the
time-out value controlling the periodic registration procedure, that
is, when notifying the availability of the MS to the network. If no
registration is performed before the time-out and the guard period
set in the MSC expire, the MS will be registered as detached
(implicit detached).
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0 = Infinite time out
1 = 0.1 hours
*
255 = 25.5 hours
CB: Cell Bar Access. If a cell is barred, it will be ignored by an
MS in idle mode. However, an active MS can handover to it. This
feature can be applied to all types of internal cells.
NO, the cell is not barred
YES, the cell is barred
CRO: Cell Reselect Offset. Defines an offset to encourage or
discourage MSs to reselect the cell. Numeral 0 - 63.
0 = 0dB; 1 = 2dB; . . . 63 = 126dB
TO: Temporary Offset. Defines a negative offset applied to CRO.
Numeral 0 - 7. 0 = 0dB; 1 = 10dB; …6 = 60dB; 7 = infinite
PT: Penalty Time. Defines the duration for which the TO is
applied.
Numeral 0 - 31. 0 = 20 s; 1 = 40 s; 30 = 620 s
The value 31 indicates that CRO is negated and that TO is ignored.
These parameters, CRO, TO, and PT control the selection or
reselection of a cell, according to GSM Phase 2.
BSC LOCATING DATA
RLLBC:SYSTYPE=systype, TINIT=tinit, EVALTYPE=evaltype;
SYSTYPE: System type. Identifier GSM900, GSM1800, or
GSM1900.
TINIT: Time after initiation. Minimum time before handover is
allowed on an initial call or after handover. Numeral 0-120
(SACCH periods).
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GSM BSC Operation
After a new dedicated channel assignment, the BSC starts the timer
TINIT. The assignment can be any dedicated channel such as
SDCCH or TCH. It does not matter if it occurs directly after a call
setup or a successful handover. The Call Process performs the
assignment and starts the timers. For the time specified by TINIT,
the BSC does not allow handover. Once TINIT expires, the BSC
allows handovers again. The purpose of TINIT is to prevent the
MS from jumping from one cell to another because a frequent
change of the radio channel deteriorates the overall quality of the
connection and increases the processor load.
EVALTYPE: Evaluation type. Numeral 1 or 3.
1= Cell ranking according to the Ericsson1 locating algorithm.
3= Cell ranking according to the simplified and optimized
Ericsson3 locating algorithm.
ERICSSON1
In the Ericsson1 algorithm, the candidate cells pass three stages:
the M-criterion, the K-criterion, and the L-criterion .
M-algorithm
Accepted
cells
Min
Suff
K-algorithm
L-algorithm
Ranked
better
Path loss
Ranked
worse
Unaccepted
cells
Cells ranked
according to
L-criteria
Cells ranked
according to
K-criteria
PO-Cell list
Figure 4-21. Ericsson 1 Locating Algorithm
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The M-criterion
In the first step, the system checks whether a candidate meets a
minimum requirement or not. Every cell that is a potential
candidate must provide a signal strength above a certain threshold
on both the down-link and the up-link. For the down-link
connection, there is a minimum threshold level MSRXMIN. This
is the threshold of MS_RXLEV (SS the MS must receive from
neighboring cells). For the up-link, the BTS must receive a signal
strength above the threshold BSRXMIN (BTS received minimum).
If one of the two values is below the corresponding threshold, the
candidate will not be accepted for further evaluation. The list with
the accepted cells is forwarded to the K-criterion stage.
The K-criterion
All candidates in this phase are checked against another threshold,
the sufficient signal strength level, that is, MSRXSUFF for the
down-link and BSRXSUFF for the up-link. As with the Mcriterion, the values for both the up-link and the down-link must be
above the corresponding MSRXSUFF and BSRXSUFF thresholds,
respectively. If both values are above the threshold, they are
marked as L-cells, those below the threshold are marked as Kcells.K-cells are ranked according to signal strength. In the K-list,
the cell providing the highest signal strength is ranked first. In the
end, the K-list is appended to the L-list. K-cells always have an
inferior position to L-cells.
The L-criterion
All cells above the sufficient level (BSRXSUFF, MSRXSUFF) are
ranked according to path loss. On the down-link, path loss L is
defined as:
L = BSPWR - MS_RXLEV
Where BSPWR applies to the case of the serving cell.Concerning
neighboring cells, BSPWR is replaced by BSTXPWR.
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GSM BSC Operation
MS_RXLEV
BSTXPWR
pathloss L
MS
distance to BTS
Figure 4-22. L Cell Ranking
On the up-link, the path loss L is defined as:
L = MSTXPWR - BS_RXLEV
The cell with the lowest path loss is ranked first. Ranking
according to path loss shifts the nominal point of handover to the
geographical center between two cells. Thus, interference can be
reduced.
The following example (Figure 4- 23) illustrates this effect. A large
cell, A, with high output power (ERP) BSPWR and a small cell, B,
with small output power (ERP) BSPWR are neighbors. For
simplification reasons it is assumed that RXLEV is above
MSRXSUFF in all places. Only down-link signal strength is
considered. The MS moves on the axis between the centers.
Shadowed areas indicate the areas where both cells are considered
L-cells. In the white area, they are ranked as K-cells. First, the MS
belongs to cell A; a handover to cell B is performed as soon as the
MS moves out (on the axis) of the shadowed area of cell A.
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Cell A
Cell B
RXLEV
point of HO in K-ranking
point of HO in L-ranking
L
Figure 4-23. K Cell Ranking
ERICSSON3
The Ericsson1 algorithm is complex. This means that it is difficult
to optimize. Ericsson2 is a much simpler algorithm without
optimizing possibilities. A new locating algorithm, Ericsson3,
which is easier to handle (less parameters) and easier to understand
than Ericsson1, but still possible to optimize, has been introduced
and replaces Ericsson2.
• Only a simplified K-ranking is performed. The double ranking
criteria are removed.
• Candidates are ranked with respect to absolute signal strength,
and not according to their relative signal strength level.
• A parameter to classify a serving cell as a high signal or a low
signal cell is introduced. If the serving cell is a high signal cell,
a high hysteresis is used and if it is a low signal cell a low
hysteresis is used.
• Both down-link and up-link signal strength is used to select the
appropriate hysteresis level.
• Only one offset parameter per cell to cell relation is used.
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GSM BSC Operation
Basic Ranking
The basic ranking is performed by the Locating function.
Absolute signal strength is used when ranking cells. Ranking is not
performed in relation to any minimum level or sufficient level. All
cells are ranked in the same list. The parameters, MSRXSUFF and
BSRXSUFF, are not used by Ericsson3.
Cells are not classified as K- or L-cells. Instead the serving cell is
classified as a high signal or a low signal cell, depending on the
level, HYSTSEP. If the down-link signal strength is below
HYSTSEP, the serving cell is classified as a low signal cell.
Otherwise it will be classified as a high signal cell.
If the serving cell is a high signal cell, a high hysteresis, HIHYST,
is used and if it is a low signal cell, a low hysteresis, LOHYST, is
used. The hysteresis value is subtracted from the ranking value for
the neighboring cell.
CONNECTION OF CELL TO TRANSCEIVER GROUP
RXTCI: MO=mo, CELL=cell, CHGR=chgr;
On completion of the OPI: BSC, Internal Cell, Define, the BSC
knows the cell as a set of data. However, the cell does not have a
connection to a BTS. No BTS is configured yet, according to the
parameters as defined in configuration power data, control channel
data, or frequency data. Therefore, the cell must be connected to a
TG before it is activated. A TG is indicated to the cell as an MO
(refer to Chapter 3) and a CHGR. Refer to Figure 4-24
BSC
MO = TG
TRX 1
Cell Data File
CHGR=0
CHGR=1
TRX 2
Figure 4-24. Connection of Channel Groups to Transceiver Groups
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CELL STATE
RLSTC: CELL=cell, CHGR=chgr, STATE=state;
CHGR: Channel group. Numeral 0-15
STATE: The state of the cell. Active or halted.
When defining cell data, the state of a cell is HALTED (off air).
After cell data definition, the state of the cell must be changed to
ACTIVE (on air). Alternatively, an individual CHGR can be
activated. During cell activation, the cell data for description and
configuration is downloaded to the connected TG. The purpose of
the cell state is to control the data input to the cell to minimize the
impact on ongoing traffic. Very important data can only be
changed in the HALTED state, for example, cell description data
(CGI, BCCHNO, etc.).
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Intentionally Blank
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5 Performance Measurement and Supervision
Objectives:
Execute performance measurement and supervision features
that are available in BSS using appropriate command and
WinFiol.
ƒ Define supervision and recording processes in the BSC
Figure 5-1. Objectives
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GSM BSC Operation
Intentionally Blank
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MOBILE TRAFFIC RECORDING (MTR)
MTR initiates the recording of traffic events and of measurement
data, collected on the radio interface. MTR collects event data,
measurement data for a specific connection, and cell translation
data for all the cells in the BSC. The recording is initiated in the
MSC (or OSS) and starts in the BSC at the reception of the
message Trace Invocation from the MSC (or the GSM phase 2
message MSC Invoke Trace making it possible to trace the MSCs
of other manufacturers and Ericsson’s BSCs). Data is continuously
output on sequential files MTRFIL00-MTRFIL63 in the File
Management Subsystem (FMS). Event data can also be output as
an alphanumeric printout, if required. The function terminates
when the connection is terminated in the BSC, that is, when a
handover is made to another BSC, at call disconnection, when the
recording file is full, or at system restart.
The recording is performed per MS connection. Initiation and
specification of the recording type, the output device, and the
recording reference are made in the MSC and are transferred to the
BSC per MS connection. There are two types of recordings:
•
•
Recording of event data only
Recording of both event and measurement data
Recordings stored in MTRFIL contain the data for a specific MS
connection:
Administrative Data
•
•
•
•
•
•
Exchange identity
Date
Time
File format revision information
Recording reference
Recording type
Event Data
Date / Time / Event where the event is:
•
•
•
•
•
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Message of Inter cell intra BSC handover
Message of Intra cell handover
DTAP message sent down and up-link
Handover cell candidate list
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GSM BSC Operation
•
•
•
•
•
•
Message of SAPI 3
Message of Connection release
Release indication not received, timer T3109 expired
Channel release
Release indication
Clear command
Measurement Data
•
•
•
Measurement report
Pathloss criterion
Signal strength ranking
Cell Translation
•
Translation of cell representation to CGI
The analysis for MTR should be held in MSC and uses the
following command:
MGBRI:IMSI=
,RTY=
,RR=
,ACCT=
;
Where:
RTY, Recording type
1=
2=
3=
alphanumeric output of events only
alphanumeric output of events and file output of events and
measurement data
file output of events and measurement data
RR, Recording reference 0-63 (MTRFIL 0//63)
Recording reference for the identification of IMSI in the recording
output in the BSC. Also used as a reference to the subfile for the
recorded data, for example, MTRFIL01.
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ACCT, Access type
TCN
OCN
OCE
LUN
LUP
MSA
MSD
SSP
TSM
OSM
LCS
ALL
Mobile-Terminating Call
Mobile-Originating Call
Mobile-Originating Emergency Call
Normal Location Updating
Periodic Location Updating
IMSI Attach
IMSI Detach
Supplementary Service Procedure
Mobile-terminating short message transfer
Mobile-originating short message transfer
Location services
All Types of Access
After configuring what’s information the kinds that wishes to
analyze and to define the file MTRFIL wished to save these data,
the nearby step is to seek this file in IOG:
INMCT: SPG=
;
This command initiates the use of file management commands in
the specified support processor group in IOG.
INFIP;
Execute printout of a list of all files (MTRFIL) on a certain volume
without printing the attributes. Applicable only for internal
volumes, that is hard disk volumes.
IOIFP: file=
;
This command prints the status of the sub files.
IOFAT: File=
, HEX;
This command executes output of a specified file (MTRFIL),
single or subfile, on a specified alphanumeric device
OPIs to follow:
Mobile Telephony, BSC Recording, Initiate in MSC
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GSM BSC Operation
CELL TRAFFIC RECORDING (CTR)
CTR is initiated by command from either the OSS or the BSC.
Only one CTR can be performed at a time in the BSC. The
initiation order is sent with a number of command parameter values
and the function is administered with respect to what type of
recording it is, what triggering event type, and the time scope of the
recording. Dynamic buffers are allocated and a file is seized for the
output. Buffer handling and writing to the output file are similar to
that of an MTR.
When the recording is initiated, the aim is to start the recording for
a number of connections in a certain cell. The recording is started if
the triggering event for the connection is accomplished and if there
is enough recording capacity available. 16 connections can be
recorded simultaneously, in one file (CTRFILE) stored in FMS.
The events included in a triggering event type are listed below. If
the parameter analysis or the allocating resources do not function
satisfactorily, an appropriate fault code is given. The command to
start CTR is:
RATRI:CELL=C1021, EVENT=CA, DTIME=10,
RTYPE=EV&ME, TIMEW=15, RAREA=BSC;
EVENT: Event can have four different triggering types: Cell
Access (CA), Connection Release (CR), HandOver (HO) and Trace
Invocation (TI). Below is a list of subclasses for each event.
CELL ACCESS
•
•
•
•
•
Call from MS (normal or emergency)
Page response
Incoming inter and intra BSC handover
Assignment to another cell
Trace invocation
CONNECTION RELEASE
•
•
•
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Disconnect order, normal and abnormal release (CLEAR
COMMAND)
Outgoing inter BSC handover
Trace invocation
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HANDOVER
•
•
•
•
Incoming inter and intra BSC handover
Outgoing inter and intra BSC handover
Outgoing intra cell handover
Trace invocation
TRACE INVOCATION
•
Trace invocation
DTIME: The time duration for recording. Specified as 1 through
60 minutes.
RTYPE: The recording type. Specified as Events (EV) or Events
and Measurements (EV&ME).
TIMEW: Specifies a time window from 2 to 30 seconds. This
window is used for measurements. If TIMEW is set to 10, the
recording function will output 5 seconds prior to the event, and 5
seconds after the event.
RAREA: Recording area.
CE
NCE
BSC
Recording within access cell
Recording within access cell and defined neighboring cells
Recording within the BSC
After configuring what’s information the kinds that wishes to
analyze and to define the file CTRFIL wished to save these data,
the nearby step is to seek this file in IOG:
INMCT: SPG=
;
This command initiates the use of file management commands in
the specified support processor group in IOG.
INFIP;
Execute printout of a list of all files (CTRFIL) on a certain volume
without printing the attributes. Applicable only for internal
volumes, that is hard disk volumes.
IOIFP: file=
;
This command prints the status of the sub files.
IOFAT: File=
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GSM BSC Operation
This command executes output of a specified file (CTRFIL), single
or subfile, on a specified alphanumeric device
OPIs to use:
BSC, Cell Traffic Recording, Initiate
BSC, Cell Traffic Recording Data, Print
BSC, Cell Traffic Recording, End
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CHANNEL EVENT RECORDING (CER)
CER provides the possibility to monitor the radio network
channels. The recording is intended to supply enough information
for the evaluation of the Differential Channel Allocation, Idle
Channel Measurement, and Channel Administration functions. The
recording result can be interpreted via a post-processing program.
CER makes it possible to record the changing of interference levels
on idle TCHs, as well as the behavior of channels, using Different
Channel Allocation strategies. The operator is able to monitor the
channel status by obtaining the recorded data for the channel
events. The recording can be active on 16 cells maximum.
The recording data is output to a file in FMS, CERFIL 00//15. The
recording is stopped when the time of the initiate command has
expired, when the end command is given, or at a restart.
RACEI: CELL=cell, DTIME=dtime;
DTIME: is the time for the Recording to be active between 1 ninute
and 10 hourrs (1.600)
A result printout showing cell designation, file reference, and
duration is generated at the recording initiation.
When the recording for a cell is started, an administrative record is
generated and stored. It contains the date and time of the recording
initiation, which BSC and cell the recording is active for, and the
Differential Channel Allocation status. Initially, the states of all
channels in the cell are recorded, including all parameters
describing the channel. Records are also produced for priority
profile data and channel allocation profile data at the initiation of
the function.
At the initiation of the recording function, a signal is sent to Idle
Channel Measurement and Traffical Handling of Logical Channels,
informing that recording will start on a specific cell with a specific
recording reference. Subsequently an event record will be produced
for each channel in the cell every time a channel event occurs.
Recorded channel events include: changing of interference level,
allocation, creation, deletion, blocking, deblocking, and releasing
of a channel
With the event ‘changing the interference level’, the channel
individual, time, and new interference band are recorded.
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GSM BSC Operation
When a channel administration event occurs, that is, creation,
deletion, blocking, deblocking, or releasing of a channel, the
channel individual, time, and channel result are recorded. Channel
result indicates which of the channel administration events
occurred.
With a channel allocation event this data is recorded, if valid for
the event:
•
•
•
•
•
•
•
Channel individual
Time
Channel allocation profile
Selection type
Priority level
Resource type(s)
Channel allocation result(s)
The recorded data is collected and stored on a binary coded file.
When the recording is concluded, an administrative record is
generated. It includes the time, the number of recorded records,
information about changes in the priority profile data, and the
differential channel allocation status at the recording. Post
processing of the file is necessary to create useful information from
the recorded data.
After configuring what’s information the kinds that wishes to
analyze and to define the file CERFIL wished to save these data,
the nearby step is to seek this file in IOG:
INMCT: SPG=
;
This command initiates the use of file management commands in
the specified support processor group in IOG.
