CONTENTS

CERTIFICATE I

ACKNOWLEDGEMENT II

ABSTRACT III

1. EWSD SYSTEM OVERVIEW 2

2. DIGITAL LINE UNIT 14 2.1. Introduction

2.2. Structure

3. LINE TRUNK GROUP 21 3.1. Introduction

3.2. Connections 3.3. Group Processor Software

4. SWITCHING NETWORK 32

4.1. Introduction 4.2. General Features 4.3. Position and Functional Structure 4.4. Capacity Stages 4.5. Functional Units of SN

5. MESSAGE BUFFER 40 5.1 Introduction 5.2 Structure

6. COORDINATION PROCESSOR 48 6.1 Introduction 6.2 Structure 6.3 Functions

7. REPORT 58

1

EWSD – SYSTEM OVERVIEW

INTRODUCTION:

After years of being treated as a luxury, telecommunication has come into its own in the

English Plan. The Department of Telecommunications has announced ambitious plans for

the addition of 7.5 million lines to the existing 5.8 million by the end of the 8th plan (1992-

97) as compared to only 3.2 million in 1982-92.

To bridge the gap between the supply and demand DoT invited a tender for 200,000 lines

of digital switching equipment on Rupee payment. In the industrial policy of July 1991

telecom equipment was delicensed and thrown open to foreign investments. These foreign

suppliers set up their validation exchanges, each of 10,000 lines capacity (including two

RSUs of 2K each), at different places, e.g. EWSD of Siemens (Germany) at Calcutta,

AXE-10 of Ericsson (Sweden) at Madras, Fetex-150 of Fujitsu (Japan) at Bombay, OCB-

283 of Alcatel (France) at Delhi etc.

Three new Digital Switching Systems, i.e., EWSD, AXES-10 Fetex-150, which got

validated first, were inducted in the Indian Telecom. Network & three lakh lines were

imported from these suppliers. In addition 3.50 lakh lines were also imported on lease basis

from these suppliers. Subsequently four more switches, i.e., OCB-283 of Alcate (France),

5ESS of AT&T (USA), System-X of GPT (UK) and NEAX-61E of NEC (Japan) also got

validated.

System Features:

EWSD Digital switching system has been designed and manufactured by M/s Siemens,

Germany. The name is the abbreviated from of German equivalent of Electronic Switching

System Digital (Electronics Wheler Systeme Digitale). EWSD switch can support

maximum 2,50,000 subscribers or 60,000 incoming, outgoing or both way trunks, when

working as a pure tandem exchange. It can carry 25,200 Erlang traffic and can withstand

2

1.4 million BHCA. It can work as local cum transit exchange and has CCS No.7, ISDN and

IN capabilities.

System Architecture:

The main hardware units of an EWSD switch are as under:

- Digital line unit (DLU) – functional unit on which subscriber lines

terminated.

- Line/Trunk Group (LTG) – Digital Trunks DLUs are connected to LTGs.

The access function determined by the network environment

is handled by DLUs and LTGs.

- Switching Network (SN) - All the LTGs are connected to the SN which

interconnects the line and trunks connected to the exchange in according

with the call requirement of the subscribers. CCNC and CP are also

connected to SN.

- Coordination Processor (CP) - It is used for system-wide coordination

functions, such as, routing, zoning, etc. However each subsystem in EWSD

carryout practically all the tasks arising in their area independently.

- Common Channel Signaling Network Control (CCNC) Unit – This unit

functions as the Message Transfer Part (MTP) of CCS-7. The User Part

(UP) is incorporated in the respective LTGs.

Block diagram of EWSD is given in Figure 1. It also shows that the most important

controls are distributed throughout the system. This distributed control reduces the

coordination overheads and the necessity of communication between the processors. It

results in high dynamic performance standard.

3

For inter-processor communications, 64 kbps semipermanent connections are set through

SN. This avoids the necessity for a separate interprocessor network.

1.Digital Line Unit (DLU):

Analog or Digital (ISDN) subscribers or PBX lines are terminated on DLU .DLU s can be

used locally within the exchange or remotely as remote switch unit, in the vicinity of

groups of subscribers.

DLUs are connected to EWSD sub-systems via a uniform interface standardized by

CCITT, i.e., Primary Digital Carrier (PDC) to facilitate Local or Remote installation. A

subset of CCS# 7 is used for CCS on the PDCs.

