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Table of Contents
1. EWSD (Eidal Widal Switch Digital) ............................................................ 1
A. Parts of EWSD Switch ............................................................................. 1
B. DLU (Digital line unit): ........................................................................... 1
i.
Functions Of DLU ..................................................................... 2
ii.
Modules of Digital Line Unit................................................... 3
iii. Physical Rack Diagram Of DLU (IBA 1-A): .......................... 4
C. Line Trunk Group (LTG) ........................................................................ 5
i.
Physical Rack Diagram: ........................................................... 5
ii.
Functions of LTG ....................................................................... 7
D. Switching Network (SN) ......................................................................... 8
i.
Functions OF Switching Network: ......................................... 8
ii.
Structure: .................................................................................... 9
iii. Physical Rack Diagram: ........................................................... 9
E. Coordination Processor: ........................................................................ 10
i.
Coordination Processor Modules ......................................... 10
ii.
Functionality of CP ................................................................. 11
2. Functional Units of EWSD exchange: ....................................................... 12
F. Control ..................................................................................................... 12
i.
Message Buffer ........................................................................ 12
ii.
Central Clock Generator ........................................................ 13
iii. Control System Panel ............................................................. 13
G. Switching ................................................................................................. 14
H. Signaling .................................................................................................. 14
I. Access....................................................................................................... 15
3. ZTE Exchange ............................................................................................... 16
J. Functions of Modules ............................................................................ 19
4. PRI Exchange ................................................................................................ 21
5. Common Channel Signaling 7 ....................Error! Bookmark not defined.
1
EWSD (Eidal Widal Switch Digital)
EWSD is the digital exchange made by German Company Siemens. This is
the very reliable exchange which is mostly used in Pakistan.
This type of digital exchange is used as local, tandem, transit as well as
international gate way exchange.
The most common switch is used as main exchange. This can operate as
PSTN, ISDN (BRI), PRI, CMMERCIAL Subscriber (Pay phones).
Parts of EWSD Switch
EWSD switch can be divided into following parts.