INFIP;
Execute printout of a list of all files (CERFIL) on a certain volume
without printing the attributes. Applicable only for internal
volumes, that is hard disk volumes.
IOIFP: file=
;
This command prints the status of the sub files.
IOFAT: File=
, HEX;
This command executes output of a specified file (CERFIL), single
or subfile, on a specified alphanumeric device
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The RACEP command can be issued to obtain information about
the recording data for the cells in which the recording is active. The
printout specifies the active cell, the file reference, and the time.
CER is terminated either by the command RACEE, or when the
time for the recording has elapsed. A printout is issued stating why
the recording was terminated.
OPIs to follow:
BSC, Channel Event Recording, Initiate
BSC, Channel Event Recording, End
BSC, Channel Event Recording, Print
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GSM BSC Operation
ACTIVE BA-LIST RECORDING
The function Active BA-list Recording provides the facility to
collect information from the measurement results about both
defined and undefined neighboring cells, connected to the
frequencies included in the active BA-list. As well as cell-based
recordings, sub-cell and channel group can be specified when
setting the recording parameters. In addition, it is possible to add
test frequencies to the active BA-list. Every combination will be
recorded. The thresholds define which counters should be updated.
In a network it is important to specify an adequate number of
neighboring cells (n-cells) in the BCCH allocation (BA) list in the
system information. Too many n-cells in the BA-list provide less
accurate measurement results from the mobiles to be used by the
Locating algorithm to improve the quality of the network. Too few
n-cells have a negative impact on the quality of the network, which
may lead to bad speech quality and an increased number of
dropped calls.
Up to 64 recordings are possible, but a cell can only be defined in
one recording at a time. It is possible to define one, several, or all
cells in a recording. Recording is performed per call.
The operator specifies what type of recording should be made for
all cells in the recording. The alternatives are:
1. Only defined neighboring cells should be recorded.
2. Only undefined neighboring cells should be recorded, the test
frequencies are specified.
3. Both defined and undefined neighboring cells should be
recorded, the test frequencies are specified.
An undefined neighboring cell is a cell that has not been defined as
the neighboring cell of another cell. Thus, handover cannot be
performed between the cells. The test frequencies may be the
BCCH frequency of the neighboring cell’s neighbor.
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It is possible for the operator to control when a neighboring cell or
test frequency should be recorded by specifying the absolute and/or
relative signal strength compared to that of the proper cell. This
provides the operator with the opportunity to record only the
occurrences that meet his/her quality requirements for a
neighboring cell. Four threshold values can be specified when
adding definition data to a BA-List Recording to set the relative
signal strength values required in the above-mentioned recording
requirements. Command RABDC and parameters RELSSN,
RELSSP, RELSS2N, RELSS2P,RELSS3N, RELSS3P, RELSS4N,
RELSS4P, RELSS5N and RELSS5P are used to specify the
positive and negative threshold values.
The BSC starts the recording by including the frequencies
(temporarily, only in alternative 2 and 3) to be evaluated in the BAlist of the specified cells. The BSC measures how often the cells
are perceived as neighboring cells by the mobiles.
To keep the number of frequencies in the BA list as low as
possible, only an operator-specified number of test frequencies is
added to the BA-list. (The value range of the frequency numbers is
1 to 32.) If there are more test frequencies, the BSC automatically
adds those test frequencies, after a specified time, and removes the
previously tested frequencies. This is made continuously during the
whole recording period.
The measurements are made down-link. The command RABII is
used to activate a RID (Recording Identity) required to define a
particular BA-List recording. RABDC is then used to add
definition data for a particular recording. RABRI is the command
used to initiate a recording for a certain RID and give the duration.
OPIs to follow:
BSC, Active BA List Recording Definition, Initiate
BSC, Active BA List Recording, Initiate
BSC, Active BA List Recording, Administer
BSC, Active BA List Recording Report, Initiate
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GSM BSC Operation
FREQUENCY ALLOCATION SUPPORT (FAS)
Frequency Allocation Support (FAS) is a recording tool measuring the
up-link signal strength for all the cells and frequencies, specified by
the operator in the recording as shown in Figure 5-2. The operator can
order an FAS recording for up to 150 frequencies for one, several, or
all cells in the BSC. A maximum of 10 FAS recordings can be
initiated per BSC and a cell can only belong to one recording at a
time.
OPI’s to follow:
BSC, Radio Interference Recording, Initiate
BSC, Radio Interference Recording Configuration, Initiate
BSC, Radio Interference Recording, Administer
BSC, Radio Interference Recording Report, Initiate
Figure 5-2. FAS environment
The operator starts by defining the recording. The Recording
Definition contains a list of cells and/or a list of frequencies. If a
specified frequency cannot be measured by the TRXs in the cell,
that frequency is discarded and no measurements are made.
The operator continues by initiating the configuration of the TRXs,
according to the settings in the FAS recording. The BSC configures
the frequencies on which the TRXs will measure, in the cells
specified in the recording order. To configure a TRX, the TRX
must be in operation. In addition, the subordinate RX and at least
two TSs must have been defined and should be in operation.
At FAS recording initiation, the recording time is a maximum of
273 hours and is specified by the operator. It is possible to stop and
resume an FAS recording in order to record at a specific time each
day.
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RECORDING CONFIGURATION
Prior to starting the recording the recording individual must be set
up. RARII; this allocates a radio interference recording identity
(RID) from the BSC.
The initiation results are shown in an answer printout.
Command RARDC is given to set up the recording definition with
cells and frequencies. The command can be given several times to
create a definition. The measurement frequencies can be given as
either specific frequencies or as the option ALLOCATED.
ALLOCATED indicates that measurements should be performed
on the frequencies allocated in each cell. The frequency set that is
used in this case, contains the frequencies that are valid when the
Radio Interference Recording individual (RID) configuration is
made. RARDP can be given to print the recording definition.
The RID configuration is initiated by command RARCI. The RID
configuration includes distribution of the measurement frequencies
to the TRXs. If a cell is deactivated, it includes the setup of the
TRXs to perform the recording. Due to this a cell does not need to
be activated to be included in a recording. The command generates
a result printout, containing the configuration results.
An existing RID configuration can be modified, provided that no
recording is ongoing for the recording individual. This is
performed by first changing the recording definition (RARDC) and
then by performing an RID configuration (RARCI).
The recording individual can be released by command RARIE and
by doing so, the recording definition and the recorded data,
associated with the recording individual, are lost.
RECORDING
When an RID configuration has been made, it is possible to initiate
the RID by command RARRI.
RARRI: RID=rid, DTIME=dtime (,RESET);
DTIME: the recording lasts for a specified period of time, 1 to
16380 minutes. The recording can also be terminated by RARRE.
A printout is issued at termination
The recording is now activated and the TRXs are ordered to
measure and store the RIR data. The command generates a
printout, containing the recording order result.
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GSM BSC Operation
It is possible to resume a recording that has been terminated. The
previously collected recording data can be reset, or new recording
data can be added to the previous data.
If a fault affecting a TRX should occur during the recording, the
recording is automatically restarted as soon as the fault has been
remedied.
It is possible to print the recording details by command. The
recording details comprise the recording of the individual state. In
addition, the total recording time and the remaining recording time
are also printed, if the recording is active.
Recording Data Output
When the recording has been concluded, the command RARTI can
be given to transfer the processing and output of the recording data
to a file. The interference values are requested from the TRXs. The
results are presented on a per cell basis. If more than one TRX
report the cell data, the average value of the percentile values and
the average value of the median values for all TRXs reporting data
for the cell, are output. The number of measurements for each TRX
and the frequency are added. The measurements, made by a TRX,
are considered insignificant and are neglected if the number of
measurements for that TRX on one frequency is less than 30% of
that obtained from the TRX with the largest number of
measurements for that frequency.
The file output can be performed any time, provided that the
recording is concluded. This makes it possible to avoid
unnecessary high processor load during busy hours.
The output can be ordered several times with different percentile
values. The command generates a result printout, indicating the
validity (if the file output is successful, or if a cell reports
incomplete result) of the results, presented in the file output. The
most recent file output overwrites any previous file output.
If it is not possible for the TRXs to report the recording data for a
cell, it is indicated by the value zero for all quantities in the output
file.
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Measurement Quantities
The median and the percentile value of the interference
distribution, that is, the signal strength of every measured
frequency, concerning each TRX’s all frequencies, is reported to
the function. The value range for the median and the percentile
value is 0-63 dB and 0-1000 deci % respectively. In addition, the
report includes the number of measurements made.
The value range for the number of measurements is 0-65535.
The report for a TRX may include measurements for more than one
cell (when a TG is connected to more than one cell and the TRXs
are not dedicated to a specific cell). From the cell’s frequency list
its interesting values may be concluded.
OPIs to follow:
BSC, Radio Interference Recording, Initiate
BSC, Radio Interference Recording Configuration, Initiate
BSC, Radio Interference Recording, Administer
BSC, Radio Interference Recording Report, Initiate
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GSM BSC Operation
STATISTICS, BASED ON MEASUREMENT RESULTS
During a call the MS continuously sends measurement reports to
the BTS. This information and the BTS measurements on the uplink are sent in the measurement results to the BSC.
This function records the measurement results and provides the
operator with information. The function can be started for one cell,
or for all cells in the BSC. The recording time can be from 1
minute up to 168 hours (one week).
The measurement results include down-link measurements,
performed by the MSs, and up-link measurements, performed by
the BTSs as illustrated in Figure 5-3.
BSC
Figure 5-3.
MS and BTS Report Measurement Results on Which
Statistics Are Based
The results include statistic distribution of:
• Up-link and down-link signal strength
• Up-link and down-link signal quality
• Power level used by the mobiles
• Power level used by the BTSs
• Timing advance used on the connections
• Up-link and down-link pathloss
This feature includes the administration of the recording, the
recording, the statistics collection, the statistics post processing,
and the result output to a binary file. The collection, the post
processing and the output of the statistics can be performed later.
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In addition it is possible to record at different times and to obtain
cumulative results for example, during busy hours or for a certain
time period, and then to retrieve the cumulative results from the
last recording period.
When selecting the measurement results to be recorded, it is
possible to use either the measured values on the up- or down-link.
It is possible to specify only one measurement type for recording
(e.g. timing advance, signal strength or signal quality). In addition,
it is possible to collect correlated statistics (e.g. only measurement
results with a timing advance greater than 32). The possible types
of measurements to correlate are timing advance, signal strength,
and signal quality.
At the end of each recording the collected statistics are stored in a
binary file in the BSC. This file can be retrieved from the BSC by
the OSS for further evaluation.
RAMII; is used to allocate a measurement result recording identity
(RID).
RAMDC: RID= rid, CELL=cell, …; Where RID = MRRFIL00//09
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GSM BSC Operation
REAL TIME EVENT DATA
INTRODUCTION
The Real Time Event Data feature provides operators with access
to radio network events on a real time basis. The feature is part of
the OSS feature Real time Performance Monitoring (R-PMO), and
provides an effective and user-friendly way of monitoring network
performance in real time from the OMC site. This feature provides
the following services to GSM operators
•
•
•
Very quick and accurate feedback of the radio network
performance.
Fast monitoring of the radio network after changes have been
introduced.
Detailed event data providing links between parameter tuning
and radio network performance.
A reporting mechanism in the BSC provides information about
events in the radio network, i.e. event data on a real time basis. The
information includes raw data about TCH and SDCCH utilization,
quality measurements on UL and DL data, speech quality
measurements and successful and unsuccessful Handovers. The
requested event data is transferred via the Signaling Terminal for
Open Communication (STOC) HW in the BSC in a TCP/IP format
to the OSS.
Event data is transferred from the BSC to the OSS depending on
the requirements specified in OSS by the operator. At the OSS site,
the event data can be viewed in graphical and/or tabular form by
using the R-PMO feature. This feature provides real time feedback
from radio network design and optimization activities.
The principle of Real Time Event Data is illustrated in Figure 5-4.
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5 Performance Measurement and Supervision
R-PMO (OSS)
Performance/
Control
Agent
PM GUI
TCP/IP
2) Start Event Subscription
BSC
CNA EAM
Db
1)
TCP/IP
Activate Real Time
Event Data
(MML, RAPMI)
3) Report Events
IOG20/APG40
STOC
ROMDATA
ESIGA
APT
Figure 5-4. Real Time Event Data, BSS View
When we work with APG40, the connection with the OSS is done for
TCP/IP but when we are working with the old Hardware IOG20 the
connection with the the OSS can be done for TCP/IP or X.25.
The network performance is monitored in two different reports in
the R-PMO application:
• Traffic Report - TCH traffic, TCH utilization and perceived
congestion.
• Quality Report - TCH and SDDCH drop rates, handover success
and speech quality.
A report provides monitoring data indicating the performance for a
selected cell set. Cell sets (a collection of cells) can be created,
edited and deleted within the R-PMO application. To view the
performance of a cell set in a report, the report must be activated.
R-PMO will not receive any data from cells that do not belong to
an activated report. The report contains a table showing the current
performance measurements or monitors for each cell in the cell set.
The values are updated once a minute. The values displayed are
usually the average value during a specified time period or
resolution which can be selected in the report window. Each
monitor can also be displayed in a graph showing how the values
have changed during the last 60 minutes. An example of the graph
display is shown in Figure 5-5
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GSM BSC Operation
Activate Real Time:
RAPMI:EID=event;
RAPMI:EID=ALL;
OPI to Use:
SCS Event Reporting Performance Monitoring Subscription Status
Change by Command
RAPMI:EID=event;
RAPMI:EID=ALL;
Figure 5-5. Traffic Report Graph Representation
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5 Performance Measurement and Supervision
REPORT DETAILS
Traffic Report
The Traffic Report provides detailed information about traffic
conditions in a network and includes the following monitors:
TCH Traffic (Erlang). The average traffic in the cell. Both circuit
switched and packet switched calls contribute to the traffic level.
Subscriber Perceived TCH Congestion (%). The average
percentage of call set-up attempts that fail due to lack of resources
(TCHs and Transcoders), compared to the overall number of call
set-up attempts. Lack of TCH resources for HSCSD or GPRS is not
reported.
TCH Utilization (%). The average percentage of used capacity
compared to the available capacity ( Number of TCHs) used for
circuit and packet switched traffic.
Number of TCHs. The average number of timeslots that have been
available to use for traffic — this includes use for circuit switched,
packet switched traffic or on-demand control channels. This value
is typically rather stable since it shows the current capacity of the
cell. It will vary if timeslots are blocked (ABL, MBL etc.) or used
as on-demand control channels.
Number of busy TCHs (Peak). The highest number of
simultaneously used TCHs during the resolution time period.
Quality Report
The Quality Report provides detailed information on the
performance quality and includes the following monitors:
TCH Drop (%). The average percentage of the ongoing calls that
are dropped compared to the total number of call releases. A
dropped call is a call that has one or more TCHs which are
terminated for reasons other than handover or normal call release.
SDCCH Drop (%). The average percentage of dropped SDCCH
connections compared to the total number of released SDCCH
connections.
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GSM BSC Operation
RXQUAL UL, RXQUAL DL (%). The average percentage of
measurements that have an RXQUAL on the uplink or downlink
that is over a given threshold, compared to the overall number of
received measurements. The default threshold value is 5 for GSM,
but it can also be configured as required by the System
Administrator.
Unsatisfactory Speech Quality (%). The average percentage of
measurement results that have a Speech Quality Index (SQI) under
a given threshold compared to the number of received
measurement results. The default threshold value is 4 dbQ, but it
can also be configured as required by the System Administrator.
Handover Success (%). The percentage of successful outgoing
handover attempts compared to the total number of handover
attempts. Both inter cell and inter BSC handovers are counted for
the measurement, intra cell handovers however are not included.
TCH Traffic (Erlang). The average traffic in the cell is measured.
Both circuit switched and packet switched calls contribute to the
traffic level.
Number of Handover Attempts. The average number of handover
attempts per minute.
OPI to Use:
SCS Event Reporting Performance Monitoring Subscription Status
Change by Command
Commands
The command to activate Real Time Event Data in the BSC is:
RAPMI:EID=event;
RAPMI:EID=ALL;
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6 BSS Operations
6 BSS Operations
Objectives:
Operate and supervise the BSC using pre-defined routines
and supervision command and tools analysis of the OSS
ƒ Handle pratical fault-finding on BSC hardware using On-line
documentation
Figure 6-1. Objectives
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GSM BSC Operation
Intentionally Blank
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6 BSS Operations
SYSTEM SUPERVISION
This list of procedures is an example of what a system technician
may perform as daily, weekly, monthly, quarterly and periodic
supervision processes.
DAILY SUPERVISION
Run Daily BSC commands
Store each of the following printouts.
• The alarm list, ALLIP;
• CP working state, DPWSP;
• CP load data, PLLDP;
• Group switch status, GSSTP; (for MSC 810 have GDSTP).
• IOG node status, IMMCT:SPG=spg;
IMCSP;
END;
• System clock, CACLP;
• List of all blocked devices, STBSP:DETY=ALL;
• SP link data, EXSLP:SPG=spg;
• State of all SS7 link sets, C7LTP:LS=ALL;
• System error intensity, SYELP;
• Verify backup times, SYBTP;
• List of unused and continuously used devices, RASAP;
• List of unused and continuously used channels, RLVAP;
• Cell status, RLSTP:CELL=ALL;
• Cell resource data, RLCRP:CELL=ALL;
• Error log data, RXELP:MOTY=moty;
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GSM BSC Operation
• Managed object fault information, RXMFP:MOTY=moty;
• Managed object status, RXMSP:MOTY=moty;
This can be run as a daily command file every morning, and it can
be automatically run using the command :
IOCML:FILE=file, DATE=date, TIME=time, PROC=proc,
DAILY, IO2=io2;
Analyze the printouts, determine any possible fault situation.