One DLU is connected to two different LTGs for the reasons of security (Figure 2). A local

DLU is connected to two LTGs via two 4 Mbps (64 TSs) links, each towards a different

DLU

DLUC

LTG

GP

LTG

GP

COMMON CHANNEL SIGNALING

CCNC

CCNP

ACCESS

COORDINATION

CPSYPSYPC

MBMBC

CCG

EM

OMTSGC

SWITCHING NETWORK

Figure 1. DISTRIBUTED CONTROLS IN EWSD

4

LTG. In case of remote DLUs maximum 4 PDCs of 2 Mbps (32 TSs) are used per DLU,

two towards each LTG. Hence total 124 channels are available between a DLU and the two

LTGs, out of which 120 channels are used for user information (speech or data) and

signaling information is carried in TS16 of PDC0 and PDC2.

Within the DLU, the analog subscribers are terminated on SLMA (Subscriber Line Module

Analog) cards (module). Similarly Digital (ISDN) subscribers are terminated on the SLMD

modules. Each module can support 8 SLCAs (Subscribers Line Circuit Analog) and one

SLMP (Subscribers Line Module Circuit Processor).

One DLU can carry traffic of 100 Erlangs. A standard rack of DLU (local or remote) can

accommodate one DLU of 944 subscribers of two DLUs of 432 subscribers each. Smaller

racks (Shelter) are also available for remote DLUs in which lesser number of subscribers

can be equipped.

In case the link between a remote DLU and the main exchange is broken, the subscribers

connected to the remote DLU can still dial each other but metering will not be possible in

this case. For emergency service DLU-controller (DLUC) always contain up-to-date

subscribers data. Stand Alone Service Controller card (SASC) is provided in each R-DLU

for switching calls in such cases. This card is also used interconnecting a number of

remotely situated DLUs (Maximum 6), in a cluster, called a Remote Control Unit (RCU),

so that subscribers connected to these remote DLUs can also talk to each other in case the

link of more then one DLU to the main exchange is broken. An EMSP module (Emergency

Service equipment for Push-button subscribers) is used to make internal calls by DTMF

subscribers when the remote DLU link is broken.

5

All DLUs are provided with a Test Unit (TU) for performing tests and measurements on

SLCAs, subscribers lines and telephones. An ALEX (Alarm EXternal) module is used for

forwarding external alarms, i.e., fire, temperature, etc, to System Control Panel (SYP).

2.Line/Trunk Groups

The line/trunk groups (LTG) from the interface between the digital environment of an

EWSD exchange and the switching network (SN). The LTGs are connected in any of the

following ways:

I. Via 2/4 Mbps PDCs with remote/local DLUs to which analogue or ISDN

subscribers are connected.

PDC3 w/o CCS

PDC2 WITH CCS

PDC1 W/O CCS

PDC0 WITH CCS

SUBSCRIBER LINES AND PBX LINES FOR SMALL AND MEDIUM SIZED PBXS REMOTE

APPLICATION

LOCAL APPLICATION

4Mbps

SNLTG

LTG

CP

4 MbpsDLU

DLU

SUBSCRIBER LINES AND PBX LINES FOR SMALL AND MEDIUM SIZED PBXS

c

rrrrr

APPLICATIONS AND CONNECTION OF DIGITAL LINE UNITFigure 2

6

II. Via 2 Mbps Digital access lines to other digital exchanges in the network, or Via

Signal Converter-Multiplexer (SC-MUX) to analog trunks from analog exchanges

in the network. SC-MUX do not from the part of the EWSD exchange equipment

III. Via Primary rate Access lines to ISDN PBXs (ISDN subscribers with PA)

Functions

The primary functions of the LTG art as follows:

(i) Call processing functions, i.e., receiving and analyzing line and register signals,

injecting audible tones, switching user channels from and to the switching

network, etc.

(ii) Safeguarding functions i.e., detecting errors in the LTG and on transmission

paths within the LTG, analyzing the extent of errors and initiating counter

measures such as disabling channels or lines, etc.

(iii) Operation and maintenance functions, i.e., acquiring traffic data, carrying out

quality-of-service measurements, etc.

Although the subscriber lines and trunks employ different signaling systems, the LTGs

present signaling-independent interface to the switching network. This facilitates the

following:

- flexible introduction of additional or modified signaling procedures,

- a signaling-independent software system in the CP for all applications.

The bit rate on all highways linking the line/trunk groups and the switching network is

8192 Kbps (8 Mbps). Each 8 Mbps highway contains 128 channels at 64 Kbps each. Each

LTG is connected to both planes of the duplicated switching network.