Digital line unit (DLU).
Line trunk group (LTG).
Switching network (SN).
Coordination processor (CP).
DLU (Digital line unit)
 DLU provides the gateway to the EWSD exchange.
 The data of home and commercial subscribers are stored in specific
modules in DLU.
 The telephone ring is generated in DLU.
 The metering of voltage is done in DLU.
 Provides contact with DIU (digital interface unit).
2
Functions Of DLU
FMTU
Processor
and
Controller
Testing
LCMM
BDCG
RGMG
DLUC
Digital
Line Unit
Interface
Power
DCC-CR
Subscriber
line circuit
(SLC)
SLMACOS
SLMACMRL
SLMAITF
SLMD
DIU
BDB
BDE
3
Modules of Digital Line Unit
1- Subscriber Line Module (SLM)
SLM modules store the data of all types of subscribers that includes PSTN,
ISDN, PRI, home users and commercial users. In IBA1-A there are two
types of SLM modules
 SLMA COS.
 SLMA CMRL.
The SLMA COS module supports 8 subscriber telephone lines and
connects them to the exchange.
The SLMA CMRL module supports 6 commercial lines i.e. public call
offices and connects them to main exchange.
2- Bus Distribution Base(BDB)
The BDB module controls all the buses that are running throughout the
DLU. The BDB modules are present in the first frame and they monitor the
sub control units BDE’S that are control units of the bus in the other frames.
3- Bus Distribution Extension(BDE)
The BDE modules are control units of different shelves of a single rack
of the EWSD exchange. The BDE module is controlled by BDB.
4- Ring Generation and Measuring Module (RGMG)
The RGMG module generates ring and it also acts as metering unit for
voltage in the digital line unit.
5- Digital line Unit Control (DLUC):
The DLUC module is the main control module in the DLU .it monitors
all the functionalities of different modules of the DLU.
6- Bus Distribution Clock Generation (BDCG):
This module generates the clock for bus distribution so that all the buses
are synchronized.
7- DCC:
One DCC module provides the voltage to first eight modules of a shelf
and the later eight modules are supported by an other DCC module at the
end of the shelf.
4
Physical Rack Diagram Of DLU (IBA 1-A):
D S S S S S S S S R
C L L L L L L L L G
C M M M M M M M M M
G
D S S S S S S S S R
C L L L L L L L L G
C M M M M M M M M M
G
D S S S S S S S S B
C L L L L L L L L D
C M M M M M M M M E
B B
D D
B C
G
B B
D D
B C
G
B S
D L
E M
D
L
U
C
D
L
U
C
S
L
M
D
I
U
D S S S S S S S S B
C L L L L L L L L D
C M M M M M M M M E
B S S S S S S S S D
D L L L L L L L L C
E M M M M M M M M C
D S S S S S S S S B
C L L L L L L L L D
C M M M M M M M M E
B S S S S S S S S D
D L L L L L L L L C
E M M M M M M M M C
D S S S S S S S S B
C L L L L L L L L D
C M M M M M M M M E
B S S S S S S S S D
D L L L L L L L L C
E M M M M M M M M C
D S S S S S S S S B
C L L L L L L L L D
C M M M M M M M M E
B S S S S S S S S D
D L L L L L L L L C
E M M M M M M M M C
D S S S S S S S S B
C L L L L L L L L D
C M M M M M M M M E
B S S S S S S S S D
D L L L L L L L L C
E M M M M M M M M C
D
I
U
F
M
T
U
S
L
M
L
S
C
L
M
M
M
S S
S
L L
L
M M
M
D
C
C
D
C
C
S S S S S S D
L L L L L L C
M M M M M M C
5
Line Trunk Group (LTG)
The line/trunk group (LTG) forms the interface between the digital
environment of the node and the digital switching network (SN). The LTGs
perform non-central control functions and thus relieve the coordination
processor (CP) of routine work.
Functions of LTG:
Following are the major functions of LTG
 LTG provides direct connection of one exchange with the other
exchanges of the same city or the other cities.
 LTG generates telephone tone.
 LTG provides a gateway to the switching network.
 LTG provides interface between DLU and PCM.
Several LTG types are available for optimal implementation of the various
line types and signaling methods. The two main types of LTGs (differing in
their functionality) used are:
 LTG-B
 LTG-C
Physical Rack Diagram:
D
I
U
D
I
U
D
I
U
D
I
U
C
R
P
T
O
G
G
S
L
C
G
S
M
P
M
U
S
I
L
C
D
C
C
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LTG-B
The LTGB is used for connecting:
 Up to four digital transmission routes (PDCs) for DLUs at
transmission rates of 2048 kbit/s
 Up to four primary rate accesses (PAs) for medium-sized and large
ISDN PABXs (ISDN subscribers with PA) at a transmission rate of
2048 kbit/s.
 Main Components of an LTG-B
 Group processor (GP)
 Link interface unit between line/trunk group and switching
network (LIU)
 Group switch (GS)
 Speech multiplexer (SPMXA)
 Signaling unit (SU)
 Line/trunk unit (LTU)
7
Functions of LTG
4 x DIU’s
Interfacing
SILC-B
SILC-C
CGS
M
Trunk
Sync
&
Switchin
g
Module
DCC-DE
Code
Receiving
Line Trunk
Group
Power
Signaling
GSL
CRP
Tone
Generator
Memory
Unit
PMUB
PMUC
PMUD
TOG
8
Switching Network (SN)
By virtue of its high data transmission quality, the switching network can
switch connections for various types of service (for example telephony,
facsimile, teletext, data transmission).
This means that switching network is also ready for the Integrated
Services Digital Network (ISDN).
Functions OF Switching Network:
 Duplicated (full redundancy)
 Highly-Integrated switching network modules
 One space stage module can handle up to 1024 simultaneous calls
with full redundancy
 Interfaces of 8,192 Kb/s available within
 Highly compact design from space-saving point of view
 An exchange of 10,000 subscribers may accommodate the SN in a
single rack
 Two kinds of connections: Switched & Semi-permanent
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Structure:
In large and very large exchanges the capacity stages of the switching
network (SN:504LTG, SN:252LTG and SN:126LTG) include
 One time stage incoming (TSI)
 Three space stages (SS)

One time stage outgoing (TSO)
Medium-sized and small exchanges (SN:63LTG and SN:15LTG) contain
 One time stage incoming (TSI)

One space stage (SS)
 One time stage outgoing (TSO)
Physical Rack Diagram:
T T T T L L
S S S S I I
M M M M S S
S L L T T T T D
G I I S S S S C
C S S M M M M C
T T T T L L
S S S S I I
M M M M S S
S L L T T T T D
G I I S S S S C
C S S M M M M C
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Coordination Processor:
The CP performs the following functions in a network node:
 Call processing
 Operation and maintenance
 Safeguarding
The CP consists of the following processors:
o Base Processors
o Call Processors
o Input / Output Control
o Bus for Common Memory
o Common Memory
o Input / Output Processors
Coordination Processor Modules
1. BAP:
The BAPMs and the BAPSs provide the same software functional units.
2. CAP:
The CAPs mainly include software for call processing functions.
3. IOC:
IOCs have only firmware for communication with the call processing,
O&M and data communication peripheries.
4. BCMY:
The bus for common memory (BCMY) connects all processors (BAP,
CAP), including the input/output controls (IOC), with each other and
with the common memory (CMY).
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5. CMY:
The common memory (CMY) includes, among other things, the common
database for all processors, plus the input and output lists for the IOP.
The
CMY is duplicated in order to ensure a high level of
availability.
6. IOP:
Different types of input/output processors (IOP) connect the CP113D
with
other units in the network node, the external bulk memories, the
operation
and maintenance terminal, the operation and maintenance
center (OMC, via
data lines) and computer centers (also via data
lines).
Functionality of CP
BASE
PROCESSOR
COMMON
MEMORY
BUS FOR
COMMON
MEMORY
INPUT/OUTPUT
CONTROL
COORDINATION
PROCESSOR
CALL
PROCESSOR
INPUT/OUTPUT
PROCESSOR
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Functional Units of EWSD exchange:
The EWSD system is divided into different functional areas called
subsystems coordinated by a central system. Following are the main
functional units of EWSD exchange.
1. Control
2. Switching
3. Signaling
4. Access
5. Power
Control
Control belongs to the area which is responsible for the coordination of the
various subunits. Control consists of the following:




Coordination Processor (CP)
Message Buffer (MB)
System Panel (SYP)
Central Clock Generator (CCG)
Message Buffer
The task of MB is to control the exchange of messages between the
following subsystems:
 Coordination Processor (CP) and line/trunk groups (LTG):
Commands and Messages
 CP and switch group controls (SGC) of the switching
network: Setting commands for the SN
 LTGs among one another: Reports
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
LTGs and the common channel signaling network control
(CCNC):Orders
Message Buffer Group
The message buffer is divided into functional groups called Message
Buffer Groups according to the expansion concept. One message buffer
group consists of one message buffer unit for Switch Group Control and two
message buffer units for LTG.
In the least configuration, at least one message buffer group may exist with
at least one MBUL and one MBUS active where as the other MBUL may be
inactive.
In the highest configuration, there are up to 4 message buffer groups with 4
MBUS and 8 MBUL.
Central Clock Generator
In order to switch and transmit digital information, the sequence of
operations must be synchronous throughout the equipment involved.
This requires a clock supply with a high level of reliability, precision and
consistency for all the nodes in the digital network.
This task is fulfilled by the central clock generator (CCG).
Depending upon the accuracy required, the following two modes of
operation are possible.
Control
System Panel
The purpose of the system panel is to display alarms and advisories of
internal and external supervisory units outside the system) both visually and
acoustically.
It is divided into two parts namely the System Panel Control and the System
Panel Display unit.
System Panel Control:
This utilizes the free space in the Message Buffer Rack. It is connected with
the IOP: MB in the CP113.
Although itself it is not redundant, it has a redundant connection with the CP
via two IOP: MBs, each belonging to a different side.
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The system panel display unit is connected with the control (SYP) via a
cable but can be placed at any suitable place within the exchange by direct
connection or in an OMC using some transmission system.
This unit is responsible to display alarms and advisories of internal and
external supervisory units (outside the system) both visually and
acoustically. It is also responsible to show the CP load (in ERL) and the
current date and time of the system.
Switching
By virtue of its high data transmission quality, the switching network can
switch connections for various types of service (for example telephony,
facsimile, teletext, data transmission).
This means that switching network is also ready for the Integrated
Services Digital Network (ISDN).
Signaling
The EWSD digital electronic switching system can control connections to
and from other network nodes using all the common signaling systems.
The signaling functions in a EWSD network-node are handled by the
"common channel signaling network control (CCNC)".
One system that is particularly suitable for stored-program-controlled digital
nodes is signaling system no. 7.
This transports signaling information separately from the user information
(voice, data) on common-channel signaling links.
Advantages: Higher speed signaling
 Very reliable signal transmission
 Flexibility to adapt to future requirements
Suitable transmission Medium
 Copper Wires
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 Optical Fibers
 Digital Radio Links
 Satellite links
Access
This includes:
 Line / Trunk Group (LTG)
 Digital Line Unit (DLU)
 Digital Announcement System (DAS).
DAS explained:
The digital announcement unit announces recorded messages to the
subscriber relating to different matters such as reason for disconnection or
the disability of a non STD phone to dial an outstation call. The necessary
information for such an announcement is provided by CP and DLU.
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ZTE Exchange
ZTE is a Chinese telecommunication company that was founded in
1985.Initially it had its network limited in different cities of China later on
ZTE extended its network to different countries of Asia and Africa.
Unlike EWSD, ZTE is modular based exchange and in each module we have
its own control system, switching network and signaling network.
At IBA exchange a ZTE exchange named ZXJ10 is installed. It has
capability of supporting 10000 lines. A detailed diagram of ZTE’s module
is shown in the next page.
The main advantage of having a ZTE exchange is its low cost. The ZTE
exchange costs almost eight times less than that of Siemens, Ericsson or
Alcatel. That is the reason why ZTE is becoming so popular in the
developing and poor countries of Asia and Africa.
The disadvantage of ZTE exchange is that it is not as reliable as EWSD,
Ericsson, Alcatel or even Huawei .ZTE exchange suffers from more errors
than other exchanges.
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ZTE
1
0