Review spontaneous alarm printouts from the previous working
day.
Verify the Accuracy of the System Clock
Obtain the official time from the PSTN.
• Print system date and time, CACLP;
Verify the accuracy of the system clock. To change the time, refer
to the OPI System Clock, Inspect and Adjust.
Complete Daily Checklist
• Run daily BSC commands.
• Check the alarm printer AT-0 for proper operation.
• Check the alarm list several times during the day, ALLIP;
• Print system error intensity, SYELP;
• Print error log data, RXELP:MOTY=moty;
• Print
managed
object
RXMFP:MOTY=moty;
fault
information,
• Print managed object status, RXMSP:MOTY=moty;
Record all events in the Exchange Journal and the applicable log.
To update the Journal, refer to the OPI Keeping a Journal.
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WEEKLY SUPERVISION
Run Weekly BSC Commands
Store each of the following printouts.
• Check quality supervision parameters, DTQSP:DIP=ALL;
• Check fault supervision parameters, DTFSP:DIP=ALL;
• Print transaction logging conditions, IMLCT:SPG=spg;
MCTLP;
END;
• Network synchronization supervision data, NSDAP;
• Signaling terminal fault data, S7FLP:ST=ALL;
• Measurement program schedules, TRTSP:MP=0&&255;
• CLM control values, GSCVP;
• Digital paths, DTSTP:DIP=ALL;
• SP fault detection log, DISFP:SPG=spg, NODE=node;
• A-bis path status, RXAPP:MOTY=RXOTG;
• Cell supervision of logical channels, RLSLP:CELL=ALL;
• Seizure supervision of logical channels, RLVLP;
• Exchange supervision functions, RABLP:DETY=ALL;
Analyze the printouts, determine any possible fault situation.
Backup Commands in the Transaction Log
To print all the commands in the transaction log use the OPI MCS
Search in the Transaction Log. Store the commands on a log file
and copy to a 3.5” disk. Store for one year. (This may be done in
the Network Management Center (NMC), where the file will be
stored in the OSS). Update the Exchange Journal.
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GSM BSC Operation
Perform System Backup
Evaluate whether there is enough time to perform a manual dump
before the scheduled automatic dump. (If there is not enough time,
deactivate the automatic dumping function, refer to the command
SYBUE ).
Use the OPI Handling of New Plant Generation.
Update the Exchange Journal.
Administer Group Switch Disturbances
• Open a log file.
• Print group switch disturbances, GSDSP;
Counters will be reset after the printout.
• Analyze the printout and compare the disturbance counters to
the previous printouts.
If high values are noted, wait at least ten minutes and repeat the
procedure to determine if it is a permanent fault. If so, use the OPI
Connection Performance Test of Group Switch Disturbances.
Record the trends in the Exchange Journal.
Complete Weekly Checklist
• Run the weekly BSC commands.
• Perform a system backup.
• Backup the commands in the Transaction Log.
• Determine if the Transaction Log is active, IMLCT:SPG=spg;
MCTLP;
END;
• Print
supervision
parameters
DTQSP/DTFSP:DIP=ALL;
• Print the SP
NODE=node;
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© Ericsson 2006
fault
detection
log,
for
DIPs,
DISFP:SPG=spg,
LZT 123 3801 R7A
6 BSS Operations
• Print the state of the Digital paths, DTSTP:DIP=ALL;
• Print network synchronization supervision data, NSDAP;
• Print the CLM control values, GSCVP;
• Print the group switch disturbances, GSDSP;
• Print the A-bis path status, RXAPP:MOTY=RXOTG;
• Print the cell supervision of logical channels,
RLSLP:CELL=ALL;
Record all events in the Exchange Journal and the applicable log.
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GSM BSC Operation
MONTHLY SUPERVISION
Run Monthly BSC Commands
Store each of the following printouts.
• Print the external alarm data, AEXLP; and ALRDP;
• Print the audit functions threshold data, AFTSP:TEST=101...
• Print the CP error record, DIRCP; (for APZ 212 20)
• Print the RP event record, DIRRP:RP=ALL;
• Print the scheduled processor load measurement program,
PLSMP:MP=ALL;
• Print the size alteration store utilization, SASTP;
• Print the digital path transmission functions quality data,
DTQUP:DIP=ALL;
• Verify the backup times, SYBTP;
• Print the software recovery log, SYRIP:LOG; (Note: This can
be extremely long).
• Print the seizure supervision of devices, RASSP:DETY=dety;
• Print the dynamic BTS/MS power control,
RLBCP/RLPCP:CELL=ALL;
• Print the differential channel allocation, RLDCP;
Analyze the printouts, determine any possible fault situation.
Perform a Battery and Rectifier Check
• Using a voltmeter, measure the voltages of the battery and
record the voltages on a checklist.
• Read ammeter and voltmeter on the rectifier and record the
reading on a checklist.
Report any problems to power personnel.
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6 BSS Operations
Test Alarm Panels
• Locate the Alphanumeric Terminal (AT) configured as
COMMATT, IOIOP:IO1=ALL;
• If necessary, set attendance for the exchange, IODAC:ATT;
To test the alarm panel use the OPI Inspection and Repair of
Scanning Interface.
• If necessary, indicate unattendance, IODAC;
Complete Monthly Checklist
• Run the monthly BSC commands.
• Perform a system backup.
• Print the software recovery log, SYRIP:LOG; (or Survey)
• Test the alarm panel, ALLTI:ALI=ali;
• Print the external alarms, AXELP; and ALRDP;
• Print the digital path transmission functions quality data,
DTQUP:DIP=ALL;
• Print the CP error record, DIRCP;
• Print the RP event record, DIRRP:RP=ALL;
Record all events in the Exchange Journal and the applicable log.
QUARTERLY SUPERVISION
A quarterly supervision comprises such as Lifeline test (testing the
most important CP functions, initial starts, restarts, etc.), the
backup of IOG software and the backup of IOG exchange data and
RP load files.
PERIODIC SUPERVISION
A periodic supervision involves checking and testing, for example
ESD straps, HALON status, and the switch facility fire alarm.
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GSM BSC Operation
BLOCKING SUPERVISION
Blocking supervision informs operators that the number of blocked
RALT devices is too high. Different alarm classes can be specified,
depending on the number of blocked devices. The number of
blocked devices and alarm classes are set using the command
RABLC.
RABLC: Dety=
, lvb=
, acl=
;
Where:
Acl Alarm Class
Dety Device Type
Lvb
Limit Value Block
If the number of RALT devices is equal to or more than the
Blocking Level (parameter LVB) a blocking supervision alarm is
initiated. Before an alarm is initiated or prevented, the alarm
indication needs to take place twice above or below the defined
threshold. Measurements take place at an interval of 100 seconds –
see Figure 6-2.
The command RABLP is used to print out the supervision data for
the specified device types and RABLE is used to discontinue the
supervision. If the parameter PERM is added, the supervision is
removed permanently.
Application example of the blocking supervision:
RABLP: DETY=RALT;
This command prints out supervision data for specified device
types.
RABLC:DETY=RALT,LVB=30&60&90,ACL=A3;
See the definition of this command in first paragraph
RABLI:DETY=RALT;
The command connects/reconnects a device type to blocking
supervision.
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6 BSS Operations
*** ALARM 178 A1/APT "TIM TESTE"A 031106 1037
BLOCKING SUPERVISION OF DEVICE
DETY
LVB NDV BLO
RALT
90 1023 713
END
<RABLP:DETY=RALT;
BLOCKING SUPERVISION OF DEVICE DATA
DETY
LVB
ACL NDV ACTIVE
RALT
30 60 90 A3 1023 NO
END
Number of
blocked
devices
40
A1
30
A2
15
A3
ts
100 s
Alarm
Alarm increased
Alarm decreased
Figure 6-2. Alarm Printout/ Blocking Supervision
To maintain this alarm properly, the OPI Blocking Supervision of
Device should be used.
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GSM BSC Operation
SEIZURE SUPERVISION OF DEVICES
Seizure supervision of devices is implemented to monitor RALT
devices and to identify the equipment which is continuously busy
or not used during a specified time interval. Supervision can be
ordered per device type and Periodic Length (PL). PL specifies
the supervision period length (in hours). The RASSC command is
used to set up the supervision for specified devices. Seizure
supervision can be started and restarted with the command RASSI.
RASSC: dety=
, pl=
, acl=
;
Where:
Dety
Device Type
Pl
Supervision period length in hours.
ACL
Alarm Class
RASSI: dety=
;
Where:
Dety
Device Type
As illustrated in Figure 6-3, during the PL, RALT-36 is not seized
and RALT-40 is continuously busy. Therefore, these devices cause
the alarm SEIZURE SUPERVISION IN BSC. However, the
alarm does not indicate which of these devices is the cause of the
alarm. The RASAP command prints out the SEIZURE
SUPERVISION IN BSC ALARM OBJECTS. This report
provides information about the devices that have not been seized
and the devices continuously seized. Devices are indicated by name
and number. To prevent the alarm, the RASAR command must be
entered.
Application example of the seizure supervision of devices:
RASSC:DETY=RALT,PL=1,ACL=A1;
See the definition of this command in first paragraph
RASSI:DETY=RALT;
See the definition of this command in first paragraph
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6 BSS Operations
RASAR:DETY=RALT;
This command is used to order alarm reset of all unapproved
devices for specified device type with seizure supervision
active.
RASSE:DETY=RALT,PERM;
This command is used to disconnect seizure supervision of
devices per device type.
*** ALARM 183 A1/APT "TIM TESTE"A 031106 1143
SEIZURE SUPERVISION OF DEVICES IN BSC
DETY
RALT
END
RASAP;
SEIZURE SUPERVISION OF DEVICES IN BSC ALARMED DEVICES
CONGESTION IN DEVICE ALARM DATA LIST
NEVER USED DEVICES
DEV
STATE
RALT-1 IDLE
CONTINUOUSLY BUSY DEVICES
DEV
NONE
END
STATE
Figure 6-3. Alarm Printout
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GSM BSC Operation
RALT - 35
RALT - 36
RALT - 37
RALT - 38
RALT - 39
RALT - 40
Period Length (PL)
Figure 6-4. Seizure Supervision Initiated for RALT
To deactivate supervision, the command RASSE should be
entered. If the parameter PERM is added, supervision is
completely removed. If this is the case, the RASSC command with
the correct parameters must be entered again. The RASSP
command is used to order a printout of data for seizure supervision.
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6 BSS Operations
SEIZURE SUPERVISION OF LOGICAL CHANNELS
Seizure supervision of logical channels is implemented to monitor
TCHs and SDCCHs in order to identify equipment which is
continuously busy or not used during a specified time interval.
Supervision can be ordered for logical channels using the RLVLC
command. Parameter PL specifies the supervision period length.
(in hours).
Supervision can be started or restarted using the RLVLI command.
It is possible to specify in the command if the supervision is for
idle channels only, continuously busy channels only, or both.
RLVLC: chtype=
, pl=
, acl=
;
Where:
Chtype
Type of channel (TCH or SDCCH)
Pl
Supervision period length in hours
Acl
Alarm class
RLVLI: cell=
, chtype=
;
Where:
Cell
Cell designation
Chtype
Type of channel (TCH or SDCCH)
The alarm CELL LOGICAL CHANNELS SEIZURE
SUPERVISION does not indicate which logical channels caused
the alarm so the RLVAP command is used to provide a CELL
SEIZURE SUPERVISION OF LOGICAL CHANNELS
ALARM OBJECTS DATA printout. Here, logical channels not
seized and continuously seized are indicated by name and number.
To prevent the alarm, the RLVAR command must be used.
To deactivate supervision, the RLVLE command must be entered.
If the PERM parameter is added, supervision is completely
removed. In this case, the RLVLC command with parameters must
be entered again. The RLVLP command is used to order a printout
of data for seizure supervision.
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GSM BSC Operation
Application example of the seizure supervision of logical
channels:
RLVLP;
This command is used to order a printout of data for seizure
supervision of logical channels.
RLVLC:CHTYPE=TCH,PL=1,ACL=A1; - SETUP
See the definition of this command in first paragraph.
RLVLC:CHTYPE=SDCCH,PL=1,ACL=A1;
See the definition of this command in first paragraph
RLVLI: CELL=BTS021, CHTYPE=TCH;
RLVLI:CHTYPE=TCH;
THIS command format is used to connect a supervision on channel
type to one or several cells.
*** ALARM 184 A1/APT "TIM TESTE"A 031106 1304
CELL LOGICAL CHANNELS SEIZURE SUPERVISION
CHTYPE
TCH
END
RLVAP; - List channels
CHANNEL
CELL
STATE
TCH-8129
BTS021
IDLE
CONTINUOUSLY BUSY CHANNELS
CHANNEL
CELL
STATE
NONE
END
Figure 6-5. Seizure Supervision Of Logical Channels
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6 BSS Operations
SUPERVISION OF LOGICAL CHANNEL AVAILABILITY
Supervision of logical channel availability informs the operator if
traffic availability is too low on logical channels. In a cell, each
type of logical channel (TCH, SDCCH, BCCH or CBCH) is
checked against its alarm limit value. This limit value can be set by
command, or a default value can be used.
The supervision threshold is set using command RLSLC. The
parameter SCTYPE indicates the subcell type. This means that
different alarm levels in the overlaid and underlaid subcells can be
specified. In the overlaid cell, only CHTYPE = TCH or SDCCH is
possible.
RLSLC: cell=
spv=
;
, sctype=
, lva=
, acl=
, chtype=
,
Where:
Cell
Cell designation
Sctype
Channel Type (BCCH, SDCCH, CBCH and TCH)
Lva
Limit value for availability
Acl
Alarm class
Chtype
Type of channel (TCH or SDCCH)
Available
Channels
128
127
5
4
3
2
1
0
LVA
2.5 min
2.5 min
ts
30 s
Alarm
Alarm Ceasing
Figure 6-6. Supervision of Logical Channel Availability with LVA=4
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GSM BSC Operation
If the number of available logical channels is less than the defined
threshold, the alarm SUPERVISION OF LOGICAL
CHANNELS AVAILABILITY will be initiated. Each specified
channel type within the cell is checked every 30 seconds. If the
number of available channels is less than the preset alarm limit
value (LVA) in 2.5 minute intervals, an alarm occurs. If the number
of available channels is more than the LVA in a 2.5 minute interval,
the alarm ceases. If an alarm continuously occurs for the same cell,
the traffic load is too high and the number of channels should be
increased. See Figure 6-6 for this.
Supervision is started or restarted with the command RLSLI.
RLSLI: cell=
, sctype=
;
Where:
Cell
Cell designation
Sctype
Channel Type (BCCH, SDCCH, CBCH and TCH)
To maintain this alarm properly, the Cell Supervision of Logical
Channels Availability OPI should be used.
The RLSLP command is used to print out supervision data for
cells and the command RLSLE removes the alarm. If the
parameter PERM is added, supervision is completely removed.
Application example of the cell supervision of logical channels
RLSLP:CELL=BTS021;
This command prints out supervision of logical channels
availability data for the subcells of the specified cell(s) or the
subcells of all internal cells.
RLSLC:CELL=BTS021,CHTYPE=TCH,SPV=1,LVA=13,ACL=
A1;
See the definition of this command in first paragraph.
RLSLI:CELL=BTS021;
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6 BSS Operations
See the definition of this command in first paragraph
*** ALARM 181 A1/APT "TIM TESTE"A 031106 1138
CELL LOGICAL CHANNEL AVAILABILITY SUPERVISION
CELL
SCTYPE CHTYPE CHRATE SPV
BTS021
TCH
TCH
FR
FR
1
2
END
FIGURE 6-6 Alarm printout
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GSM BSC Operation
CALL PATH TRACING IN THE BSC
The Call Path Tracing function in the BSC is designed to provide
operations staff with a picture of a call connection through the
BSC. This function is initiated via the RAPTI command. One
command at a time is permitted from one terminal. The function is
free to be used again once the printout has started. Tracing can start
from a given device or a logical channel with a specified channel
type or Circuit Identity Code (CIC) as illustrated in Figure 6-6.
RAPTI: cic=
, or dev=
;
Where:
CIC
Circuit I dent it y Code ( CI C)
Dev
Type of device connect ed t o t he group swit ch
The CALL PATH TRACING IN BSC printout shows a picture of
the call connection including the devices linked together, the
switching data for established paths in the GS, and the used
channel. A printout is also provided for unstable connections, that
is, during setup, handover, or disconnection. The printout lists
branch links by branch if there are more than one.
The printout below shows links between software individuals
during a call where TCH-4095 is used. Once this information is
available, it is possible to continue tracing other individuals,
indicated in the printout.