7

3.Switching Network

Digital peripheral units of EWSD, i.e., LTGs, CCNC, MB are connected to the Switching

Network (SN) via 8192 kbps highways called SDCs (Secondary Digital Carriers), which

have 128 channels each. The SN consists of several duplicated Time Stage Groups (TSG)

and Space Stage Groups (SSG) housed in separate racks. Connection paths through the

TSGs and SSG are switched by the Switch Group Controls (SGC) provide in each TSG and

SSG, in accordance with the switching information from the coordination processor (CP).

The SGCs also independently generate the setting data and set the message channels for

exchange of data between the distributed controls.

3.1.Coordination Area

3.1.1.Coordination Processor

The coordination processor (CP) handles the data base as well as configuration and

coordination functions, e.g.:

Storage and administration of all programs, exchange and subscriber data,

Processing of received information for routing , path selection, zoning, charges,

Communication with operation and maintenance centers,

Supervision of all subsystems, receipt of error messages, analysis of supervisory

result messages, alarm treatment, error detection, error location and error

neutralization and configuration functions.

Handling of the man-machine interface.

CP 113 is used in medium-sized to very large exchanges. The CP113 is multiprocessor and

can be expanded in stages. It has a maximum call handling capacity of over 1,00,000

BHCA. In the CP113, two or more identical processors operate in parallel with load

sharing. The rated load of n processors is distributed among n+ 1 processor. This means

that if one processor fails, operation can continue without restriction (redundancy mode

with n+ 1 processor.

8

The other functional units of CP 113 are call processors (CAP) which deal only with call

processing functions. Hardware wise they are similar to BAPs and form a redundant pool

together with BAPs.

3.1.2 Other units assigned to CP are:

Message Buffer (MB) for coordinating internal message traffic between the CP, the

SN, the LTGs and the CCNC in an exchange.

Central Clock Generator (CCG) for the synchronization of the exchange and, where

necessary, the network. The CCG is extremely accurate (10^9). It can, however, be

synchronized even more accurately by an external clock (10^11). MBs and CCG

are equipped in two racks in maximum configuration

System Panel Display (SYPD) to display system internal alarms and the CP load. It

thus provides a continuous overview of the state of the system. The SYP also

displays external alarms such as fire and air-conditioning system failure for

example. It is installed in the Equipment Room or in the Exploitation Room.

Operation and Maintenance Terminals for Input/Output. Two OMTs are provided

for O&M functions.

External memory (EM), for

Programs and data that do not always have to be resident in the CP

An image of all resident programs and data for automatic recovery

Call charge and traffic measurement data.

To ensure that these programs and data are safeguarded under all circumstances, the EM is

duplicated. It consists of two magnetic disk devices (MDD), each of 780 MB capacity. The

EM also has a magnetic tape device (MTD), for input and output. These units are mounted

in a separate device rack (DEVD).

9

3.1.3. Common Channel Signaling Network Control

The common MTP functions in an EWSD exchange are handled by the common channel

signaling network control (CCNC). The UP is incorporated in the software of the relevant

LTG.

A maximum of 254 common signaling channels can be connected to the CCNC via

either digital or analog links. The digital links are extended from the LTGs over both

planes of the duplicated switching network and multiplexers to the CCNC. The CCNC is

connected to the switching network via two 8 Mbps highways (SDCs). Between the CCNC

and each switching network plane, 254 channels for each direction of transmission are

available (254 channel pairs). The channels carry signaling data via both switching network

planes to and from the LTGs at a speed of 64 Kbps. Analog signaling links are linked to the

CCNC via modems.

For reasons of reliability the CCNC has a duplicated processor (CCNP) which is connected

to the CP by means of similarly duplicated bus system. The CCNC consists of (Figure 9):

Upto 32 signaling link terminal (SILT) groups, each with 8 signaling links and

One duplicated common channel signaling network processor (CCNP).

The CCNC, equipped in one rack can handle upto 48 signaling links. Equipments handling

upto 96 signaling links can be equipped in additional racks.

