EPFL
Section Systèmes de Communication
GPRS
« First steps toward Wireless data »
Frédéric Michaud
Network Development Engineering
27/01/2004
June 2002 V1.0
Page 1
GPRS Part 1
Content
From Theory…
INTRODUCTION
ARCHITECTURE
MOBILITY MANAGEMENT
SESSION MANAGEMENT
RADIO RESOURCE MANAGEMENT
January 2004
F. Michaud – GPRS course
Page 2
Introduction
General Packet Radio Service:

a way to extend packet transfer up to the mobile station
GSM
–
Circuit Switch architecture
–
–
–
January 2004
GPRS
–
Packet Switch architecture
Indirect access to IP
network
–
Too sensitive connection
for data (today)
End to End IP service
(mobile = IP host)
–
Re-use BSS architecture
–
New core architecture
–
Max theoretical rates ~170
kbps
Expensive solution for data
network (HSCSD)
F. Michaud – GPRS course
Page 3
Architecture
Network Diagram
NSS
HLR
MSC/VLR
ISP External
Network
GPRS Core Network
Gc
Gr
Gi
Gs
SGSN
A
Gn
Gn
BSS
GPRS
IP Backbone
Gb
Gn
Transcoder
Ater
BSC
Charging
Gateway
Um
Gn
Border
Gateway
Gp
Abis
Inter PLMN
Backbone
BTS
January 2004
GGSN
DNS
F. Michaud – GPRS course
Page 4
Architecture
evolution of BSS network
New hardware in BSS: Packet Controlling Unit (PCU)

• can be compared to TRAU function in GSM
• generally located in the BSC
• heart of the packet transmission in BSS network
• allow the dynamic traffic allocation
BTS
• Provide the radio resource management mechanism, adapted to
packet transfer
PCU
SGSN
buffer
RLC
RLC
RLC
LLC
LLC
LLC
buffer
buffer
Gb
Abis
January 2004
F. Michaud – GPRS course
Page 5
Architecture
New core equipments
HLR
VLR
Charging Gateway
External
IP world
PCU
GGSN
IP network
PCU
SGSN
• Packet routing (IP – BSS)
• Mobility Management
• Session Management
• Charging
• Cyphering and compression

GGSN
• GPRS Tunneling (PLMN – internet)
• Charging
• O&M (Operation & Maintenance)
• Lawful interception
Other equipment:
 Border Gateway, Charging Gateway, DNS, Firewalls
January 2004
F. Michaud – GPRS course
Page 6
Mobile equipment
Three types of Mobile Classes

CLASS A: « Rolls Royce »
CS Core Network (GSM)
Simultaneous CS/PS Paging
Simultaneous CS/PS data transfer
PS Core Network (GPRS)

CLASS B: « Standard »
CS Core Network (GSM)
Simultaneous CS/PS Paging
CS call or PS data transfer
PS Core Network (GPRS)

CLASS C: « Cheap »
CS Core Network (GSM)
CS mode (GSM only) or PS mode (GPRS only)
PS Core Network (GPRS)
January 2004
F. Michaud – GPRS course
Page 7
Mobility Management
Mobile States

IDLE
–
not attached to GPRS
–
MS is not reachable
IDLE
GPRS Attach
STANBY
timer
expiry
GPRS Detach

READY
READY timer expiry
Force to STANBY
–
MS known down to Cell by SGSN
–
May receive/transmit packets
–
No Packet paging required
–
MS remains in READY state until “READY
Timer” expires or GPRS Detach
PDU Transmission
STANDBY

January 2004
READY
STANDBY
–
MS known down to Routing Area by SGSN
–
MS attached to GPRS
–
May receive Packet paging
–
No data reception or transmission
F. Michaud – GPRS course
Page 8
Mobility Management
GPRS Attach
SMSC
BSC
MSC/VLR
HLR
3
5
1
2
GPRS handset 6
7
1. GPRS Attach Request
2. Authentication
3. Update Location (GPRS)
4. Insert Subscriber Data
5. Location Update (GSM)
6. GPRS Attach Accept
7. Attach complete
January 2004
4
2
DNS
SGSN
Charging
Gateway
GPRS
IP Backbone
Border
Gateway
GGSN
Inter PLMN
Backbone
ISP
External Network
F. Michaud – GPRS course
Page 9
Mobility Management
Routing Area Update
DNS
BSC
SGSN1
GPRS handset
5
BSC
4
3
2
GPRS
IP Backbone
SGSN2
GGSN
GPRS handset
1
8
6
7
1. RA Update Request (old RAI)
2. DNS Query: IP @ for old RAI
3. SGSN Context Request
4. SGSN Context Response
5. Forward Packets
6. Update PDP Context Request: IP @ of new RAI
7. Update PDP Context Response
8. RA Update Accept
January 2004
F. Michaud – GPRS course
Page 10
Session Management
Notion of QoS

