EWSD

1. Chapter1: EWSD EXCHANGE
 Structural Units Of EWSD Exchange
 DLU (Digital Line Unit)
 LTG (Line Trunk Group)
 SN (Switching Network)
 CP (Coordination Processor)
 Functional Units Of EWSD Exchange
 Control
 Switching
 Signaling
 Access
 Power
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).
Structural Units 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
Modules of Digital Line Unit
Digital
Line
Unit
Processor
and
Controller
Interface
Subscriber
line circuit
(SLC)
Power
BDCG
RGMG
DLUC
DCC-CR
DIU
BDB
BDE
Testing
SLMACOS
SLMACMRL
SLMAITF
SLMD
FMTU
LCMM

3. 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.
Physical Rack Diagram of DLU (IBA 1-A):
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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.
FUNCTIONS OF LTG

5. 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:
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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.
Line
Trunk
Group
Interfacing
Trunk
Signaling
Memory
Unit
Tone
Generator
Code
Receiving
Sync
&
Switchin
g
Module
Power
CRP
4 x DIU’s
TOG
PMUB
PMUC
PMUD
GSL
DCC-DE
SILC-B
SILC-C
CGS
M

6. 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)
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
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:
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7. 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:
 Base Processors
 Call Processors
 Input / Output Control
 Bus for Common Memory
 Common Memory
 Input / Output Processors
CoordinationProcessor 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:
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).

8. Functionality of CP
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
COORDINATION
PROCESSOR
BASE
PROCESSOR
CALL
PROCESSOR
INPUT/OUTPUT
PROCESSOR
COMMON
MEMORY
BUS FOR
COMMON
MEMORY
INPUT/OUTPUT
CONTROL

9.  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
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.
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

10.  Very reliable signal transmission
 Flexibility to adapt to future requirements
Suitable transmission Medium
 Copper Wires
 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.