10

4.Subscriber/Administration Facilities in EWSD 1) Rapid call set up:

- Abbreviated Dialing

- Hotline Immediate

- Hotline with Time Out

2) Call Restriction Services:

- O/G Restrictions

- Administration Controlled

- Subs controlled

- I/C Barring

3) Absent Subscriber services

- Immediate diversion

- Diversion on no replay

CCS via digital data links

CCS via analog data links

0 31 0 31

0 7 0 7

SILT group 31

SILT group 0

CCNP 0 CCNP 1

CP bus system

COMMON CHANNEL SIGNALLING NETWORK CONTROLFigure 9

MultiplexerModem

11

- To operator

- To a number

- To announcement

4) Call Completion services

- Diversion on busy

- Call waiting

- Call priority (originating & terminating)

5) Multiparty services

- Conference call

- Tele-meeting

6) Alarm call booking

- Casual

- Regular (number of consecutive days)

7) Services to PBX

- Direct dialing in (for different PBX capacities)

- Line hunting

8) Miscellaneous Services

- Malicious call identification

- All calls

- Special subscribers signal

9) Call charge services:

- Separate counters for Local Call charges, STD/ISD calls charges,

Numbers of calls, Service activation charges and Service usage charges

- Transmission of meter pulses

- Preventive meter observation (adjustable threshold)

12

System Data

Call-handling capacity No. of Subscriber lines max. 250 000

No. of Trunks max. 60 000

Switchable traffic max. 25 200 E.

Supply voltage -48 V nominal direct voltages

Clock accuracy Maximum relative frequency deviation:

Plesiochoronous 10^-9; synchronous 10^11

Signaling systems All conventional signaling systems,

E.g. CCITT R2, No.7

Analog subscriber line Various loop and shunt resistance possible.

and trunks accesses Push-button dialing, Multi-freq. signaling to

Rotary dialing: 5 to 22 pulsse/s

ISDN accesses Basic access 160 kbps (2B+D+sync) B=64kbps,D=16 KBPS

Primary rate access 2048kbps(30B+D+sync)

Digital trunk accesses 2048 Kbps

Traffic routing Predestination max. 7 high-usage routes and

One final route sequential or random selection of

idle trunk of a trunk group

No.of trunk groups exchange:

Max. 1000 incoming and

Max. 1000 outgoing and

Max. 1000 both ways

13

2. DATA LINE UNIT

2.1 Introduction

Subscriber lines and PBX lines in EWSD are connected to digital line units(DLU).The

DLU s can be operated locally in an exchange or remotely.The DLU s are connected to the

switching network via LTG(B-function). A DLU is connected to an LTG by 2 Mbps

Primary Digital Carriers (PDC). However, the local DLU s (DLU s in the main exchange)

are connected to the LTG (B) by 4 Mbps carriers.

For security reasons, a DLU is connected to two LTG s. A subset of CCS#7 according to

CCITT is used for signaling between a DLU and the Group Processor (GP) in the 2 LTG

s.Remote DLU s are installed in the vicinity of group of subscribers. The resultant short

subscriber lines and the flexible concentration of subscriber traffic to the exchange onto

digital transmission links makes for an economical subscriber line network with optimum

transmission .

The following are the important DLU features:

Connection capacity of a single DLU : upto 952 subscriber lines

(depending on type of subscriber line(analog /ISDN),functional units provided and

required traffic values)

Traffic handling capacity : upto 100 erlangs

Connectivity : Analog subscriber lines with

- rotary /DTMF dialing

- call charge indication with 16/12 khz as well as access lines

for

- coin boxes telephones

- analog PBX s with/ without DID

- small and medium-sized digital PBX s

14

subscriber lines for

- ISDN basic access

Growth capability in small modular steps:

4,6 or 8 subscriber line circuits (SLCs) according to module type.

Connection to line/trunk group G(LTGG(B))via one , two or four PCM30

multiplex lines (primary digital carriers ,PDC). The local connection to LTGG can

be realized via two LTGs is 120 .

Common Channel Signaling (CCS) between the DLU and the LTGs. TS16 on

PDC0 and PDC2 used for this purpose .

high operating reliability

- due to the connection of the DLU to two LTGs

- duplication and load sharing of DLU modules handling

central functions (DLU system 0 and 1)

- continuous self-tests

Full availability between the connected subscriber lines and the channels to the

exchange .

All EWSD features ,regardless of whether the DLU is operated locally or remotely .

Identical equipment in all DLUs ,both for local and remote operation.

Integrated test unit for automatic and manual testing of subscriber line

circuits ,subscriber lines and analog telephone sets.