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6 BSS Operations
R T T F 1D 118
R A L T 30
R T T F 1 D 1 122
R A L T 18
ETRALT
SPEECH
CODED
SPEECH
C 7S T 2 C 0
RHDEV 1
R B L T 1 02
LA PD
R B L T 98
G SS
Figure 6-7. Devices/Connections to Be Traced within the BSC
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GSM BSC Operation
<RAPTI:DEV=RALT-18;
CALL PATH TRACING IN BSC/TRC
LINK
MUP
SMUP
MUP
BRANCH-1
RALT-18
GS-0-122
GS-1-18
SMUP
BUSY
CIC-18
FID:H'00001D35
FID:H'00001D35
FID:H'00001D35
FID:H'00001D35
FID:H'00001D35
RTTPR-5680
RMCC-4547
RMHAIDL-4547
RABDI-4549
BRANCH-2
RTTPR-5680
RTTPH-179
RTPDI-179
RTTF1D1-122
RTTF1D1-118
BRANCH-3
RMCC-4547
RMHAIUL-4547
RABDI-4549
BRANCH-4
RMCC-4547
RMHBI-8147
TCH/F-8147
RCC-8113
RXCBM-1456
RXOTS-13-1-7
RXCDI-16240
RTTRINT-28
RBLT-98
FID:H'00001D35
FID:H'00001D35
GS-0-122
GS-0-118
6-7
GS-1-18
GS-4-98
BRANCH-6
TCH/F-8147
TCH/F-8147
BRANCH-7
RTTRINT-28
RTODCON-8178
BRANCH-8
RTTRINT-28
RTVPH-19385
RTAPH-49121
GS-4-98
2-3
GS-0-118
6-7
FID:H'00001D35
FID:H'00001D35
FID:H'00001D35
FID:H'0000DAD7
FID:H'0000DAD7
FID:H'0000DAD7
FID:H'0000DAD7
FID:H'0000DAD7
BUSY
FID:H'00001D35
DEBLOC
FID:H'0000DAD7
GS-4-257
GS-4-102
SEBU
GS-4-102
GS-4-257
SEBU
FID:H'00001D35
FID:H'00001D35
FID:H'0000DAD7
FID:H'0000DAD7
RXOIS-13
FID:H'0000DAD7
FID:H'0000DAD7
ABIS PATH DCP: 002
SPEECH/DATA DCP: 133
FID:H'0000DAD7
FID:H'0000DAD7
BRANCH-9
RHLAPD-3049
RXOLH-5075
RXOTRX-13-1
FID:H'0000DAD7
FID:H'0000DAD7
BRANCH-10
RXOLH-5075
RTTRINT-8
RTVPH-19450
RTAPH-49104
RXOIS-13
END
- 218 -
2-3
FID:H'00001D35
FID:H'00001D35
FID:H'00001D35
BRANCH-5
RMHBI-8147
LCSI-65232
RHLAPD-3049
RHDEV-1
ROSEMI-18430
RBLT-102
MISC
© Ericsson 2006
FID:H'0000DAD7
FID:H'0000DAD7
FID:H'0000DAD7
ABIS PATH DCP: 006
SIGNALLING DCP: 131
FID:H'0000DAD7
FID:H'0000DAD7
LZT 123 3801 R7A
6 BSS Operations
It is also possible to find the C7 signaling device that is used for the
MSC-BSC interconnection.
<RAPTI:DEV=RALT-30;
CALL PATH TRACING IN BSC/TRC
LINK
MUP
SMUP
MUP
SMUP
MISC
BRANCH-1
RALT-30
GS-9-30
GS-9-384
SECA-0
C7ST2C-0
GS-9-384
GS-9-30
SEBU
CIC-30
BRANCH-2
SECA-0
SECOM-0
END
Figure 6-8. RAPTI
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GSM BSC Operation
Intentionally Blank
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LZT 123 3801 R7A
7 BSC/TRC Maintenance
7 BSC/TRC Maintenance
Objectives:
Identify how to maintain BSC/TRC using the main
maintenance procedures described in the documentation.
ƒ Recognize the RBS Alarm Information displayed in the BSC.
Figure 7-1. Objectives
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GSM BSC Operation
Intentionally Blank
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© Ericsson 2006
LZT 123 3801 R7A
7 BSC/TRC Maintenance
BSC/TRC MAINTENANCE
GENERAL INFORMATION
System troubleshooting involves verifying the operational status of
the equipment, previously put into operation by the BSC/OSS
operator, using test commands to test the speech path between the
BTS and the BSC
FAULTS REPORTED FROM THE REMOTE TRANSCODER (TRA)
If the fault-suspected TRA board, R2 for example, contains only
one unit (for example one TRA Multiplexed (MUX) and four TRA
Demultiplexed (DEMUX) devices per TRA board), the TRA board
must be changed immediately because this TRA board cannot
handle any calls.
If the TRA board contains more than one unit and a unit is faultsuspected, the TRA board may still be capable of handling calls. A
decision is then made whether or not to change the TRA board
immediately or to wait, for example, until low traffic hours.
If a Partial Board Fault is reported the TRA board is still capable of
handling calls, and therefore a decision is made as to whether to
change the TRA board immediately or to wait for low traffic.
RADIO TRANSMISSION TRANSCODER AND RATE ADAPTOR FAULT
SNT
CARD
DEV
REASON
snt
card
dev
reason
END
Figure 7-2. TRA Fault Printout
Maintenance of TRA Equipment
Commands are provided for blocking and deblocking.. TRAs
which have been seized cannot be manually blocked without using
the FORCE parameter. All deblocked devices are continuously
supervised for hardware faults, regardless of whether they are
seized or not. Supervision of loss of synchronization is only
performed for seized, deblocked devices. Routine tests are
performed at a predefined interval for all idle TRAs.
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GSM BSC Operation
Each DEMUX carrying traffic synchronizes to its corresponding
time slot function in the BTS. Loss of synchronization is reported
to the BTS that in turn notifies the BSC. V110 synchronization is
available for statistical purposes for some TRA versions.
A specific transcoder equipment alarm –see Figure 7-2, will be
generated when one of these faults is reported:
•
•
Routine testing detects a fault
•
GS clock supervision error
•
TRAB not operational
Transcoder channel fault
Faults concerning a larger part of an SNT or an entire SNT will be
taken care of by the SNT Administration function.
A fault in seized TRA equipment leads to an automatic blocking of
the faulty equipment and a change to faultless equipment, if
available.
PROGRAM LOADING OF TRA-EMS
This provides the operator with the function to initiate program
loading of loadable Transcoder Rate Adapter Boards (TRABs).
The function can be used to carry out function updates, to correct
faulty software units, and for program loading after hardware
repair.
Initiation of Program Loading
The Device Software Unit (DSU) is uniquely identified in the
operator commands by the Software Unit Identity (SUID). The
Software Unit NAME (SUNAME) can also be used, but it is not
necessarily unique. The loading of a DSU from the Central
Processor Program Store (CP-PS) into one or more TRA-EMs is
initiated by command.
The loading can be either conditional or unconditional. If loading is
conditional, the DSU loaded on the TRA-EMs is compared to the
DSU in CP-PS. Loading will not be initiated if the DSU is already
loaded in the TRA-EM. With unconditional loading, previously
loaded software will be overwritten.
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© Ericsson 2006
LZT 123 3801 R7A
7 BSC/TRC Maintenance
Program loading can only be ordered for manually blocked SNTs.
The TRA-EMs must be deblocked before downloading is initiated.
Traffic remains in the rest of the system except when TRA R3 is
loaded. The TRA-EMs belonging to the same RP, must be blocked
so as not to overload the RP. TRA R2 is not loadable.
Termination of Program Loading
Program Loading of TRA-EMs ordered by command, but not yet
started, can be terminated by command. The command can be
given for specified TRA-Ems, or for all TRA-EMs. The loads in
progress will be completed. Loads that have been completed will
not be affected.
Commands summary that should be used to load the software DSU in
the units TRAU
Part of the Operational Instruction describes the procedure to load a
Device Software Unit (DSU) from the Central Processor-Program
Store (CP-PS) into the Transcoder and Rate Adaptor-Extension
Modules (TRA-EMs). The operator can use the TRA-EM loading
function to perform function updates, program corrections and
program loading after hardware repair actions.
The following conditions must apply before this procedure can be
completed:
•
•
A work order has been received indicating that a DSU is to be
added, removed or replaced.
When a DSU is to be added or replaced an external storage
medium holding the DSU must be available (the volume and
file identity must be known by the Input/Output (IO) system).
1. Prepare the external storage medium.
2. Connect the volume to the IO device.
This Operational Instruction describes the procedure to define a file
on a Hard Disk (HD) in a Support Processor Group (SPG). The
function is implemented in the File Management Subsystem
(FMS).
I N M CT
This command initiates the use of file management commands in
the specified support processor group
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GSM BSC Operation
I N FI I
This command creates keyed files and subfiles in a Support
Processor (SP).
En d;
Initiating DSU's Load
1 Initiate loading of the DSU from an external medium to CP-PS
LAEUL
Command LAEUL initiates loading of specified RSUs from a file
device to the Central Processor (CP) memory.
2 Define the TRA-EM and link the equipment to the SNT owning
software unit
EXEM I
This command is used for defining an EM and for linking
equipment to a software unit. The command may be given to both
blocked and deblocked non-loadable RPs with program pages.
3 Connect the SNT to the Group Switch
N TCOI
This command connects an SNT to a Group Switch (GS), a
Subscriber Switch (SS), or an External Switch.
4 Manually deblock the SNT to which the transcoder belongs
NTBLE
This command deblocks an SNT or a subordinate SNT. When an
SNT with subordinate SNTs is specified in the command, only the
specified subordinate SNTs are deblocked. Otherwise, the complete
SNT is deblocked.
5 Connect the TRA devices to the SNT
EXD UI
This command connects devices to a switching network terminal
unit.
6 Bring the TRA devices into service.
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7 BSC/TRC Maintenance
EXD AI
Command EXDAI brings a device into service from a PRE-POST
SERVICE state. It will not be allowed to bring RBLT devices into
service in a stand-alone Transcoder Controller (TRC) and
Transcoder devices into service when the node type is stand-alone
Base Station Controller (BSC).
7 Deblock the TRA devices
RRTBE
This command deblocks all the specified transcoder Multiplexed
(MUX) devices and their associated Transcoder Demultiplexed
(DEMUX) devices.
8 Connect blocking supervision. Use parameter DETY=dety
RABLI
The command connects/reconnects a device type to blocking
supervision.
9 Initiate tying of DSUs to the SNT owning blocks
EXD TI
Command EXDTI ties a specified device software unit to the
specified application block or equipment.
10 Initiate loading of the DSU from the CP-PS into the TRA-EMs
RRD SL
The command is used to load a DSU from the Central ProcessorProgram Store (CP-PS) into TRA-EMs.
11 Initiate a printout of information about DSU associated with
SNTs
RRD SP
The command is used to initiate an answer printout of device
program information for transcoder SNT(s).
cf
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GSM BSC Operation
Operational Instructions
Administration of Program Loading of TRA-EMs
Program Loading of TRA-EMs, Abort
Program Loading of TRA-EMs, Initiate
Radio Transmission Transcoder and Rate Adapter To SNT,
Connect
Radio Transmission, Transcoder and Rate Adapter From SNT,
Disconnect
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© Ericsson 2006
LZT 123 3801 R7A
7 BSC/TRC Maintenance
SRS MAINTENANCE
FAULT DETECTION
Faults are detected by supervision of the hardware. The supervision
process begins when the unit is in an operational state (deblocked).
Upon detection of a possible fault, a process of fault localization
and isolation begins. Fault detection is performed by:
• Continuous supervision: The hardware is continuously
monitored to detect erroneous behavior. Deviations from the
expected faultless behavior are detected as disturbances.
•
•
•
•
Routine test: The continuous supervision is tested periodically
to ensure that it can detect erroneous behaviors correctly.
Deviations from the expected fault rate are detected as
disturbances. Routine tests do not disturb traffic.
Disturbance recording: All disturbances, recorded by routine
tests and continuous supervision, are recorded.
Disturbance filtration: A fault exists when the disturbance
rate for a specific fault type reaches a defined value. The
definition of the value is related to the frequency and duration
of the disturbance.
Fault indication: When a fault is detected by the continuous
supervision or in a routine test, the fault indication is sent to the
fault localization process. The fault indication consists of
information identifying the fault type and fault position.
FAULT LOCALIZATION
If several fault indications are received due to fault propagation,
only the originating fault is localized. If many independent faults
are indicated in the hardware simultaneously, they will be localized
as separate faults. When a fault has been localized, the supervision
is stopped on the affected hardware component, leaving the
supervision active on the faultless part.
Fault localization is also performed on the interfacing hardware
components that are affected by the localized fault. This is done to
avoid unnecessary maintenance work.
When the fault localization is concluded, the fault indication is sent
to both the intermittent fault detection process and the alarm
handling process.
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GSM BSC Operation
INTERMITTENT FAULT DETECTION
The aim of this process is to determine if a localized fault can be
restored. If a fault has been restored three times within a specified
time period without success, it will be treated as a permanent fault.
Restoration attempts are stopped and a manual intervention is
necessary to restore the unit to service.
RESTORATION
The aim of this process is to test if the SRS unit can be brought
back into service. It cannot be put into service if the localized fault
remains. The restoration function uses the supervision to check for
a faultless situation.
If an intermittent fault has not occurred, a restoration attempt is
made in the restoration process. If restoration is successful, no
more attempts are made. The disturbance counter for the fault has
gone down to a value where the hardware can be considered
faultless. Fault localization on the affected part of the hardware is
stopped.
Permanence of a fault situation is determined when restoration has
failed a number of times. Then manual intervention is necessary.
Restoration is not performed if the SRS unit is manually.
ALARM HANDLING
The aim of this process is to receive the alarm indications from the
autonomous maintenance function and to make the operator aware
of them. The alarm types are:
•
•
ALARM FOR FAULT
Given with an indication of the board, based on the results from
the fault localization process. A maximum of two boards are
indicated in the printout. They are listed in order of probability,
fault origin.
ALARM FOR MANUAL BLOCKING
The alarm is issued when the SRS unit is manually blocked. It
is ceased when the unit is manually deblocked.
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© Ericsson 2006
LZT 123 3801 R7A
7 BSC/TRC Maintenance
SRS CONGESTION SUPERVISION
The failure rate experienced by users requesting Subrate paths to be
setup through the group switch is continuously supervised to detect
congestion in the SRS.
Data is continuously read from counters recording connection
information about incoming and outgoing MUPs towards the
Group Switch and sub-MUPs within the SRS. At a pre-defined
alarm interval, the failure rate is evaluated and the alarm situation
is updated. This can involve either raising a new alarm, changing
the alarm class of an existing alarm or ceasing the alarm. The alarm
level is set in the parameter list, default value five minutes.
It should be noted that the congestions and faults that are counted
can originate from both the traditional group switch and the subrate
switch. It is only active when using the TST based group switch.
ALARM HANDLING
The Alarm generated for congestion in SRS is indicated in Fig 7.3.
If the alarm is received in a TRC/BSC Node, the OPI HIGH
FAILURE RATE IN SUBRATE SWITCH SUPERVISION is used.
This OPI directs the BSC/OSS operator to check for GSS related
faults and/or check that SRS dimensioning is appropriate for the
traffic levels in the BSC/TRC.
HIGH FAILURE RATE IN SUBRATE SWITCH SUPERVISION
FAILURES
CONGESTIONS
FAULTS
failures
congestions
faults
END
Figure 7-3. Failure Supervision Alarm
MANUAL BLOCKING OF AN SRS UNIT
If the blocking is successful, the supervision is stopped and an
alarm is issued to show that the unit is blocked. If there is an alarm
indicating a fault, previously raised for this SRS, the alarm is
ceased. A printout is issued to indicate the blocking result.
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GSM BSC Operation
MANUAL DEBLOCKING OF AN SRS UNIT
The manual blocking alarm for the SRS is ceased. A test is carried
out to check if the SRS is faultless. If the test is successful, the
supervision is activated and the SRS is operational. Otherwise, a
fault alarm will be issued and the SRS is auto-blocked. A printout
is issued to indicate the deblocking result.
AUTOMATIC BLOCKING/DEBLOCKING OF AN SRS UNIT
Autoblocking of an SRS occurs on detection and on completion of
the fault localization. Autodeblocking removes the automatic
blocking of the SRS upon successful restoration.
EM BLOCKING/DEBLOCKING
Upon EM blocking, all restoration tests or fault alarms are ceased.
If both SRS planes have been EM blocked, the SRS reserves call
connection release.
If the first EM from the CM is deblocked, a repeated calling of the
EM starts. If the unit is not blocked the supervision is started. The
SRS is tested as well as the SRS-GS interface.
EM RESTART
EM restart is requested of the SRS by APZ. SRS orders the start of
repeated calling of the EM. Traffic connections are updated. Note
that the EM restart will not proceed if both planes are EM-blocked.
TESTING AN SRS UNIT
Test of an SRS unit can be ordered for the following:
•
•
•
•
•
- 232 -
Manual test via the command NTTEI:SNT=SRS-n;
Checks both planes of the SRS unit.
Test at localization: Part of fault localization. Checks only the
localized plane.
Test at restoration: Initiated by the RP at the restoration of the
unit. Checks only the localized plane.
Test at manual deblocking: Initiated by command and includes
a test of both planes.
Routine test: Each plane is tested separately.
© Ericsson 2006
LZT 123 3801 R7A
7 BSC/TRC Maintenance
COMMAND ORDERED LOOP TEST
This feature makes it possible for the BSC/OSS operator to order a
test of the connections between the BSC and a transceiver function
in a BTS. This feature orders a loop to be set up between the BSC
and the TS in the BTS – see Figute 7-4. A test pattern is passed
through the loop. If the test pattern is returned within a preset time,
a correct connection is assumed to exist. The TS should have been
taken into service and should be manually blocked. The resulting
printout indicates if the connection was correctly set up. If it is
impossible to perform the test, the test results indicate the reason.
