Table of Contents

1. EWSD (Eidal Widal Switch Digital).....................................................1A. Parts of EWSD Switch........................................................................1B. DLU (Digital line unit):.......................................................................1

i. Functions Of DLU..................................................................2ii. Modules of Digital Line Unit.............................................3

iii. Physical Rack Diagram Of DLU (IBA 1-A):..................4C. Line Trunk Group (LTG)....................................................................5

i. Physical Rack Diagram:......................................................5ii. Functions of LTG...................................................................7

D. Switching Network (SN)....................................................................8i. Functions OF Switching Network:.................................8

ii. Structure:.................................................................................9iii. Physical Rack Diagram:......................................................9

E. Coordination Processor:..................................................................10i. Coordination Processor Modules..................................10

ii. Functionality of CP.............................................................112. Functional Units of EWSD exchange:..............................................12

F. Control....................................................................................................12i. Message Buffer.....................................................................12

ii. Central Clock Generator..................................................13iii. Control System Panel.........................................................13

G. Switching...............................................................................................14H. Signaling................................................................................................14I. Access......................................................................................................15

3. ZTE Exchange............................................................................................16J. Functions of Modules.......................................................................19

4. PRI Exchange.............................................................................................215. Common Channel Signaling 7.............................................................22

EWSD (Eidal Widal Switch Digital)

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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 SwitchEWSD 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).

Functions Of DLU

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Modules of Digital Line Unit

1- Subscriber Line Module (SLM)

Digital Line Unit

Processor and

Controller

Interface

Subscriber line circuit

(SLC)

Power

BDCGRGMGDLUC

DCC-CR DIUBDBBDE

Testing

SLMACOSSLMACMRLSLMAITFSLMD

FMTU

LCMM

2

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.

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Physical Rack Diagram Of DLU (IBA 1-A):

DCC

SLM

SLM

SLM

SLM

SLM

SLM

SLM

SLM

RGMG

BDB

BDCG

DLUC

DIU

FMTU

LCMM

SLM

DCC

DCC

SLM

SLM

SLM

SLM

SLM

SLM

SLM

SLM

RGMG

BDB

BDCG

DLUC

DIU

SLM

SLM

SLM

SLM

DCC

DCC

SLM

SLM

SLM

SLM

SLM

SLM

SLM

SLM

BDE

BDE

SLM

SLM

SLM

SLM

SLM

SLM

SLM

SLM

DCC

DCC

SLM

SLM

SLM

SLM

SLM

SLM

SLM

SLM

BDE

BDE

SLM

SLM

SLM

SLM

SLM

SLM

SLM

SLM

DCC

DCC

SLM

SLM

SLM

SLM

SLM

SLM

SLM

SLM

BDE

BDE

SLM

SLM

SLM

SLM

SLM

SLM

SLM

SLM

DCC

DCC

SLM

SLM

SLM

SLM

SLM

SLM

SLM

SLM

BDE

BDE

SLM

SLM

SLM

SLM

SLM

SLM

SLM

SLM

DCC

DCC

SLM

SLM

SLM

SLM

SLM

SLM

SLM

SLM

BDE

BDE

SLM

SLM

SLM

SLM

SLM

SLM

SLM

SLM

DCC

DCC

SLM

SLM

SLM

SLM

SLM

SLM

SLM

SLM

BDE

BDE

SLM

SLM

SLM

SLM

SLM

SLM

SLM

SLM

DCC

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

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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:

DIU

DIU

DIU

DIU

CRP

TOG

GSL

CGSM

PMU

SILC

DCC

LTG-B

The LTGB is used for connecting:

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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)

Functions of LTG

6

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).

Line Trunk Group

Interfacing

Trunk

Signaling

Memory Unit

Tone Generator

Code Receiving

Sync &SwitchingModule

Power

CRP

4 x DIU’s

TOG

PMUBPMUCPMUD

GSL

DCC-DE

SILC-BSILC-C

CGSM

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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

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)

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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:

TSM

TSM

TSM

TSM

LIS

LIS

SGC

LIS

LIS

TSM

TSM

TSM

TSM

DCC

TSM

TSM

TSM

TSM

LIS

LIS

SGC

LIS

LIS

TSM

TSM

TSM

TSM

DCC

Coordination Processor:

The CP performs the following functions in a network node:

Call processing

Operation and maintenance

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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).

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:

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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

COORDINATION PROCESSOR

BASE PROCESSOR

CALL PROCESSOR

INPUT/OUTPUT PROCESSOR

COMMON MEMORY

BUS FOR COMMON MEMORY

INPUT/OUTPUT CONTROL

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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

ControlControl 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

LTGs and the common channel signaling network control

(CCNC):Orders

Message Buffer Group

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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 GeneratorIn 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 PanelThe 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. 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.

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SwitchingBy 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).

SignalingThe 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

Optical Fibers

Digital Radio Links

Satellite links

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AccessThis 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.

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.

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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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SCL: Subscriber line circuit.DSPU: TSLC: Test subscriber line currentDT: Digital trunksCOMA: Communication card.MPPP: COMMUNICATION CARD.NET: Switching networkCKG: Clock generation.

10

ALARM-48+5-5

ALARM-48+5

-5

DSPU

DSPU

DSPU

DSPU

PP

TSLC

TSLC

TSLC

TSLC

MasterStandbyOfflineAlarmPower

SwitchResetOn/off

MasterStandbyOfflineAlarmPower

DT

DT

DT

DT

DT

10

10

ALARM-48+5

-5

SwitchResetOn/off

ALARM-48+5-5

10

DSPU

DSPU

COMA

COMA

MPPP

MPPP

SLC

SLC

SLC

SLC

SLC

SLC

PP

PP

SLC

SLC

SLC

SLC

SLC

SLC

SLC

SLC

SLC

SLC

SLC

SLC

SLC

SLC

SLC

SLC

SLC

SLC

SLC

ZTE ZXJ10 MODULE

CKG

NET

CKG

NET

17

AnalogSubscriber

DigitalSubscriber

VSX

TrunkSubscriber

Centrex

BSC

BSC

BSC

PSM(PHM)

PSM(RSM)

MSS

SNM

NT SERVER

SNM (CTL)

MSMCTL

RSU

Optic fiber4.8 Mb/s

8 M b/s Optic fiber

Terminal group

OMM

CSM

WORKING OF ZTE EXCHANGE

ZXJ10

18

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 ModulesOMM (operation and maintenance module):

1- Global traffic handling.2- Database management and modification.3- Man-machine interface.4- Billing handling centre.5- Maintenance, diagnosis and test.6- 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.

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PRI ExchangePRI 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.

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.

USER TelephoneExchange

I N

PRI ISPTransit Exchange

Connection establishment in PRI

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