15

Metallic Test Access(MTA) giving external subscriber line testing systems access

to the access to the analog subscriber lines connected to the

DLU

DLU emergency operation ( in the event of total failure of the transmission routes

to the main exchange)

Remote control unit (RCU) used for remote operation and consisting of upto six

remote DLUs. Each R-DLU of the remote cluster has an SASC module (stand alone

service controller) for emergency operation.

2.2 Structure

In the majority of cases, the modules belonging to a DLU are arranged in module frames

with two rows of modules .module frames with one row of modules are only used in 2130-

mm racks. In the DLU a row of modules in a module frame is termed as a shelf. A shelf is

subdivided into a left-hand right –hand half shelf (as seen from the module side of the

module frame).

To understand the architecture of the DLU , the DLU structure will be discussed in the

following sequence:

DLU system comprising of central card

Ringing &metering Voltage Generation ,

Bus system comprising of

-Control network for processors

-4096-kbits/network for speech signals

peripherals cards which include Line cards and Test cards.

DCCs, i.e.,direct current converters.

16

17

DLU system

A DLU system contains the following functional units:

(a) a control for digital line unit(DLUC),

(b) a digital interface unit for DLU(DIUD)

(c) a clock generator (CG) &

(d) two bus modules (BD)

A DLU system is a failure unit which is duplicated in the DLU . Both DLU systems are

housed together in a module

the DLU system 0 (DLUC0,DIUD0,..CG0 and BD..0) are contained in the upper

half (shelf 0) of the module frame .

the DLU system 1 (DLUC1,DIUD1,..CG1 and BD..1) are contained in the lower

shelf(shelf 1).

The functional units DLUC, DIUD and CG are also referred to as central units. If a fault

occurs in a central functional unit of one the DLU systems ,normal call handling is still

possible via the other DLU system.

DLU controller(DLUC)

For security reasons and to increase throughput ,there are two DLUs in the DLU. They

work independently in a task sharing mode. If one DLUC fails the second DLUC can

handle the tasks alone.

The DLUC controls the sequence of DLU –internal functions and either distributes or

concentrates the signaling between the subscriber line circuits and DLUC. The DLU

internal control network connects the DLUC with the shelves. All functional units equipped

with their own microprocessors are addressed through this control network.

The units are polled cyclically by DLUC for messages ready to be sent , and are accessed

directly for the transfer of commands and data from DLUC.

18

The DLUC carries out test and supervision routines to detect errors .

LEDs on the DLUC indicate the operating mode & the status of the PDCs.

Digital Interface Unit for DLU(DIUD)

The DIUD has two interfaces for the connection of two PCM30 multiplex lines (PDCs)

connecting the DLU with the LTG. Either balanced or coaxial can be connected. A total of

128 channel pairs are available between the SLCAs and the DIUDs:

- 120 channels for the transmission of user information

- 8 channels for transmission of tones for routine loop tests as

well as audible tones during emergency service.

The following are the important of DIUD:

Takes the control information arriving from the LTG from channel 16 , of a

PDC(DIUD0 takes the control information from PDC0,DIUD1 from PDC2).

The DIUD forwards the incoming control information from this LTG to the partner

DLUC ( i.e. the DLUC belonging to the same DLU system as that of the DIUD).In

the opposite direction the information coming from the DLUC is inserted in channel

16 of the same PDC and transmitted to the LTG.

Provides the interfaces to a DLU –internal 4096-kbit/s network to the individual

shelves. The user distributed to and from the SLM modules via this 4096 – kbits/s

network.

Derives a signal for synchronization of the clock generator from the line clock of

the PDC.

Performs test and supervisory routines and detects any occurring errors.

19

The channel contents of the PDC with CCS are forwarded with the even numbered

channels of the 4096 –kbit/s network ,the channel contents of the PDC without CCS

to the odd channels.

A test loop is switched via the DIUD for the cross office check(COC)

Conducted by the LTG.

LED s in the module faceplate indicate the operating mode of the DIUD and the

PDC s.

Digital Interface Unit for Local DLU interface ,Module D(DIU:LDID)

Usually the local DLU is connected to the LTG via a single 4Mbps interface having 64

time slots instead of 2 independent PDCs.

For connecting a local DLU to LTG(B) ,the interface in the DLU is DIU :LDID in place of

DIUD . the DIU:LDID in place of DIUD.The DIU:LDID has 4096 Mbps interface. For

such a connection a balanced copper line is used .the DIU:LDID handles the transmission

of the contents of 60 user channels and a control information channel via a single 4096 –

Mbps multiplex line ( instead of via 2 PDCs.) The main tasks of the DIU:LDID are similar

to those of the DIUD.