The command is:
RXLTI:MO=RXOTS-2-0-0;
RADIO X-CEIVER ADMINISTRATION
TRC-BTS LOOP TEST RESULT
MO
RESULT
RXOTS-2-0-0
TEST SUCCESSFUL
TRADEV
TRCATERDEV
BSCATERDEV
RTTF1D2-8
ABISDEV
RBLT-77
END
. Figure 7-4. Example of a Loop Test Printout
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GSM BSC Operation
Intentionally Blank
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© Ericsson 2006
LZT 123 3801 R7A
BTS Maintenance
8 BTS Maintenance
Objectives:
Execute BTS maintenance based on node diagnosis of fault
conditions using the on-line documentation and
maintenance procedures.
Figure 8-1. Objectives
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GSM BSC Operation
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© Ericsson 2006
LZT 123 3801 R7A
BTS Maintenance
BTS MAINTENANCE
GENERAL INFORMATION
During normal network operation, the BSC performs supervision
of its own software; all connected BTSs and the signaling and
transmission network. In addition, each BTS performs supervision
of internal equipment, internal software, and the connected
equipment.
Supervision assures that faults or abnormal conditions in the
network are detected and reported to the BSC. An alarm in the BSC
informs the user of a detected fault..
ALARM HANDLING AND DESCRIPTIONS
Faults occurring in the BTS which permanently affect the normal
operation of the equipment, will be detected by BTS software and
are reported to the alarm handling block in the BSC. The event is
stored in two separate event registers, the faulty unit list, and the
error log, and is automatically printed out by the alarm printer as
shown in Figure 8-2. If the alarm is not automatically printed the
command ALLIP can be used to check different active alarms in a
BSC.
A3/SW-DEV "R8A2A13_21225_0" 060 000317
RADIO X-CEIVER ADMINISTRATION
MANAGED OBJECT FAULT
MO
RXOTRX-2-4
1230
RSITE
MALDON3
ALARM SLOGAN
BTS INTERNAL
Figure 8-2. Example of an Alarm Printout
The command RXASP (Figure 8-3) can be used to print all TG
(RBS) with faults in the BSC. This command is useful in the O&M
process to help the operator to identify all TG with alarm and after
this the command RXMFP can be used for more details (Figure 84).
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GSM BSC Operation
RXASP:moty=rxotg;
RADIO X-CEIVER ADMINISTRATION
MANAGED OBJECT ALARM SITUATIONS
MO
RXOCF-2
RXOTRX-2-5
RXOTRX-2-8
RXOTRX-2-9
RXOCF-3
RXOCF-4
RXOTRX-4-4
RXOTRX-4-5
RXOTS-4-2-4
RXOTS-4-2-5
RSITE
2206
2206
2206
2206
2106
2102
2102
2102
2102
2102
ALARM SITUATION
BTS INT UNAFFECTED
BTS INT UNAFFECTED
OML FAULT
OML FAULT
BTS INT UNAFFECTED
BTS INT UNAFFECTED
OML FAULT
OML FAULT
TS SYNC FAULT
TS SYNC FAULT
Figure 8-3. Example of TG Faulty Printout
RXMFP:MO=RXOTG-2,FAULTY,SUBORD;
RADIO X-CEIVER ADMINISTRATION
MANAGED OBJECT FAULT INFORMATION
MO
RXOCF-2
RU
0
BTSSWVER
ERA-G03-R03V0
RUREVISION
BOE 602 14/1
.
.
.
STATE
OPER
BLSTATE
INTERCNT
00002
RUSERIALNO
X510009569
R5B
.
.
.
CONCNT
CONERRCNT
LASTFLT
LFREASON
FAULT CODES CLASS 2A
30
REPLACEMENT UNITS
3
Figure 8-4. Example of a Faulty Printout
The faulty unit list comprises information on all equipment that has
been taken out of service due to active alarms, while the error log
comprises historical information on active and previous alarm
events. The stored information can be retrieved by the commands
RXELP (Figure 8-5).
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© Ericsson 2006
LZT 123 3801 R7A
BTS Maintenance
<RXELP:MO=RXOTG-2;
RADIO X-CEIVER ADMINISTRATION
ERROR LOG DATA
FAULT INFORMATION LOG
MO
RXOCF-2
BTSSWVER
ERA-G03-R03V0
DATE
06-03-13
TIME
15-38-06
BTS
STA
REPLMAP
000000000000 000000000008
1AMAP
000000000000 000000000000
1BMAP
000000000000 000000000000
2AMAP
000000000000 000040000000
EXT1BMAP
0000
EXT2BMAP
0000
Figure 8-5. Example of an Error Log Printout
When a BTS alarm is issued, the BSC operator determines if the
fault is permanent by performing a test on the faulty equipment.
The OPI Radio X-ceiver Administration Managed Object Fault
should be used as a first step to locate the source of the fault.
1. Compare the fault indication to the recorded information in the
error log. If a specific fault has occurred previously in the same
BTS, it might be a hardware fault. If the fault occurs throughout
the system and no particular HW fault is found, a trouble report
should be issued.
RXELP:MO=mo
2. Print MO faults information.
RXMFP:MO=mo
3. Manually block the faulty equipment.
RXBLI:MO=mo
4. Test the faulty MO.
RXTEI:MO=mo
If the test indicates a fault in the MO, the MO should be repaired
according to the fault code list in the O&M manual for the BTS.
The test result should be used as an input for the fault analysis.
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GSM BSC Operation
5. If the test does not indicate any faults, the MO can be
deblocked.
RXBLE:MO=mo
If the alarm is serious, it is reported as a class 1 alarm and
immediate action should be taken to isolate the faulty unit. The
BSC initiates a test to verify the fault and locate the Regional Units
(RUs). If the alarm is not serious, it is reported as a class 2 alarm.
When the alarm is deactivated, it is documented on an alarm stop
printout.
FAULT DESCRIPTION
The functionality dedicated to detect faults in an MO is called
Supervision. Each MO is responsible for its own supervision. Fault
reports may be preceded by a fault filtering function of the detected
disturbance. The filtering can, for example, be an averaging
function or a disturbance counter. The output from the fault filter
has a normal range where a specific fault type is not activated.
When this limit is passed, the fault becomes active. This means a
fault report is sent to the BSC. There is a fault map for each class
of BTS internal faults, each map containing 48 bits. This provides
the opportunity to detect up to 48 different faults of each class
within any object. If the disturbances that caused the fault report
disappear or become less frequent, the output from the fault filter
may pass into the normal range again. For some faults, where a
fault cease condition is defined, information about the fault ceasing
is sent to the BSC.
For some fault types, the cause of the disturbance disappears when
the MO is disabled. Therefore, these fault types are latched, that is,
no possible fault stop conditions exist until the procedure is
executed and terminated. The only way to stop a latched fault is to
block and deblock the equipment using the commands RXBLI and
RXBLE.
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BTS Maintenance
DISTURBANCE DESCRIPTION
The disturbance sources in the BTS comprise a number of
internally supervised test points. The test points can be a
component, an equipment part, or a physical parameter. When the
supervision detects that a predefined limit for normal operation has
been exceeded during a predefined time interval, a disturbance has
occurred. Disturbances are fed through a fault filtering mechanism
to the fault detectors. Each fault detector controls an individual
fault state bit within the fault map. The fault filtering mechanism is
a classification algorithm for disturbances. A fault is issued in these
cases; a single disturbance may be sufficient, due to its seriousness,
or several disturbances over a certain time interval are necessary.
All faults do not have a specific disturbance identity.
FAULT AND REPLACEMENT UNIT MAPS
When a fault is reported in the BSC, the report includes
information about the most probable RU where the fault may be
located. In some cases several possible RUs may be identified.
Decoding of Fault Maps: All fault and RU codes consist of a
number of hexadecimal digits, mostly twenty four. These twenty
four digits represent a map consisting of 96 bits. Each bit
represents a decimal number and can be translated into a
description using the fault class and RU maps. An exception is the
code for an external fault. This code contains only four
hexadecimal digits (16 bits). The decoding principle –see Figure 86, is the same as for the twenty four- digit-code.
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Fault Code 0.…0 0 0 0 0 2 8 0 0 0
95 - 92
...... 39 - 36 35 - 32 31 - 28 27 - 24 23 - 20 19 - 16 15 - 12 11 - 8
7-4
3-0
0
0
95 - 92 ……. 39 - 36 35 - 32 31 - 28 27 - 24 23 - 20 19 - 16 15 - 12 11 - 8 7 - 4
3-0
0
0
0
0
0
0
2
8
0
Hexadecimal to Binary Conversion
0
0000
0
0000
0
0000
0
0000
0
0000
19 18 17 16
0 0 1 0
Bit 17 Active
0
0000
2
0010
8
1000
0
0000
0
0000
0
0000
15 14 13 12
1 0 0 0
Bit 15 Active
Figure 8-6. Conversion Process
ERROR LOG
The error log is a memory area in the BSC used for storing fault
information, received from a BTS. The error log contains
information, received in the BTS Fault Reports and also
information about when the different reports were received. The
information provided per entry in the error log printout includes:
MO, MO class, the entry date, and the time the entry was made.
BTS STATE
The BTS state shows the last known state of the MO in the BTS.
POSSIBLES BTS states are:
RES
STA
DIS
ENA
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RESet
STArted
DISabled
ENAbled
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BTS ALARM COORDINATION
The alarm management costs for a network are reduced. This is
achieved by reducing the number of alarms, reported in the BSC
without reducing the available information on reported faults.
FAULT REPORTING
Faults and the resulting alarms are reported on Managed Objects
(MO) rather than on the equipment. Thus, faults in BTS equipment
are reported on the MO representing that equipment. Faults
reported on the signaling and transmission network are reported on
the supervising MO. Using the MO assures a consistent reporting
interface for a network comprising a variety of product types.
FAULT ANALYSIS
Faults detected in the network are analyzed and grouped according
to origin and effect. An alarm may be issued to indicate a number
of faults with the same origin and effect, such as secondary faults.
This reduces the number of alarms. When the user responds to an
alarm, information on all reported faults may still be obtained.
ALARM CLASSIFICATION
Alarms are classified according to user importance. Faults affecting
traffic capability and other essential functions are reported by a
high priority alarm. This makes it possible to identify and address
the faults promptly. Faults indicating transient or abnormal
conditions, not affecting the traffic capability, are reported by a
lower priority alarm.
ALARM COORDINATION
Alarms are coordinated according to priority. Coordination reduces
the number of alarms reported in the BSC. Coordination may be
performed at the Managed Object (MO) or Transceiver Group (TG)
level. The user may set the alarm coordination level for all TGs
connected to a BSC, or for an individual TG.
When alarm coordination is at the MO level, an alarm is issued for
the highest priority fault, present on an MO. A number of alarms
may be issued for a TG if there are other faults besides those in the
MO. When the user responds to an alarm, information on all the
reported faults for the MO may be obtained.
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When the alarm coordination is at the TG level, one alarm is issued
for the highest priority fault present within a TG. Several alarms
may be issued in the BSC in case there are faults in more than one
connected TG. When the user responds to an alarm, information on
all the reported faults for the TG may be obtained.
SPECIAL ADJUSTMENTS
A number of special adjustments may be made to BTS Alarm
Coordination. This enables users to adjust the Alarm management
process according to their own working procedures. Alarm
masking enables users to suppress specified alarms altogether.
Thus, no alarm is issued either for a group of faults (by origin and
effect), or for individual faults. Information on all the reported
faults is still available. Each alarm is issued with an Ericsson
defined default priority. The user may specify a different priority
for one or more alarms. If an alarm is masked the new priority is
retained. Thus, if the alarm is subsequently unmasked the new
priority is still applicable. Each fault, reported by the BTS, may
result in an alarm.
INCREASED IN SERVICE PERFORMANCE
Faults affecting the traffic capability and other essential functions
are reported by an alarm of the highest priority. When present,
these alarms take precedence over and suppress the issuing of
lower priority alarms. The user can increase or decrease the priority
of the alarm that is issued. The user can suppress the issuing of
specified alarms altogether. Therefore, faults of no importance need
not be responded to.
FAULT CLASSIFICATION
Faults are classified according to origin and priority. The origin
indicates whether the fault is found in the BSC (internal to the
BTS), in equipment connected to the BTS, or in the signaling and
transmission network. The priority indicates to what degree the
traffic capability or other essential functions are adversely affected.
Most faults can be automatically remedied. In that case, no alarm is
issued. Some faults indicate a transient abnormal condition. A low
priority alarm may be issued for these. Some faults indicate that
some type of user intervention is required (for example,
replacement of equipment). A high priority alarm is issued in these
cases.
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ALGORITHM
The BTS Alarm Coordination determines the alarm situation for an
MO or a TG. It is preferable to have a good knowledge of the
algorithm described in Figure 8-5 before making the adjustments.
Start
A • A new alarm class overrides the default class for the alarm
Leave Alarm
Coordination
Determine all
conditions
situation / BTS condition
• Any BTS condition present in either 'Internal Class 1A' or
'Internal Class 1B' fault map has alarm situation 'BTS
INTERNAL (MO AFFECTED)'.
• Any BTS condition present in 'Internal Class 2A' fault map
has alarm situation 'BTS INTERNAL (MO
UNAFFECTED)'.
• Any BTS condition present in 'External Class 1' fault map
(but excluding those with a specific alarm situation) has
alarm situation 'BTS EXTERNAL (MO AFFECTED)'.
• Any BTS condition present in 'External Class 2' fault map
(but excluding those with a specific alarm situation) has
alarm situation 'BTS EXTERNAL (MO UNAFFECTED)'.
• Several BTS conditions have specific alarm situations
associated with them. These are the following conditions
reported in 'External Class 1' fault map: 'Local/Remote
Switch', 'LMT', 'LAPD Queue Congestion' and 'TRA/PCU
Sync Fault' and the following conditions reported in
'External Class 2' fault map: 'Mains Failure' and 'RBS Door'.
Is
a specific
Yes
BTS condition
masked
No
•Note: If the user has specified a new alarm class for any of
these BTS conditions, this overrides the default alarm classes.
Refer to
Table 1
Obtain the
alarm
situation and
default alarm
classes
Leave Alarm
Coordination
B
a specific
alarm situation
masked
• If TG Alarm Coordination is at the MO level an alarm
is issued for the highest priority alarm situation present for
the MO. BTS Alarm Coordination is complete.
No
• If TG Alarm Coordination is at the TG level the highest
priority alarm situation present in the TG is determined.
• If there is more than one alarm situation present of the
highest priority alarm class, they are prioritized
according to an Ericsson defined sequence. An alarm
situation of the highest priority is thus obtained for the TG.
new alarm cl.
or BTS condition
defined
Yes
&B
Refer to
Table 1
• Determine the alarm situation(s) present on the TG and
subordinate the MO with the highest priority alarm class.
Is a
A
• If there is more than one alarm situation present with the
highest priority alarm class, they are prioritized
according to an Ericsson defined sequence. One alarm
situation of the highest priority is thus obtained for the
MO.
Is
Yes
• Determine the alarm situation(s) present with the highest
priority alarm class. Alarm situations are prioritized by
alarm class in the order A1 > A2 > A3 > O1 > O2.
No
• An alarm is issued for the highest priority alarm
situation present for the TG.
B
BTS Alarm Coordination is complete.
Figure 8-7. 8Alarm Coordination Algorithm
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CONDITIONS AND ALARM SITUATIONS
Table 8-1 states all conditions with an associated alarm situation.
BTS
Condition
Priority
Alarm Situation
TGC Fault
1
TGC FAULT
Permanent Fault
2
PERMANENT FAULT
Local/Remote Switch (External Class 1)
3
LOCAL MODE
LMT (External Class 1)
4
LMT INTERVENTION
Loop Test Failed
5
LOOP TEST FAILED
All Internal Class 1
6
BTS INTERNAL (MO AFFECTED)
Mains Failure (External Class 2)
Other External Class 1
7
MAINS FAILURE
8
BTS EXTERNAL (MO AFFECTED)
OML Fault
9
OML FAULT
Abis Path Unavailable
LAPD Queue Congestion (External Class 1)
10
ABIS PATH UNAVAILABLE
11
CON QUEUE CONGESTION
TRA/PCU Sync fault (External Class 1)
12
TS SYNC FAULT
All Internal Class 2
13
BTS INTERNAL (MO UNAFFECTED)
Other External Class 2
14
BTS EXTERNAL (MO UNAFFECTED
Forlopp Release
15
FORLOPP RELEASE
RBS Door Open (External Class 2)
16
OPERATOR CONDITION
Def. Al
Class
A2
A2
A2
A2
A2
A2
A2
A2
A2
A2
A2
A2
A3
A3
A3
O1
Table 8-2. Conditions and Alarm Situations
When a condition is qualified as (External Class 1) or (External
Class 2) it indicates that the condition is reported in 'External Class
1' or 'External Class 2' fault maps, respectively, having a specific
associated alarm situation. The designation 'Other External Class 1'
indicates all conditions reported in 'External Class 1' fault map
excluding the conditions 'Local/Remote Switch', 'LMT', 'LAPD
Queue Congestion', and 'TRA/PCU Sync Fault'. The designation
'Other External Class 2' indicates all conditions reported in
'External Class 2' fault map excluding the conditions 'Mains
Failure' and 'RBS Door Open'.
Origin indicates where the condition is detected. An origin of 'BSC'
indicates that the fault is supervised for and detected in the BSC.