QoS = Quality of Service

5 Classes as specified in ETSI
• Service Precedence / Priority
• Delay
• Mean Throughput
• Peak Througput
• Reliability

FTP (NRT):

Video Streaming (RT):
–
Service: minor
–
Service: medium
–
Delay: < 7 sec (most likely Best effort)
–
Delay: < 7 sec (most likely Best effort)
–
Mean throughput: 4.4 kbps
–
Mean throughput: 44 kbps
–
Peak throughput: N/A
–
Peak throughput: 64 kbps
–
Reliability: high to medium redundancy
–
Reliability: medium to low (UDP protocol)
January 2004
F. Michaud – GPRS course
Page 11
Session Management
Notion of PDP context


Packet Data Protocol context:
–
set of information stored in mobile, SGSN and GGSN
–
allow packet data transfer between a certain type of network and the mobile
PDP context contains:
January 2004
Main Field
Description
type of PDP network
IP, X25 ….
Mobile address
IP address or X.121 address for X25 network
SGSN address
IP address of the serving SGSN
NSAPI
Network Service Access Point
QoS Profile
Quality of service negociated for this PDP context
Access Point Name
APN (service) requested by the mobile (ie WAP, internet…)
F. Michaud – GPRS course
Page 12
Session Management
PDP Context Activation
SMSC
BSC
1
GPRS handset
MSC/VLR
HLR
2
DNS
Charging
Gateway
SGSN
5
GPRS
IP Backbone
1. Activate PDP Context Req
2. DNS Query
3. Create PDP Context Req
4. Create PDP Context Rsp
5. Activate PDP Context Ack
January 2004
Border
Gateway
Inter PLMN
Backbone
F. Michaud – GPRS course
3
4
GGSN
ISP
External Network
Page 13
Session Management
Data Transfer
SMSC
BSC
MSC/VLR
IP
SGSN
HLR
DNS
SNDCP
Charging
Gateway
GPRS handset
IP
GPRS
IP Backbone
Border
Gateway
GTP
IP
S-CDR
G-CDR
GGSN
IP
IP@ src
IP@ dst
Mobile
SGSN
Server
GGSN
January 2004
Inter PLMN
Backbone
F. Michaud – GPRS course
ISP
External Network
Page 14
Radio Resource Management
Notion of GPRS territory
TRX 1
TRX 2
CCCH
TCH
TCH
TCH
TCH
GSM
Territory
GPRS
Territory
TCH
Default
GPRS
Capacity
Dedicated
GPRS
Capacity
Territory border move based
On GSM and GPRS traffic load evolution
January 2004
F. Michaud – GPRS course
Page 15
Radio Resource Management
Physical Layer
TDMA frame=4,615 ms
01 2 3 4 5 6 7 01 2 3 4 5 6 7 01 2 3 4 5 6 7 01 2 3 4 5 6 7
1 GPRS multiframe = 52 TDMA frame=240 ms
Block 0 Block 1 Block 2 T Block 3 Block 4 Block 5 i Block 6 Block 7 Block 8 i Block 9 Block 10 Block 11 i
0
4
8
13
17
21
26
30
34
39
43
47
51
12 blocks of 4 radio burst each
Each block can transfer one GPRS logical channel information
January 2004
F. Michaud – GPRS course
Page 16
Radio Resource Management
Logical Signalling for GPRS
GPRS Air Interface Logical Channels
CCH
Common Channels
DCH
Dedicated Channels
PCCCH
Packet Common Control
Channels
(can be combined with CCCH)
BCH
Broadcast Channels
DOWNLINK ONLY
PBCCH
Packet Broadcast Control CH
(can be combined with BCCH)
MS CONTINUOUSLY
MONITORS
PPCH
Packet Paging CH
PAGCH
Packet Access Grant CH
PRACH
Packet Random Access CH
BSS WANTS TO
CONTACT MS
PDCH IS
ALLOCATED TO MS
MS ASKS FOR
PDCHs.
GPRS: DCH
'Dedicated' Channels
DCCH
Dedicated Control
Channels
PACCH
Packet Associated Control CH
Allocated to the opposite direction than the PDTCH
to which it is associated.
January 2004
F. Michaud – GPRS course
TCH
Traffic Channels
PTCCH
Packet Timing Control Channel.
PDTCH
Packet Data TCH, one channel can be shared
by several active users.
Page 17
Radio Resource Management
Timeslot sharing
GPRS data transfer = discontinuous series of Temporary Block Flows.