20

3.LINE TRUNK GROUP

3.1 Introduction

The line/trunk group(LTG) is a subsystem of EWSD. The LTG forms the interface between

the digital environment of an EWSD exchange and the switching network(SN).

LTG types:

Different hardware versions of LTGs exist for various configurations above. This

documents deal only with line/trunk groups of type G, i.e. LTGG:

LTGG(B-function) for DLU and PA

It is possible to connect combinations of DLU and PA to the same LTGG. THe transfer rate

is 2048 kbit/s.

It is also possible to connect trunks( without or without multi frequency code MFC),

provided they have the same transfer rates as DLU/PA. DLUs can be operated as local or

remote. Local operation can be converted to remote operation.

LTGG(C-Function)

Exclusively for trunks with/without MFC. The transfer rates are 2048 kbit/s.

The transfer rate on the secondary digital carrier(SDC) from LTG to the SN and vice versa

is 8192 kbit/s(8 Mbps). Each of these SDC s has 128 time slots of 64 kbit/s each, out of

which 127 time-slots are used for user information and one time slot of messages. User

information is the information relevant to the communication partners(voice, text, data,

images). Messages are used for interprocessor communication in the EWSD system, e.g., in

the case of the LTG, for communication with (a) the coordination processor, (b) other

LTGs and ( c) the CCNC. User information and messages are transferred together.

21

22

LTG Functions: The main functions of the LTG are :

(a) Call processing functions include:

Receiving and evaluating signals from the trunk and subscriber line

Sending signals

Sending audible tones

Sending messages to the CP and receiving commands from the CP

Sending/receiving reports to/from the group processors(GP)

Sending/receiving orders to/from CCNC

Controlling the signals to DLU, PA

Adapting the line conditions to the 8Mbps standard interface to the SN

Through-connection of messages and user information

(b) Safe guarding functions include:

Detecting errors in the LTG(without external text equipment)

Detecting errors on the connections path with in the exchange via cross-office checks

and bit error ratio counting(BERC)

Transferring error messages to the CP

Evaluating errors to determine penetration range

Initiating measures corresponding to the penetration of an error(e.g., blocking of

individual channels or blocking of entire functional units of the LTG).

Exchanging routine text messages to the CP, so that the CP can detect a faulty LTG if

the LTG itself is not able to send error messages.

( c) Administrative functions include:

Sending messages to the CP for traffic measurements and traffic observation

Switching of text connections

Testing of trunks and port-specific areas of the LTG using the automatic test equipment

23

for trunks(ATE:T) integrated in EWSD and the automatic test equipment for

transmission measuring (ATE:TM).

Indicating important information(e.g., channel assignments) to the functional units

Creating, blocking, releasing devices via MML commands

3.2 Connections

As indicated under sec 1.2 two types of connections exist for LTG time-slots:

(a) Subscriber connections

(b) Message connections

Subscriber connections A subscriber connection is a connection that carries user information. Subscriber may

include ordinary telephone subscribers as well as telecopiers and facsimile equipment. To

set up subscriber connection each LTG has 127 time slots (1-127), also called channels, for

8-Mbit/s multiplex system. 120 time slots are used for transmission. Subscriber connections

through-connected by the SN. Each subscriber connection occupies one time slot in the

forward direction and one time slot in backward direction; the two time slots are identical

within their multiplex system. The calling subscriber A is assigned time slot x, for example,

by the group processor, GP. This GP is allocated in LTG of A-side(in fig 2.1:LTG1). The

called subscriber B is as signed time slot y, for example, by the CP. The SN combines time

slots x and y in a time slot z.

The two switching networks(SNO and SNI) work in hot standby mode. An LTG always

sends and receives the user information on the SDC through both SN-halves(SNO and

SNI). Thus both SN-halves contain the same user information. However, an LTG assigns

only the user information from the active SN-halves to the respective subscriber(A- or B-

side). The other SN-half is designated as standby and, in the event of a failure, is able to

take over immediately and send and receive the up-to-date user information. To do this, it

must be configured from standby to active. The link interface unit(LIU) between the LTG

and SN, located the LTG then receives the information from the other SN-half.

24

Connections of messages-channels

The GP of LTG exchanges messages(inter processor communication) with

(a) the GP of other LTG in the same exchange,

(b) with the CCNC, and

(c) with the CP.