An origin of 'BTS' indicates the fault is supervised for and detected
in the BTS and reported to the BSC.
The Alarm Class indicates the Ericsson defined default alarm class
for each alarm situation.
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ALARM PRIORITY RESOLUTION
Table 8.1 also indicates how alarm situations are prioritized when
more than one alarm situation of the same alarm class is present for
an MO. The table is ordered by priority from 1 (highest) to 16
(lowest). The highest priority alarm situation present suppresses
any alarm situations of lower priority. For example, if 'LOCAL
MODE' and 'MAINS FAILURE' are present and belong to the
same alarm class, the resulting alarm situation is 'LOCAL MODE'.
In addition, the table indicates the alarm slogan that is output for a
given alarm situation.
The alarm slogan is the description of the current alarm situation
for an MO or a TG. The alarm slogans 'BTS INTERNAL' and 'BTS
EXTERNAL' describe more than one alarm situation. The
remaining alarm slogans describe a unique alarm situation. This
section describes how each alarm slogan should be interpreted.
TGC FAULT No active TGC application exists in the Transceiver
Group.
PERMANENT FAULT A managed object is classified as
permanently faulty when fault situations have occurred, and have
been attended to a certain number of times, within a certain
timeperiod. Manual intervention is required to bring such
equipment back into operation.
LOCAL MODE The BTS equipment is in Local Mode, or the
BTS equipment has changed from Local to Remote Mode and a
fault exists in the communication link between the BSC and the
BTS. Communication between the BSC and the BTS is not
possible.
LMT INTERVENTION Local maintenance activities are
performed in the BTS.
LOOP TEST FAILED A test of the traffic carrying capabilities of
the TS has failed.
BTS INTERNAL There is a fault internal to the BTS.
MAINS FAILURE There is a fault in the power supply to the BTS
or in one or several equipment components within the BTS. Battery
backup (if available) is in use. Escalation may occur if corrective
action is not taken.
BTS EXTERNAL There is a fault external to the BTS.
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OML FAULT There is a fault in the communications link between
the BSC and the BTS.
ABIS PATH UNAVAILABLE No transmission device exists
between the BSC and the BTS.
CON QUEUE CONGESTION At least one of the LAPD
Concentrator concentration outlet queues has reached an
unacceptable filling level.
TS SYNC FAULT Synchronization lost on up-link or down-link
TRA or PCU channels.
FORLOPP RELEASE A fault has occurred within the BSC
Software leading to a Forlopp release. Automatic recovery
procedures will take place. Report to your Ericsson Support Office.
Alternatively, this alarm is issued as an advisory hint following a
command ordered Forlopp release of a TG. In either case, the alarm
is automatically ceased after successful recovery.
OPERATOR CONDITION A fault condition has arisen due to
operator intervention.
BTS LINK FAULTS
Disturbances affecting Operation and Maintenance Link (OML)
or Radio Signaling Link (RSL) links are reported to the Handling
of BTS Related Faults function. There are three types of links
affected by disturbances:
OML-TC
The link to the TRU. One link per TRU.
OML-TGC
The link to the active TGC application. One link
per TG.
RSL
The link to the TCHs. One link per TRU.
For each link type, there are four types of reports:
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Disturbed
Indicates that there is something wrong with the
link and another report will soon follow.
OK
Link, previously reported disturbed or faulty,
has now recovered. Communication is restored.
Change
Not possible to recover link, previously reported
disturbed. However, a spare signaling device
was used as a replacement. Communication is
restored.
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Fault
Link is not usable.
Table 8-2 summarizes actions taken, depending on link type and
report type.
OML-TC
OML-TGC
RSL-TRXC
Disturb
ignore
ignore
5
OK1
ignore
ignore
7
OK2
1
3
4
Change 1
ignore
ignore
7
Change 2
1
3
4
Fault
2
3
6
Report Type
Table 8-3. Maintenance Link
Key to Table
OK1
OK2
Change1
Change2
1
2
3
4
5
6
7
When Link OK occurs after Link Disturbed.
When Link OK occurs after Link Fault.
When Link Change occurs after Link Disturbed.
When Link Change occurs after Link Fault.
Bring affected MOs automatically back into
operation.
Take affected MOs out of operation.
Inform TGC Handling.
Any associated BPCs can be made available for
traffic.
Block BPCs without forced release.
Block BPCs with forced release.
Deblock BPCs.
SYSTEM INTERNAL FAULTS
A system internal fault occurs when the BSC identifies an MO
operating in an abnormal way, for example, a message to the BTS
times out without receiving a reply. When such a fault occurs, the
function waits for a certain time and then an attempt is made at
discovering the cause. During this period, the MO is taken out of
operation. If no cause is discovered, the MO resets, and it is
conditionally loaded and tested, and its BTS parameters are
updated when brought back into operation.
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BRINGING MOs INTO OPERATION
The actions described in the sections below are involved when
bringing an MO back into operation.
CHECK FOR TOO MANY FAULTS
These faults can be faults affecting functionality, reported by the
BTS; LMT Intervention, Spontaneous MO Reset, or System
Internal Faults. MOs reporting more than a specified number of
such faults during a given time are called unstable objects.
Unstable MOs will be permanently taken out of operation,
preventing possible traffic disturbance. Manual blocking and
deblocking are required to bring the MO back into operation.
A Leaky Bucket algorithm is used to calculate when an MO is
permanently faulty. Each MO Class has a threshold, a timer, an
increment value, and a decrement value. In addition, each
Managed Object Instance (MOI) has a counter. If the counter
exceeds the threshold for that MO Class the MOI is unstable. The
MOI counter is incremented by the increment value when a fault,
affecting the functionality, is received in a BTS reported Fault
Report. A timer is started for the MOI. When the timer expires, the
MOI counter is reduced by the decrement value for the MOIs MO
Class. When the MOI is brought back into operation the MOI
counter is checked. If the MOI counter exceeds the threshold for
that MO Class, the MOI is unstable and is classified as
permanently faulty.
VERIFYING BTS DATA
This verifies that the data the MO has stored in the BTS
corresponds to that stored in the BSC. Verification is not carried
out if the MO is to be tested. The data read from the BTS and
compared with the BSC consists of software version fault data,
state, and configuration data. If the software version or checksum is
wrong, the MO is loaded and tested, and the BTS parameters are
updated. If the fault data does not correspond and if the BTS
indicates a fault affecting the functionality, the MO is taken out of
operation. If a fault, not affecting the functionality, is indicated, the
BTS Alarm Handling is informed. The BSC fault data is updated
with the BTS fault data. If the configuration data does not
correspond, the MO is reconfigured.
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UPDATING BTS DATA
This function refreshes any BTS Internal Parameters that may have
been lost when the affected MO was taken out of operation. It
updates any data that was found to be inconsistent by utilizing the
Verifying BTS Data function. Once an MO is back in operation it
can be configured. This may result in logical channels being made
available for the traffic process.
CONFIGURATION OF THE BTS
The aim of this function is to match a configuration specification
with the available BTS equipment. The function configures the
BTS equipment, accordingly. Once the equipment has been set up
to match the configuration specification, this function attempts to
maintain the configuration. If insufficient BTS equipment is
available to match the configuration specification, the best possible
result is provided. In addition to the non-hopping configuration of
channels, the capability to maintain frequency hopping channels is
also provided. The configuration specification is provided by the
cell configuration function. This includes the nominal power levels,
required for the configuration of the cells, connected to the TG. In
addition, it includes groups of channel combinations together with
their desired ARFCN and, for a hopping system, Mobile
Allocation Index Offset (MAIO). This function provides all
channels that can be supported by BTS equipment to the cell
configuration with the ability to operate as BPCs.
TESTING THE AFFECTED MO
If the test indicates a fault, the MO is kept out of operation.
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FUNCTION CHANGE AND PROGRAM LOAD OF MO
FUNCTION CHANGE
The MO function change is the loading of predetermined software
packages in all loadable MOs, which are manually deblocked.
These MOs belong to a specific BTS manufacturer and are
administered by the BSC. The function change is performed
successively for each TG, and leaves the traffic on the rest of the
system unaffected. During the TG function change, the parallel
loading of TRUs and MOs is performed.
The software version defined per TRU or its TG includes a header
file and a loadable software file for each MO. The function change
assures the loading of the replacement version in the BSC in each
manually deblocked TRU and its subordinate deblocked MOs.
During the function change, the identity of the actual software
version is changed to the replacement software version.
After the function change, the MOs are brought back into
operation. The function change of MOs can be conditionally or
unconditionally ordered. For unconditional MO function changes,
no checks are performed to verify if these files already exist in the
TRU and the associated MOs. The replacement software is
reloaded to each TRU and subordinate MO. For conditional
function changes, the software reload for MOs takes place only if
the replacement software in the BSC does not correspond to the
operational software in the BTS. During this initial check, the
traffic is not interrupted. If the software checks fail, the traffic is
halted until the loading is complete and the MOs are operational.
After the function change, the updated software versions are used
for any subsequent automatic MO software loading. This assures
the operation of the BTS using the changed functionality. For MOs
that are manually blocked during the function change, only the
identity of the actual software version is changed. This software
version is reloaded when it is manually deblocked. If the command
is given to abort the function change process, it stops after
completing the software loading for the TG in progress. No
attempts are made at switching back to the previous TG
functionality, if new software versions have already been loaded in
the MOs.
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PROGRAM LOAD
The MO program load is the loading of predetermined software
packages in specific MOs, in service. These MOs belong to a
specific BTS manufacturer and are administered by the BSC. The
program load function allows the operator to load software in
operating MOs. The command initiated program load is performed
on an MO basis.
RXPLI:MOTY=RXOTG,LOAD,UC;
RXPLI:MO=RXOTG-0&&-6,START;
The MO program load follows the same procedure as a function
change. During the MO program load, software upload, file
transfer, and the loading of logical units take place. Command
initiated program loading of MOs can be ordered conditionally or
unconditionally. When an MO is specified for program loading, all
subordinate MOs are loaded simultaneously.
After the MO program load, the changed software version is
employed for any subsequent automatic software loading of the
MOs. If the command is given to abort the program load process, it
stops after completing the software loading of the MO, which is in
progress. No attempts are made at switching back to the previous
MO functionality, if new software versions are already loaded in
the MOs.
RXPLE:MO=RXOTG-1;
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Appendix A
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Appendix A
FEATURES
CHANGE OF TRAINING SEQUENCE CODE
RLDTC: CELL=cell, SCTYPE=sctype, TSC=tsc;
SCTYPE: subcell type
UL= underlaid
OL= overlaid
TSC: training sequence code. Numeral 0-7.
The purpose of the TSC is to determine the training sequence in a
burst. According to GSM, eight different sequences are permitted.
The training sequence allows the Viterbi-equalizer in the receiver
to create a mathematical model of the transmission channel (air
interface), and calculate the most probable transmitted data. By
default, the TSC is identical to the Base station Color Code
(BCC). Cells from the same cluster generally have the same BSIC.
If an overlaid network type 3/9 cluster is set on top of an underlaid
network type 4/12 cluster, the overlaid cells from a different 3/9
cluster still have the same BSIC and thus the same TSC. Therefore,
it is vital to change their TSCs according to the cluster they belong
to. This does not, however, change the BSIC. This change in the
TSC makes it easier for the Viterbi-equalizer to distinguish
between the same frequencies, used by the different reuse patterns
in the overlaid and underlaid subcell clusters.
The TSC is also used for IRC but only in dTRU, EDGE sTRU and
RBS 2308 and more modern TRU.
In case the MS receives a stronger signal from D because of
shadowing in B, the MS makes up a model for the down-link
channel from B. The MS knows its own TSC overlaid cell B. Thus
it can ignore the even stronger signal from overlaid cell D.
Different training sequences allow for a better transmission in case
of interference. In addition, the MS can differentiate between cells
from the overlaid and the underlaid network. Figure 4-11 illustrates
this.
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B
Interference
D
Figure A-8. Use of the TSC
LOCATING DISCONNECT DATA
RLLDC: CELL=cell, MAXTA=maxta, RLINKUP=rlinkup;
MAXTA: Timing advance limit when an MS is considered lost.
Numeral 0 - 63 bit periods (Normal range cell). Numeral 0 - 219 bit
periods (Extended range cell).
RLINKUP: Radio link timeout. Numeral 0-63 SACCH periods.
The maximum value of the radio link counter. A number of up-link
SACCH messages, within a certain time, cannot be decoded by the
BTS. The BTS will then disconnect the call. This number is
specified by RLINKUP.
LOCATING URGENCY DATA
RLLUC: CELL=cell, SCTYPE=sctype, QLIMUL=qlimul,
QLIMDL=qlimdl, QLIMULAFR= qlimulafr, QLIMDLAFR=
qlimdlafr, TALIM=talim, CELLQ=cellq;
QLIMUL: Quality limit up-link for handover. Numeral 0-100.
QLIMDL: Quality limit down-link for handover. Numeral 0-100.
QLIMULAFR: Quality limit up-link for handover for Terminals
using Fullrate AMR speech codecs. Numeral 0-100.
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QLIMDLAFR: Quality limit down-link for handover for
Terminals using Fullrate AMR speech codecs. Numeral 0-100.
The system constantly measures the transmission quality of both
the up-link and down-link connections. Another term for
transmission quality is BER. A high BER may result from a signal
strength that is too low, or from interfering signals. Separate
thresholds (QLIMULAFR & QLIMDLAFR) are set for
connections using AMR speech codecs due to the more robust
nature of AMR connections. The separate threshold for AMR
makes it possible to avoid unnecessary bad quality handovers for
terminals using AMR speech coders. Table 4-2 shows the
relationship between BER numeric quality values, as used in the
Ericsson system, and deci-transformed quality units (dtqu), as
specified by GSM:
BER before
channel decoder
< 0.2%
0.2 - 0.4 %
0.4 - 0.8 %
0.8 - 1.6 %
1.6 - 3.2 %
3.2 - 6.4 %
6.4 - 12.8 %
> 12.8 %
Value
dtqu
0
1
2
3
4
5
6
7
0
10
20
30
40
50
60
70
Table A-4.
The table above shows that a good quality (low BER) corresponds
to a low dtqu value. Poor quality corresponds to a high dtqu value.
If the quality value, as calculated in the averaging process, exceeds
either the Quality LIMit Down-link (QLIMDL) or the Quality
LIMit Up-link (QLIMUL), the system indicates an urgency
condition. QLIMUL and QLIMDL parameters determine
thresholds triggering an urgency handover.
TALIM: Timing advance limit for handover. Numeral 0-63 bit
periods (normal cell), 0-219 bit periods (extended range cell).
If an MS is close to the cell border, defined by the TA, a handover
will be triggered. The BSC compares the current average value of
TA to the defined TALIM. If the TA exceeds TALIM, the BSC
tries to hand the MS over to a suitable neighboring cell. If no
suitable neighbor is available, no handover will be executed. Since
GSM defines the maximum TA to be 63 bit periods, the TALIM
value must be smaller than 63 (TALIM < 63, normal cell).
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CELLQ: Cell quality. High or low.
An incoming MR initiates a new evaluation cycle. Depending on
the RPD processor load in the BSC where the locating function is
performed, it is possible to have the process started every second
MR. This can be adjusted using the parameter CELLQ. Processor
load can be controlled as follows:
• CELLQ=HIGH: means that a constantly good quality can be
expected within the cell. Every MR is evaluated, but the cycles
only start on the arrival of every second MR. As soon as the
transmission quality deteriorates, the system automatically
switches to calculation of handover criteria on the arrival of
every MR.
• CELLQ=LOW: means that transmission quality changes within
a broad range. The radio connection requires constant
supervision and quick reactions to poor conditions. Therefore,
the cycle is performed every time an MR arrives.
LOCATING PENALTY DATA
RLLPC: CELL=cell, PTIMHF=ptimhf, PTIMBQ=ptimbq,
PTIMTA=ptimta, PSSHF=psshf, PSSBQ=pssbq, PSSTA=pssta;
A handover attempt is not always successful. Sometimes a suitable
neighbor is found for handover (target cell), but the neighbor has
no idle channel available. In that case, the MS remains in the old
cell. One cycle later, the system attempts to hand the MS over to
the same congested cell again. When a successful handover occurs,
the system must avoid handing the MS back to the original cell
immediately after the previous handover. Otherwise, this can lead
to constant jumping between two cells (ping-pong effect).
Therefore, abandoned cells or congested cells are penalized.
Imposing a penalty works as follows. From the real (measured and
filtered) signal strength value, a predefined Penalty Signal Strength
value is subtracted. This value differs depending on the reason for
the handover attempt. The corresponding parameters are called:
PSSHF: applied to a target cell in case of a failed handover.
PSSBQ: applied to an abandoned cell in case of bad quality
handover.
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PSSTA: applied to an abandoned cell in case of the TA being
exceeded.
The effect of the penalty is that the penalized cell may be shifted to
a lower position in the basic ranking list.
The penalty is valid for a specified time period depending on the
reason for the handover attempt. The corresponding parameters
are:
PTIMHF: for a failed handover.
PTIMBQ: for bad quality.
In seconds. 0-600
PTIMTA: for timing advance exceeded.
Figure A-2 illustrates how a cell changes its position in the ranking
list depending on the penalty parameters.