–
1 TBF = 1 user (with a given TFI, TLLI, USF)
–
1 TBF can be transferred onto several radio timeslots
TBF4
TBF3
TBF2
TBF2
TBF3
TBF1
TBF1
TBF1
TSL 0
TSL 1
TSL 2
TSL 3
TSL 4
TSL 5
TSL 6
TSL 7
BCCH
TCH
TCH
TCH
PDCH
PDCH
PDCH
PDCH
TDMA frame

Data transfer = Uplink / Downlink TBF (Temporary Block Flow) Assignment
–
Timeslots allocation GSM CCCH channels (RACH - AGCH - PCH) (GPRS - phase 1)
–
GPRS phase 2: dedicated common control channels (PBCCH/PCCCH)
January 2004
F. Michaud – GPRS course
Page 18
GPRS Part 2
Content
… to practice
IMPLEMENTATION CONSTRAINTS
NETWORK DIMENSIONING
NETWORK PLANNING
ANALYSIS AND OPTIMISATION
TOOLS FOR GPRS
January 2004
F. Michaud – GPRS course
Page 19
Implementation Constraints
Upgrade of GSM network

New Core Network
–
GPRS backbone is an IP network
• New approach in Mobile Telecommunication
• First interaction between IT and mobile telecom network dept.

Multi-supplier solution
–
Interoperability problems
• Interface Gb, Gs, Gr are standardised by ETSI but…

Immature specification leads to uncompatibility

Gb interface is very sensible
• Mobile / network compatibility over air interface

January 2004
PBCCH problem
F. Michaud – GPRS course
Page 20
Implementation Constraints
Software Releases

Release compatibility
–
–


Network is often heterogeneous

Different generation of base stations

Different switch and BSC
Release are delivered at different times
Incomplete GPRS features
–
QoS not implemented in first release
–
PBCCH not implemented in first release
immature ETSI specifications
–
January 2004
Suppliers follow different versions
F. Michaud – GPRS course
Page 21
Implementation Constraints
Heterogeneous BSS Network
GPRS Core
Network
South region - BSS Network
Supplier A
North region - BSS Network
Supplier B
GPRS handset
GPRS handset

Problem of uniform Quality of Service (different SW/HW, different problems)

Complex network evolution (i.e. new feature cannot be implemented country wide)
January 2004
F. Michaud – GPRS course
Page 22
Implementation Constraints
Handsets & Services

Limitation in mutlislot & coding scheme capability:
• First handsets: 2+1 (i.e. 2 TSL DL / 1 TSL UL)

24 kbps DL / 12 kbps UL
• Current handsets: 4+1


48 kbps DL / 12 kbps UL
ETSI specifications problems
• Lots of change request
• PBCCH not supported by network and first GPRS mobiles

Poor content for GPRS Services
• Lack of «adapted» phones
• Lack of «killer» applications
January 2004
F. Michaud – GPRS course
Page 23
GPRS Dimensioning
Number of GPRS users
Paquet transfer per users
Quality of Service
Coverage area
Peak hours
Network
Dimensioning
Transmission capacity
(Abis/Gb)
Bearer size
Number of PCU
Radio
Dimensioning
GPRS Territory size
Number of cells
TRX upgrade
Signalling increase
New hardware requirements
January 2004
F. Michaud – GPRS course
Page 24
Analysis and optimisation

Traffic analysis
GPRS Traffic on Microsoft/Orange stands(Hall 4) - ITU
Telecom 03
kbytes
100000
80000
60000
40000
20000
Max throughput DL
Ave throughput DL
Max throughput UL
Ave throughput UL
20
03
18
.1
0.
20
03
17
.1
0.
20
03
16
.1
0.
20
03
15
.1
0.
20
03
.1
0.
20
14
.1
0.
13
January 2004
Daily Volume UL
03
0
Daily Volume DL
kbits/sec
90
80
70
60
50
40
30
20
10
0
120000
F. Michaud – GPRS course
Page 26
Analysis and optimisation

Performance Analysis – Access to Network resource
1123
32.15
%
298
81.88
%
57.26
%
January 2004
F. Michaud – GPRS course
Page 27
Analysis and optimisation

Performance Analysis – Session success
13
%
2446
45.4%
623
87%
53.3
%
January 2004
F. Michaud – GPRS course
Page 28
Analysis and optimisation
Tools for GPRS

Probe System

Data capture across all GPRS network interfaces
MSC VLR
Gs
HLR
Gr
Gc
Gi
BTS
Gb
BSC
internet
Gn
SGSN
Gp
GGSN
BG
Foreign
PLNM
1. Data capture 2. Data data storage
January 2004
F. Michaud – GPRS course
3. Data analysis
Page 29
Analysis and optimisation
Tools for GPRS

Protocol analyser

January 2004
In depth signalling study
F. Michaud – GPRS course
Page 30
Documentation

Réseaux GSM (ISBN 2-7462-0153-4)


Ingénierie des réseaux cellulaires (ISBN 2-7462-0550-5)


Peter Stuckmann
GPRS Signalling & Protocol Analysis – Vol. 1

January 2004
Sami Tabbane
The GSM Evolution - Mobile Packet Data Services (ISBN 0-470-84855-3)


Xavier Lagrange, Philippe Godlewski, Sami Tabbane
Gunnar Heine
F. Michaud – GPRS course
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That’s all Folks!
January 2004
F. Michaud – GPRS course
Page 32