D
S
P
U
ALAR
M
D
S
P
U
ZXJ10 MODULE
D
P T
D



1
0




D
T
D
T
C
O
M
A
C
O
M
A
P
S
L
C
T
S
L
C
T
S
L
C
T
S
L
C
+5
-5
D
T
D
T
D
T
Master
Standby
Offline
Alarm
Power
ALAR
M
Switch
Reset
On/off
-48
+5
-5
C
K
G
D
S
P
U
ALAR
M
D
S
P
U
M
P
P
P
M
P
P
P
Master
Standby
Offline
Alarm
Power
Switch
Reset
On/off
N
E
T
S
L
C
S
L
C
S
L
C
S
L
C
S
L
C
S
L
C
S
L
C
S
L
C
-48
+5
-5
1
0





S
P
U
-48
1
0

S
P
U
S
L
C
S
L
C
S
L
C
S
L
C
S
L
C
S
L
C
S
L
C
S
L
C
S
L
C
P
P
S
L
C
N
E
T
P
P
S
L
C
C
K
G
S
L
C
S
L
C
S
L
C
ALARM
-48
+5
-5
S
L
C
S
L
C
SCL: Subscriber line circuit.
DSPU:
TSLC: Test subscriber line current
DT: Digital trunks
COMA: Communication card.
MPPP: COMMUNICATION CARD.
NET: Switching network
CKG: Clock generation.
S
L
C
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WORKING OF ZTE EXCHANGE
ZXJ10
RSU
Optic fiber
4.8 Mb/s
Analog
Subscriber
8 M b/s
Optic fiber
PSM
(PHM)
MSM
CTL
S
N
M
Digital
Subscriber
VSX
PSM
(RSM)
SNM (CTL)
Trunk
Subscriber
CSM
Centrex
BSC
NT SERVER
OMM
BSC
BSC
M
S
S
Terminal
group
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OMM: Operation and maintenance module.
MSM: Message switching module.
PSM: Peripheral switching module.
RSM: Remote switching module.
DSN: Digital switching network.
CSM: Central switching module.
Functions of Modules
OMM (operation and maintenance module):
123456-
Global traffic handling.
Database management and modification.
Man-machine interface.
Billing handling centre.
Maintenance, diagnosis and test.
Supervising the system operation status and the remote operation
environment.
CSM (centre switching module):
One is the voice channel switching control part(SNM) and the other is
message switching control part(MSM)
SNM:
Its main task is to complete the voice channel switching . the DSN consists
of several planes,each two planes of 8k form a pair of active/standby DSN
switching network that can be configured with 8 such 8k planes at
maximum to constitute a switching network of 64k *64k.
MSMCTL:
It mainly provides the message switching for each MP status (module
processor), to realize the communication between OMM and each MP.
While man machine commands are send to each MP via MSMCTL, such as
the MP switch over command, etc.
PERIPHERAL SWITCHING MODULE (PSM):
Its main functions are as follows.
1- PSTN subscriber access and intra-office traffic handling.
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2- ISDN subscriber access.
3- Centrex commercial users’ access.
4- Mobile subscriber’s access.
A single PSM can constitute a single module office.
REMOTE SWITCHING MODULE (RSM):
Its structure is similar to PSM. Its functions are:
1- Providing access to remote users.
2- Realizing intra subscribers switching.
3- Realizing central networking with CSM.
4- Providing the same n * 64 kb/s (n<=128) dynamic time slots
switching as PSM.
RSU:
1- It mainly provides access for small group of remote subscribers which
are usually POTS users.
2- Realizing intra RSU traffic handling.
3- Networking with CSM, realizing the whole network calling possible
located far from central office by using the low optic fiber
connections.
21
PRI Exchange
PRI stands for primary rate interface. The PRI exchange connects the ISP’s
and the subscribers of the telephone line.
C&C08 is the PRI exchange installed at IBA. It is manufactured by Chinese
company Huawei.
USER
Telephone
Exchange
Transit
Exchange
PRI
IN
Connection establishment in PRI
The line provided to ISP can support data transport at the rate of 2 Mbps and
cannot exceed this limit. Each card in this Huawei exchange has 16 PRIs .
Each PRI has 32 channels,30 channels are allocated for 2 way
communication of digital data between the server and the internet users, one
channel is utilized for frame alignment (synchronization) and one is used to
signal the communication data. There are CPC link cards, STP and SRC
announcement cards. The interconnection between different cards and
frames is through optical fiber.
ISP
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