A
B
C
D
Cell A (serving cell)
Cell A (serving cell)
Cell C (serving cell)
Cell C (serving cell)
Cell B
Cell C
Cell A
Cell B
Cell C
Cell D
Cell D
Cell A
Cell D
Cell E
Cell E
Cell D
Cell E
Cell B
Cell B
Cell E
Cell F
Cell F
Cell F
Cell F
before HO attempt
after HO failure to Cell B
after successful
handover to Cell C
after expiry of PTIMHF
Figure A-2. Penalty Handling
Situation A:
The system finds out that a handover in Cell A is required, due to
poor signal quality. Cell B is the best suitable candidate, but due to
congestion, Cell B is not accessible. Cell C is the next candidate.
Situation B:
Due to the failed handover, Cell B is penalized. That is, the value
PSSHF is subtracted from its real signal strength value. The
penalty is valid for a time period specified by PTIMHF.
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Situation C:
A handover to cell C is attempted and succeeds.
Situation D:
Cell C is now the serving cell. After PTIMHF expires, Cell B is
back in an upper position on the ranking list.
This type of penalty evaluation only works with cells in one and
the same BSC. In the cases with inter-BSC or inter-MSC handover,
another BSC is involved. The target BSC may not manage penalty
handling and therefore cannot penalize the abandoned cell with
PTIMBQ or PTIMTA. The target BSC might hand the call back to
the abandoned cell immediately. For this reason, the current BSC
must know if the target BSC supports penalty handling. This is
indicated with the parameter EXTPEN (command RLLOC). It is
defined for external cells. EXTPEN=ON means that penalty
handling is supported in the external cell. EXTPEN=OFF means
that it is not supported. After penalty evaluation, the locating
process enters the stage of Basic Ranking.
LOCATING FILTER DATA
RLLFC:CELL=cell, SSEVALSD=ssevalsd, QEVALSD=qevalsd,
SSEVALSI=ssevalsi, QEVALSI=qevalsi, SSLENSD=sslensd,
QLENSD=qlensd,
SSLENSI=sslensi,
QLENSI=qlensi,
SSRAMPSD=ssrampsd, SSRAMPSI=ssrampsi;
SSEVALSD: Signal strength evaluation selection at speech/data.
Numeral 0-9.
SSEVALSI: Signal strength evaluation selection at signaling only.
Numeral 0-9.
SSLENSD: Filter length for signal strength, speech/data. Numeral
1-20.
SSLENSI: Filter length for signal strength, signaling. Numeral 120.
SSRAMPSD: Ramping length for signal strength, speech data.
Numeral 1-20.
SSRAMPSI: Ramping length for signal strength, signaling.
Numeral 1-20.
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QEVALSD: Quality evaluation selection at speech/data. Numeral
1-9.
QEVALSI: Quality evaluation selection at signaling only.
Numeral 1-9.
QLENSD: Filter length for quality, speech data. Numeral 1-20.
QLENSI: Filter length for quality, signaling. Numeral 1-20.
Filtering can be performed on both signal strength and transmission
quality. Transmission quality corresponds to Bit Error Rate
(BER). Furthermore, the process of averaging is separated in the
evaluation for signaling (SI) channels, for example, SDCCH, and
evaluation for speech and data channels (SD), for example, TCH.
Therefore, the parameters QLENSD and QLENSI determine the
filter length for quality evaluation; the parameters SSLENSD and
SSLENSI determine the filter length for signal strength evaluation
on speech and data channels or signaling channels respectively. For
easy handling of averaging/filtering, the BSC keeps predefined sets
of filters. These predefined filters can be selected using an
EVALuation set. As with filter length, they apply to both signal
strength and quality, separated by speech and data channels and
signaling channels. The parameters are QEVALSD, QEVALSI,
SSEVALSD and SSEVALSI.
LOCATING HIERARCHICAL DATA
RLLHC:CELL=cell, LAYER = layer, LAYERTHR =layerthr,
LAYERHYST
=
layerhyst,
PSSTEMP=psstemp,
PTIMTEMP=ptimtemp, FASTMSREG=fastmereg;
RLHBC:CELL=cell, HCSBANDHYST =hcsbandhyst, HCSBAND
= hcsband, LAYER= layer, HCSBANDTHR=hcsbandthr;
HCS Bands and Layers
The network can be divided into up to eight different HCS layers.
The layers are grouped into HCS bands. An example of how layers
can be grouped into bands is illustrated in Figure A-3.
Up to eight layers may be defined using HCS. The layers are
distributed in ascending order in up to eight HCS bands. A lower
HCS band thus only includes lower layers, compared to a higher
HCS band.
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The layers can be distributed over the HCS bands in a variety of
combinations. For example, all eight layers may be present in one
HCS band, or there may be one layer in each HCS band.
The priority of a cell is given by associating a layer to the cell.
Each layer also belongs to an HCS band. The lower the layer (and
HCS band), the higher the priority.
The layer and band definition can be based on how much traffic the
cells would capture with just basic ranking, on how much traffic
they, at a maximum, can be dimensioned for, and on how much the
cells interfere with the rest of the network, etc.
1800 MHZ
Dedicated for indoor
1800 MHZ
900 MHZ
Dedicated subband
900 MHZ
Band 2
Band 4
Band 6
Band 8
Layer 2
PICO
L3
L4
MICRO MACRO
High Priority
Layer 5
PICO/MICRO
L6
L7
MICRO MACRO
Low Priority
Figure A-3. An Example of How the Layers and HCS Bands Can
Be Distributed.
With eight layers, it is possible to assign unique layers to indoor
cells, microcells, macrocells and, possibly, umbrella cells of each
system type.
The first issue is to define the HCS bands and prioritize them in an
efficient way with respect to capacity.
The low loaded system type should have priority over the higher
loaded system type.
Dedicated sub bands for indoor or microcells should have priority
over larger cells within their own system type.
Each HCS band may be divided further into indoor cell prioritized
over microcells prioritized over macrocells.
LAYERTHR =layerthr
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Layer Threshold
The layer threshold decides if the cell should be prioritized over
stronger cells of the same HCS band.
The layer threshold, LAYERTHR, is used to decide the trade-off
between getting the maximum capacity from cells and acceptable
levels of interference between cells within an HCS band.
LAYERHYST = layerhyst
Hysteresis
To prevent consecutive handovers, due to fluctuations in signal
strength, a hysteresis is applied to each signal strength threshold.
For the hysteresis, the default values LAYERHYST and
HCSBANDHYST = 2 are recommended. If there are indications of
an excessive number of handovers between layers, it is more likely
to be the result of bad quality urgency handovers, rather than a too
low hysteresis.
An Example of a Layered Cell Structure with 3 HCS Bands and 5 Layers
In Figure 4-19 the network is divided into three HCS bands.
The 1,800 frequencies are divided into two sub bands where one
band does not interfere with the other except for the two adjacent
frequencies around the band split. One of the 1800 bands is
dedicated for indoor cells. The third HCS band is the 900 MHz
band. The 900 band contains microcells in layer 6 and macrocells
in layer 7. The 1800 main band contains microcells in layer 3 and
macrocells in layer 4. The 1800 sub band contains only layer 2,
used for indoor cells.
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Figure A-4 An Example of a Layered Cell Structure with 3 HCS Bands
and 5 Layers.
Layer 3 in figure 3 may suffer from co- or adjacent channel
interference from layer 4. Therefore a microcell in layer 3 should
only be prioritized over a stronger 1800 MHz macrocell (layer 4) if
its signal strength is high, for example, above a layer threshold of –
75 dBm.
If the 1800 MHz microcell in the example is surrounded by strong
900 MHz cells but no (layer 4) 1800 MHz macrocell, it can be
prioritized over 900 MHz micro- and macrocells down to a lower
band threshold of for example -95 dBm.
The lowest setting of the layer threshold is dependent on the
interference situation within the band. A high threshold is
preferable with respect to interference. The band will still be
prioritized due to the lower HCS band threshold.
SIGNAL STRENGTH THRESHOLDS
Two signal strength thresholds exist, which decide if the signal
strength is sufficient for the cell to be prioritized.
Band Threshold
The band threshold determines if the cell should be prioritized over
stronger cells from other HCS bands.
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The HCS band signal strength threshold, HCSBANDTHR , is used
to determine if the HCS band in question is represented with
sufficient signal strength to be prioritized at all.
Between the cells of different bands there is no interference and the
borders of the preferred band are limited by noise. If the load
situation requires, the band threshold may be set rather low. A
margin is, however, required to delay handover by a few seconds in
case the signal strength falls drastically.
PSSTEMP: Signal strength penalty, temporary offset in dB.
Numeral 0-63.
PTIMTEMP: Penalty duration in seconds. Numeral 0-600.
Since lower layer cells have priority over cells from higher layers,
the system always tries to hand a “busy” MS down to a lower layer.
This may cause a large number of handovers.
Figure 4-20 shows what happens if the MS is moving fast along the
black line through an area with two layer-1 cells B and C (white
area) and a layer-2 cell A (gray area).
Cell A: layer-2
Cell C: layer-1
Cell B: layer-1
HO
HO
HO
HO
HO
HO
Figure A-5. Fast Moving MS
Four of these handovers can be saved. This is accomplished as
follows:
The first time the cell reports cell B in the Measurement Report
(MR), cell B is “punished” by subtracting a penalty signal strength
PSSTEMP from the real value. The penalty is valid for an interval
PTIMTEMP. The penalty shifts the neighbor to a lower position
in the ranking list. It is even excluded from evaluation if the signal
strength drops below MSRXMIN. If the MS loses sight of cell B
prior to PTIMTEMP expiring, no handover will occur.
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How to Estimate PTIMTEMP
The black line represents a road with a speed limit of 60 km/h. The
operator tries to avoid frequent handovers. PTIMTEMP can then be
estimated as follows:
Measurements from test drives show that the distance s between
the first report of cell B in MR and the disappearance of cell B
from MR is 1 km. The car has a speed of v=60 km/h. The time
between the two points is thus:
t = s/v = 1/60 h = 1 minute
So PTIMTEMP must be greater than 1 minute. If the MS remains
longer in the cell B area, cell B joins the candidate list as a nonpenalized layer-1 cell.
FASTMSREG: Handling of fast moving mobiles switch. ON or
OFF.
To enhance the use of parameters PSSTEMP and PTIMTEMP,
especially for fast moving mobiles, the parameter FASTMSREG
may be used.
A fast moving mobile will be identified by counting the number of
inter cell handovers during a certain time period. If the handover
intensity increases above a threshold value, and the function
‘handling of fast moving mobiles' is switched on in the new cell,
the mobile will not use the HCS structure when ranking cells in
locating. Instead, the ranking is based on the best signal strength
before the next inter-cell handover has occurred. The handover
intensity algorithm is nulled and normal ranking with HCS is used
again. New deviations from HCS locating may occur only if the
handover intensity increases again during the call.
The rate of handovers for a mobile is monitored, regardless of
whether the function is switched on or off in a cell, since later on, a
handover to a cell where the function is switched on, might occur.
The parameter FASTMSREG is used to switch the function on and
off. It has the value range ON, OFF with default OFF, and can be
set per cell.
Two new parameters THO, defining the time interval for
measuring the number of handovers, and NHO (refer to command
RLLBC), defining the number of handovers, allowed during THO,
before ranking without HCS ranking is used and set per BSC.
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INTRA-CELL HANDOVER LOCATING DATA
RLIHC:
CELL
=cell,
SCTYPE=sctype,
IHO=iho,
MAXIHO=maxiho,
TMAXIHO=tmaxiho,
TIHO=tiho,
SSOFFSETULP/N=ssoffsetulp/n,
SSOFFSETDLP/N=ssoffsetdlp/n, QOFFSETULP/N=qoffsetulp/n,
QOFFSETDLP/N=qoffsetdlp/n,
SSOFFSETULAFRP/N=ssoffsetulafrp/n,
SSOFFSETDLAFRP/N=ssoffsetdlafrp/n,
QOFFSETULAFRP/N=qoffsetulafrp/n,
QOFFSETDLAFRP/N=qoffsetdlafrp/n,
An intra-cell handover is a handover from one dedicated channel to
another within the same cell. This may include the change to
another carrier. The reason for intra-cell handover can be bad
transmission quality due to co-channel interference or Rayleighfading.
SCTYPE: subcell type
UL= underlaid
OL= overlaid
All= both UL and OL
IHO: Intra-cell handover switch. ON or OFF.
MAXIHO: Maximum number of intra-cell handovers. Numeral 015.
TMAXIHO: Timer for handover counter. Numeral 0-60 (seconds).
TIHO: Intra-cell handover inhibition timer.
The intra-cell handover evaluation is only performed when these
conditions are fulfilled:
•
•
IHO = ON
IHOSICH switches intra-cell handover ON or OFF for the
signaling channel
If the intra-cell handover is switched on, it may be inhibited
according to the following conditions:
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•
•
A number
occurred.
MAXIHO
consecutive
intra-cell
handovers
An intra-cell handover is considered “consecutive”, if the next
one occurred within an interval of TMAXIHO – see Figure 421 and 4-22.
TMAXIHO
TMAXIHO
TMAXIHO
TMAXIHO
a) consecutive
b) not consecutive
Figure A-6. Timers for Intra-cell Handover
The last intra-cell handover in a row of MAXIHO starts an
inhibition-timer TIHO. As long as TIHO has not expired, no
further intra-cell handover is executed. This prevents the system
from jumping from channel to channel. Each intra-cell handover
also starts the timer TINIT (refer to Locating).
TMAXIHO
TMAXIHO
TMAXIHO
TIHO
Figure A-7. MAXIHO = 3
SSOFFSETULP/N, SSOFFSETDLP/N,
QOFFSETULP/N,
QOFFSETDLP/N,
SSOFFSETULAFRP/N,
SSOFFSETDLAFRP/N,
QOFFSETULAFRP/N,
QOFFSETDLAFRP/N
These parameters are used in a quality vs. signal strength function
which, for every signal strength level, gives a minimum accepted
quality level.
LOCATING OVERLAID SUBCELL DATA
RLOLC:CELL=cell, LOL=lol, LOLHYST=lolhyst, TAOL=taol,
TAOLHYST=taolhyst,
DTCBN=dtcbn/DTCBP=dtcbp,
DTCBHYST=dtcbhyst, NDIST=ndist, NNCELLS=nncells;
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TAOL: Timing Advance Overlaid, timing advance threshold in bit
periods. Numeral 0-61.
TAOLHYST: Hysteresis for timing advance in bit periods.
Numeral 0-61.
The parameter TAOL and a corresponding hysteresis TAOLHYST
determine the range of the overlaid subcell. In case of a handover
from an overlaid subcell to an underlaid subcell, the handover is
performed if the measured TA exceeds the value TAOL, or,
including the hysteresis, if:
TA ≥ TAOL + TAOLHYST
In case of a handover from an underlaid subcell to an overlaid
subcell, the handover can be performed if the measured TA is
below the value TAOL, or including the hysteresis, if:
TA ≤ TAOL − TAOLHYST
Signal strength criteria must also be fulfilled (LOL, LOLHYST).
LOL: Pathloss threshold in dB. Numeral 0-150.
LOLHYST: Hysteresis for pathloss in dB. Numeral 0-63.
In an overlaid subcell, the output power BSTXPWR_OL is used. In
an underlaid subcell, the output power used is BSTXPWR_UL.
The handover upward from an underlaid subcell to an overlaid
subcell is performed at a threshold defined as:
RXLEV = BSTXPWR_UL − LOL + LOLHYST
For simplification the LOLHYST parameter is omitted in Fig. A-8.
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RXLEV
BSTXPWR_UL
LOL
BSTXPWR_OL
distance from BTS
HO from OL to UL
with hysteresis
Figure A-8. Subcell Handover, UL to OL
The handover downward from an overlaid subcell to an underlaid
subcell –see Figure 4-24 is performed at a threshold defined as:
RXLEV = BSTXPWR_OL − LOL − LOLHYST
For simplification the LOLHYST parameter is omitted in Fig. A-9
RXLEV
BSTXPWR_UL
BSTXPWR_OL
LOL
distance from BTS
point of HO from OL to UL
without hysteresis
Figure A-9. Subcell Handover, OL to UL
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DTCBN: Negative distance to cell border. Numeral 1-63
DTCBP: Positive distance to cell border. Numeral 0-63
DTCBHYST: Distance to cell border hysteresis Numeral 0 - 63
NNCELLS: Number of neighboring cells. Numeral 1-5
NDIST: Neighboring cell distance Numeral 0-63
CHANNEL ALLOCATION PROFILE
RLHPC: CELL=cell, CHAP=chap;
CHAP: Channel allocation profile. Numeral 0-10.
CHAP is used as a strategy for the allocation of channels in a cell.
DYNAMIC MS POWER CONTROL CELL DATA
RLPCC: CELL=cell, SCTYPE=sctype, SSDESUL=ssdesul,
SSLENUL=sslenul, LCOMPUL=lcompul, QDESUL=qdesul,
QLENUL=qlenul, QCOMPUL=qcompul, REGINTUL=regintul,
DTXFUL=dtxful;
SSDESUL: Desired signal strength, up-link. Numeral 47-110
(dBm).
SSLENUL: Length of signal strength filter, up-link. Numeral 3-15
(SACCH periods).
LCOMPUL: Pathloss compensator factor, up-link. Numeral 0-100
(%). For 0% no regulation towards SSDESUL is performed.
QDESUL: Desired quality, up-link. Numeral 0-70 (dtqu).
QLENUL: Length of quality filter, up-link. Numeral 1-20
(SACCH periods).
QCOMPUL: Quality deviation compensator factor, up-link.
Numeral 0-60 (%).
REGINTUL: Regulation interval up-link. Numeral 1-30 (SACCH
periods).