To do this, each LTGs uses time slot 0 of each SDC to and from the SN. This connection is

called message channel (MCH). The message channel is implemented as semi permanent

which is set up when the system is placed in service or restarted and then remains

connected. Like subscriber connections, message channels are always through-connected to

the 2 Message Buffers simultaneously through the respective SN-halt. The GP are the

message buffer for the CP, however, uses only the messages from the active MCH; the

other MCH is designated as standby. Since the MB-0 and MB-1 work on load-sharing

basis(i.e. GPs of half LTGs communicate with the CP via MB-0; the other half LTGs being

handled by MB-1), the standard distribution of the ACTIVE message channel of LTGs to

the MBs is as below:

1. Messages from the GP:

The messages originating in the GP are transmitted in time slot 0 on the MCH through the

SN and to the MB. All LTGs are connected to the SN in parallel.By design each LTG is

assigned to the specific SN-half foe the message distribution .The GP of LTG1 sends a

message to the LIU to SN1. In the process the LIU inserts the message in time slot 0 to the

SN. SN1 forwards the message in time slot x. On the MCH from SN to the MB, SN1

transfer the messages of all LTGs serially to the MB. The SN transfer the message from

LTG1 I time slot2.

An analogous procedure is used for a message that is to the simultaneously transfer from

LTG63 to the CP. The difference is that LTG63 is assigned to SNO, at different time

slot(y) is used within SNO, and a different time slot(126) is also used to transfer he

message to the MB. Consequently MBO receives the message from LTG63, MB1 receives

the message from LTG1. The MB buffers this data until it is received by the input/output

processors (IOP) in CP. The corresponding IOP determines whether the data involves a

25

message for the CP or a report for a GP and, accordingly, stores the messages in the input

list and the repots in the output list of the CP.

If one of the units on the message transmission path becomes faulty(e.g. SN-half or MB),

fault detection mechanism configure the defective unit from active to unavailable. The unit

that was previous standby then takes over the functions of the faulty unit. Assuming that

SN1 was configured to unavailable, SN0 takes over all those LTGs which are normally

assigned to SN1(LTG1, LTG3, LTG4, LTG6). The GP of LTG1 then sends the message to

SNO. To do this. It uses the MCH represented by the broken line in LTG1 as the active

MCH. SNO forwards the message in time slot x (the time slot is the same in both SN-

halves). On the message channel from SNO to the MB, this message is assigned to time

slot2. The IOP in the CP no longer polls MB1 as usual, but rather MBO, from which it

obtains the messages fro LTG1 (as well as from the other LTGs which previously

transmitted via SN1).

2. Message to GP:

Data being sent to a GP (e.g. commands from the CP or report from other GPs) are read by

the IOP from the CP memory in it. The IOP forwards the data to the MB associated with

the respective LTG (e.g. MB1 for LTG1). The MB buffers the data and assigns the data to

the assigned time slots to SN. For LTG-1, this is time slot2. SN1 transfers the message in

time slot x and forwards it to LTG-1 in time slot 0 (the time slot in the SN of the same for

the forward and backward directions, as are the time slots on the MCH). The other LTG

receive their messages in the same manner. The LIU extracts the messages from the

information received from the SN(user information and messages) and forwards the

messages to the GP. The above description applies analogously for LTG63 (and other

LTGs), as well as for reconfigurations in the event of faults.

26

Functional Units

The line/trunk group LTGG is made up of the following functional units:

Functional unit in the line/trunk unit(LTU)

Functional unit in the signaling unit (SU)

Group switch and interface unit(GSL)

Group processor(GP)

line/truck unit

The line/trunk unit (LTU) is a logical unit which can have a number of different functional

units(fig 3.2). The purpose of these functional units is to adapt connected lines to the

internal interfaces of the LTG and to equalize signal delays(synchronization of exchange

bit rate and line bit rate). They also process the signals to and from the connected lines.

By means of the signal highway output (SHHO), the LTU receives commands from the

GP (e.g. exchange codes to be transmitted); by means of the signal highway input (SIHI),

the LTU sends peripheral-event information to the GP. Address signals (from the GP to the

LTU and SU) control the SPH and SIH used to link the LTU with the GSL an GP.

The functional units can be listed below an be plugged into the LTU.

(a) Digital Interface Unit (DIU)

(b) Local DLU interface, module B (DIU:LDIB

Conference unit, module B(COUB)

The conferencing unit occupies this lot reserved for LTUs and hence, is configured as an

LTU. A single COUB module contains four individual conference units. Each of the

conference units can connect up to 8 channels (e.g. 8 subscribers). It is also possible to

cascade to conference units, so that as many as 14 channels can be connected.