DTXFUL: Number of measurement periods before FULL
measurement periods are used, up-link. Numeral 0-40 (SACCH
periods).
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DYNAMIC BTS POWER CONTROL CELL DATA
RLBCC: CELL=cell, SCTYPE=sctype, SDCCHREG=sdcchreg,
SSDESDL=ssdesdl, REGINTDL=regintdl, SSLENDL=sslendl,
LCOMPDL=lcompdl, QDESDL=qdesdl, QCOMPDL=qcompdl,
QLENDL=qlendl, BSPWRMINP/N=bspwrminp/n;
SDCCHREG: SDCCH regulation switch. ON or OFF.
SSDESDL: Desired signal strength, down-link. Numeral 47-110
(dBm).
REGINTDL: Regulation interval, down-link. Numeral 1-10
(SACCH periods).
SSLENDL: Length of signal strength filter, down-link. Numeral 315 (SACCH periods).
LCOMPDL: Pathloss compensator factor, down-link. Numeral 0100 (%).
QDESDL: Desired quality, down-link. Numeral 0-70 (dtqu).
QCOMPDL: Quality deviation compensator factor, down-link.
Numeral 0-100 (%).
QLENDL: Length of stationary quality filter, down-link. Numeral
1-20 (SACCH periods).
BSPWRMINP: Minimum base station Effective Radiated Power
(ERP) positive offset for the absolute RF channel in the cell
defined for non BCCH frequencies. Numeral 0-50 (dBm).
BSPWRMINN: Minimum base station Effective Radiated Power
(ERP) negative offset for the absolute RF channel in the cell
defined for non BCCH frequencies. Numeral 1-20 (dBm).
CELL LOAD SHARING
RLLCI: CELL=cell;
This command activates the cell load sharing function.
CELL LOAD SHARING DATA
RLLCC: CELL=cell, CLSLEVEL=clslevel, CLSACC=clsacc,
HOCLSACC=hoclsacc, RHYST=rhyst, CLSRAMP=clsramp;
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CLSLEVEL: Percentage of available full rate capable traffic
channels on which or below which cell load sharing evaluations are
initiated. CLSLEVEL must be less then CLSACC. Numeral 0-99
(%).
CLSACC: Percentage of available full rate capable traffic
channels below which no handovers, due to cell load sharing, will
be accepted. Numeral 0-100 (%).
HOCLSACC: Handover, due to cell load sharing, accepted to this
cell. ON or OFF.
RHYST: Hysteresis reduction factor. Numeral 0-100 (%).
CLSRAMP: Cell load sharing ramping time. Numeral 0-30
(seconds).
The purpose of the Cell Load Sharing function is to distribute
traffic load to other cells during traffic peaks. This is done by
moving established connections from cells with high traffic to
neighboring cells with idle resources. As a result, the traffic load is
distributed more evenly in the network and the congestion
probability in a cell decreases, that is, the probability of a failed
channel allocation, due to congestion in the cell, is reduced.
The level of idle traffic channels where traffic is removed from a
cell is one major criterion. A second criterion is the level of
rejection of traffic, that is, the number of idle TCHs in the target
cell. At this level, shifted traffic, due to cell load sharing, is
rejected.
Cell load sharing is not used between BSCs or between cells with
different hierarchical levels. Cell load sharing is applicable to TCH
channels only. The evaluation takes place immediately after the
basic ranking in the locating algorithm. It is not applicable to an
urgency handover,
The function performance is regulated by parameters which are
changeable via operator commands. Load sharing must be
activated for both BSC and the cells.
If a cell is to participate in LS, it can hand over a call to another
(worse) cell, or it can accept handovers from other cells. For
acceptance of a shifted call, the traffic level in the target cell must
be below a certain acceptance level, CLSACC. If a certain
percentage of all TCHs in the cell is already busy (the traffic level
is above CLSACC), handovers due to LS are not accepted. Of all
TCHs (100%), more than (CLSACC)% TCHs should remain idle.
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100% idle
0% idle
CLS active
CLS-handover accepted
CLSLEVEL
Cell A
Cell B
CLSACC
CLSACC
CLS-handover accepted
CLSLEVEL
CLS active
0% idle
100% idle
Figure A-10. Cell Load Sharing Parameters
If the number of idle TCHs drops below a level defined by
CLSLEVEL, the cell in question initiates a CLS-handover to a
neighboring cell. Clearly, CLSLEVEL must always be smaller than
CLSACC. Figure 4-30 illustrates this.
Acceptance of handovers can generally be allowed or prohibited by
a CLS-switch HOCLSACC. With HOCLSACC=OFF, the cell
does not accept the handover. With HOCLSACC=ON, it accepts
the handovers.
Only connections that are close to handover are moved. For this
reason, the hysteresis area between cells is used to select the
connections to be moved. Only cells, which are ranked worse than
the serving cell, are considered target cells. Basically, the ranking
of cells is redone using the hysteresis used in basic ranking (KYST,
LHYST, TRHYST). However, these hysteresis-values are now
adjusted by a ramping hysteresis (RHYST). RHYST applies to all
types of hysteresis.
RHYST can be defined as:
•
•
•
RHYST = 0%, the normal hysteresis (xHYST) is applied.
RHYST = 50%, no hysteresis is applied.
RHYST = 100%, the negative value of xHYST is applied.
This figure illustrates the handover border when moving from cell
A to cell B. The indicated values of RHYST apply to cell A.
Offsets are not respected:
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nominal border of HO
Cell A
border for HO from A to B
for RHYST=100%
Cell B
RHYST=50%
border for HO from A to B
for RHYST=0%
Figure A-11. Cell Load Sharing Hysteresis
A transition between the lower (0%) and the upper end (100%) is
possible. Thus, RHYST defines a corridor of load sharing around
the serving cell. Any MS in this corridor may be subject to load
sharing. Since all types of hysteresis are related to a neighboring
cell, the corridor may be shaped differently towards different cell
neighbors.
A problem might be that, if the traffic level exceeds CLSLEVEL,
all MSs in the corridor become subject to LS simulataneously. This
creates a sudden increase in processor load. In the worst case, an
uncontrolled shift leads to congestion in a target cell which again
can lead to dropped calls. Therefore, the MS which is close to the
neighbor, is handed over first, not those far away.
The problem is solved with the principle of time dependent
ramping. It is controlled by CLSRAMP. CLSRAMP specifies an
interval in which the value RHYST is ramped up from 0 to its final
value. This changes the corridor size in time. The mobiles which
are closest to the handover border are handled first. Figure 4-31
illustrates the feature.
ADVANCED SINGLE SLOT ALLOCATION
RLGAC : CELL=cell, [CHGR=chgr], SAS=sas;
CELL: Cell name
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CHGR: Channel Group
SAS: Single Slot allocation Strategy. Values for SAS are
QUALITY, MAIO and MULTI.
TCH allocation can be undertaken based on one of these three
strategies (i.e. QUALITY, MAIO and MULTI slot). It is possible
to choose between the three strategies for single slot allocation
based on the preferred traffic mix in the radio network on a per cell
basis.
TCH allocation based on QUALITY is based on the channel
quality data provided by the feature Idle Channel Measurement as
described previously.
TCH allocation with MULTI consideration leaves as many idle
channels as possible for multislot calls and will therefore increase
the probability of having consecutive channels available for
incoming multislot traffic. The MULTI strategy enhances
allocation of multiple timeslots for both CS and PS data calls.
TCH allocation based on MAIO (Mobile Allocation Index Offset)
consideration is recommended when it is of utmost importance to
minimize the interference from co-channels and adjacent channels
within and between cells. This strategy gives preference to
channels with MAIO that minimizes interference.
The choice of strategy is made per channel group and it is possible
to configure more than one strategy in a cell. If more than one
strategy is configured in a cell, channels with QUALITY strategy
will be allocated first, second are channels with MAIO strategy and
finally channels with MULTI slot strategy.
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AMR CODEC SETS
AMR is a new speech codec type that adapts the speech codec
bitrate and channel coding according to the radio environment.
AMR can be used to improve speech quality, increase radio
network capacity or both. AMR is available for use in full rate
channels (AMR FR).
AMR FR gives significantly better speech quality than Enhanced
Full Rate (EFR) under severe radio conditions.
Up to doubled capacity with AMR FR, since the improved
robustness makes it possible to add more transceivers and tighten
the frequency reuse.
In order to use AMR an Active Codec Set has to be defined. A
codec set consists of a selection of up to 4 of the available codec
modes. For each codec set there is an associated set of decision
thresholds that determine which codec mode that should be used at
a certain C/I. The codec mode changes are not audible and it is
possible to change codec mode every second speech frame but only
to the closest higher or lower codec mode in the codec set.
Different codec modes can be used on the uplink and downlink (the
codec set is the same). It is the receiving side (MS and BTS) that
performs quality measurements on the incoming link to perform
the codec mode adaptation.
There are two predefined codec sets that can be chosen as the
Active Codec Set, i.e. the included codec modes and their
associated threshold cannot be changed.
These codec sets are:
· 10.2, 6.7, 5.9 and 4.75
· 12.2, 7.95, 5.9 and 4.75
AMR is also standardized for use in UMTS systems, which enables
full speech service transparency between an operators 2G and 3G
systems.
The list of codec sets has been extended with two new codec sets
that can be manually configured.
RLADC changes an existing AMR codec set.
RLADC:SET=set, MODE=mode...[,THR=thr...,][ HYST=hyst...];
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HYST: is the hysteresis used along with the Threshold to avoid
continuous rapid changes between two codec modes.
MODE: is the codec mode that shall be included in the codec set
(the bit rate of the coded speech after the speech encoding),
expressed as a numeral between 1 and 8, and defined in ascending
order.
SET is the AMR Codec Set changed by the operator.
FR3 - Full Rate codec set 3.
FR4 - Full Rate codec set 4.
HR3 - Half Rate codec set 3.
HR4 - Half Rate codec set 4
THR: stands for threshold and it is the decision criteria for
changing the codec mode in the codec set, expressed as a numeral
between 0 and 63, in steps of 0.5 dB and defined in ascending
order
AMR POWER CONTROL
The RLAPC command changes cell unique data used by the
dynamic Mobile Station (MS) power control and the dynamic Base
Transceiver Station (BTS) power control algorithms for AMR FR
channels see fig 4-33
Separate regulation targets for MS/BTS Power
Control
– Only for AMR FR
– AMR terminals use less power
– AMR codec can handle the increased bit error
Figure A-12. AMR Power control
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RLAPC:CELL=cell, SCTYPE=sctype, SSDESDLAFR=ssdesdlafr,
QDESDLAFR=qdesdlafr,
SSDESULAFR=ssdesulafr,
QDESULAFR=qdesulafr;
SSDESDLAFR: Desired signal strength for the codec type AMR FR,
downlink Numeral 47 – 110 dBm
SSDESULAFR: Desired signal strength for the codec type AMR FR,
uplink Numeral 47 – 110 dBm
QDESDLAFR: Desired quality for the codec type AMR FR, downlink
Numeral 0 - 70 dtqu
QDESULAFR: Desired quality for the codec type AMR FR, uplink
Numeral 0 - 70 dtqu
RLAPI:CELL=cell;
This command initiates Adaptive Multi Rate (AMR) power control
in a cell.
DYNAMIC HR ALLOCATION
This feature allows allocation of full rate or half rate channels
according to the traffic situation in the cell for dual rate mobiles.
Half rate channels will be allocated when there is a risk for
congestion in a cell, otherwise full rate channels will be selected.
Now it is also possible to differentiate between AMR and non
AMR coding, where AMR has preference see figure A-13.
Operator setable
EFR
AMR
Traffic threshold:
New calls allocated
HR
EFR
AMR
EFR
EFR
AMR
AMR
•
•
Use HR only when and where it is needed
Better utilization of AMR HR
Figure A-13 - Dynamic HR Allocation
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RLDHC: CELL=cell, DHA=dha, DTHAMR=dtamr,
DTHNAMR=dtnamr;
DHA: Dynamic Half Rate (HR) Allocation. ON/OFF
DTHAMR: Dynamic HR Allocation threshold for Adaptive Multi
Rate (AMR) capable mobiles. Numeral 0-100 %
DTHNAMR: Dynamic HR Allocation threshold for mobiles not
capable of AMR. Numeral 0-100 %
See figure A-14 for an illustrated procedure
Is the mobile dual rate?
NO
YES
Is the mobile AMR
HR capable?
NO
YES
Is the amount of idle
FR below the
DTHAMR threshold?
NO
Is the amount of idle
FR below the
DTHNAMR threshold?
YES
Allocate
AMR HR
NO
Allocate
Wanted FR
YES
Allocate HR
Figure A-14. Dynamic HR Allocation procedure
DYNAMIC HR/FR ADAPTION
Dynamic FR/HR Adaptation makes it possible to change the
channel rate for ongoing speech calls. It can be changed from full
rate to half rate at congestion and from half rate to full rate at poor
radio link quality. This feature will both increase capacity and
maintain adequate speech quality.
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The limit for when each cell should start allocating HR where
possible is set on a per cell basis. See figure A-15.
Operator setable
Congestion threshold:
Existing calls
reallocated HR
EFR
EFR
AMR
AMR
EFR
EFR
AMR
AMR
•
Capacity boost from HR only when needed to avoid congestion
Figure A-15. FR/HR adaptation
RLDMC:CELL=cell,
DMQB=dmqb,
DMQG=dmqg,
DMQBAMR=dmqbamr,
DMQBNAMR=dmqbnamr,
DMQGAMR=dmqgamr,
DMQGNAMR=dmqgnamr,
DMTHAMR=dmthamr, DMTHNAMR=dmthnamr;
DMQB: Dynamic Half Rate (HR) to Full Rate (FR) Mode
Adaptation due to bad quality. Values on or off.
DMQBNAMR is Channel quality threshold for mobiles not
capable of AMR using a HR traffic channel. 1-100 (45)
DMQG is Dynamic FR to HR Mode Adaptation quality
evaluations. Values on or off.
DMQGAMR is Channel quality threshold for AMR capable
mobiles using a FR traffic channel. 1-100 (35)
DMQGNAMR is Channel quality threshold for mobiles not
capable of AMR using a FR traffic channel. 1-100 (30)
DMTHAMR is Dynamic FR to HR Mode Adaptation threshold
for AMR capable mobiles. 1-100 (20)
DMTHNAMR is Dynamic FR to HR Mode Adaptation threshold
for mobiles not capable of AMR. 1-100 (10)
RLDMI:CELL=cell, DMQB, DMQG;
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GSM BSC Operation
CALL QUEUING
Call Queuing enables prioritization of subscribers when there is
congestion in the radio network. See figure A-16.
Queuing allowed?
Prio: 3
3
2
1
1
Figure A-16. Call Queuing
Call Queuing makes it possible place subscribers in a queue,
waiting for a traffic channel when there is congestion in a cell. The
queue is sorted in order of priority, giving subscribers with high
priority access to traffic channels before lower prioritized
subscribers. Compared to preemption where ordinary subscribers
might be disconnected to make room for high priority subscribers,
Call Queuing provides priority access without disrupting the
service of ordinary subscribers. Another advantage of Call Queuing
is that traffic resources do not have to be reserved, and capacity is
not wasted when priority subscribers are not present.
Since each subscriber occupies an SDCCH channel while they are
being queued (up to 60s depending on operator setting), it is
important to adjust the queue length for each cell so that SDCCH
congestion is avoided. In case the queue is full, high priority
subscribers will remove subscribers with lower priority from the
queue. The maximum queue time can also be configured, and
subscribers that have been in the queue for too long will also be
removed.
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Call Queuing is supported for mobile originating calls, mobile
terminated calls and handover. It is possible to prioritize handover
before set up of new calls. Call Queuing only applies to
connections requiring a single timeslot, which means that
nontransparent multislot data calls will only be allocated one
timeslot initially, while transparent connections requesting multiple
timeslots will be rejected.
The following new Exchange properties are introduced set with
command RAEPC.
MSQUEING - Used to switch CQ ON and OFF. Default=OFF.
MSQASSTIME - Indicates the maximum time a PC can stay in
queue, if queued due to assignment. Value range: 1 - 60 s, default
30 s.
MSQHOPRIO - Indicates whether Handover has priority over
Assignment or not at queue ranking. Default: No priority for
Handover.
RLMQC: CELL=cell, RESLIMIT=reslimit, QLENGTH=qlength;
Where:
CELL: is the designated cell
RESLIMIT: is Channel resource limit. This parameter indicates
the percentage of radio channel resources, that is, Traffic Channel
Fullrate (TCH/F) and Traffic Channel Halfrate (TCH/H) that are
allocated to priority connections before starting to give available
channels to non-priority connections. Numeral 1 – 100. (25)
QLENGTH: is Maximum queue length in a cell. This parameter
determines the maximum number of Priority Connections (PC) that
can be inserted in the queue. Numeral 0 – 32. (5)
TCHs allocated for PCs
TCHs allocated for non PCs
Free
TCHs
TCH allocation:
- Allowed for PCs
- Not allowed for
non-PCs
TCH allocation:
- Allowed for PCs
- Allowed for nonPCs
by RESLIMIT
75 %
Total no of TCHs per
cell
RESLIMIT (50%)
25 %
Figure A-17 - CQ PC versus non PC, when a queue exists
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Requires that the MSC supports Queuing. Note that the sending of
priority elements from the HLR to the MSC/VLR requires that
MAP V2 is used in the MSC/VLR and the signaling is the standard
version.
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