Code receiver (CR)

The following type of Code receiver can be used in the LTU if the capacity for CR in the

SU has been exceeded:

27

- multifrequency code receiver (CRM)

- Code receiver for push-button (DTMF) dialing (CRP)

Code receivers are implemented as a digital signal processing module, extended (SPME).

The SPME is programmed for the functions of CRP or CRM (and module RM:CTC in the

SU) via the firmware. An SPME can accommodate 8 CRs.

Automatic test equipment (ATE)

The ATE is used in one of two variants

The automatic test equipments for trunks (ATE:T) is used for routine testing of trunks and

tone generators (TOG). The ATE:T consists of the test equipment module for level

transmitting and measuring (TEM:LE).

The responder used with ATE:T can be, for example, the EWSD system-integrated end-to-

end test equipment, answer equipment (module) (ETEAE), another responder (e.g.

implemented with TEM:LE), or an automatic subscriber.

The automatic test equipment for transmission measuring (ATE:TM) is the equipment used

for manual testing of trunks with the trunk work stations (TWS) and serves as director or

responder within the ATME2 when testing international trunks. The ATME2 is specified

by CCITT. The ATE:TM consists of module ATE:TM. The modules of ATE, like the

ETEAE, are plugged into the LTU of LTG.

The operationally controlled equipment for announcement (OCANEQ)

For an individual digital announcement system (INDAS), it can be plugged into slots of the

LTU.

Signaling Unit

The signaling unit (SU) is logical unit that can accommodate various functional unit . In the

LTGG, the functional units may be: TOG, CR, RM:CTC.

28

(a) Tone generator (TOG)

The TOG centrally generates the audible tones required for all LTUs as well as the

frequencies for testing the code receiver. These frequencies are stored as bit patterns in a

replicable memory chip. Bit patterns are converted into analog form in the functional unit

requiring them.

(b) Code receiver (CR)

Depending on the type of LTG, the SU contains code receiver for push bottom dialing

(CRP) and/or for multifrequency code receivers (CRM) for trunk with channel associated

signaling (CAS). The CRP or CRM is assigned to DTMF subscriber line or MFC trunks

only for the digit input.

(C) Receiver module for continuity check (RM:CTC)

When trunks with common channel signaling (CCS#7) are used, the receiver module for

continuity check (RM:CTC) is required.After a connection is set up, an RM:CTC can be

assigned to the incoming line. A signal transmitted by the TOG on the outgoing line and

looped back at the destination is detected and analyzed. It is recognized whether the call

setup has been successful and whether line attenuation is too high for satisfactory

transmission quality. If the attenuation is too high, the connection is released, and a new

connection is set up.

The SU is connected to the GSL via SPHO/I and to the GP via SIHO/I. The SU receives

commands from the GP via SIHO and sends signaling characters to the GP via SIHI.

SPHO/I and SIHO/I are controlled by address signals (from the GP to SU).

In the case of MCH signaling, the in band signals from the DIU are forwarded to the GSL

via SPHI. From there, the signals are fed to the CRM via SPHO. The CRM evaluates the

signals and signals and sends the results of evaluation to the GP.

29

Group processor

The functional unit group processor (GP) is an independent control unit. The GP controls

the functional unit of the LTG and comprises the following individual module

1. Clock generator and signal multiplexer (CGSM)

2. Processor memory unit (PMU)

3. Signaling link control (SILCB), when DLU/PA are connected to LTG

1. CGSM module (Clock generator and signal multiplexer)

The clock generator and signal multiplexer (CGSM) in the GP is made of three parts:

- the clock generator part (CG part)

- the message channel part (MCH part), and

- the signal multiplexer part (SM part).

The CG part which is the clock pulses supplied from both SN-halves via the GSL (LIU)

part. Using the supplied frame mark bit (FMB), the CG part synchronizes the LTG clock

with the SN clock. To do this, it derives the synchronization pulses SYNI from the FMB on

an SN-specific basis (SYNI-0 for SN0, SYNI-1 for SN1). The CG part selects one of the

two synchronization pulses SYNI and synchronizes the LTG clock to this pulses.

The synchronization pulses SYNI are monitored by the CG part. An alarm is generated if

more than one period of this synchronization is lost. Synchronization of the LTG clock

with SYNI is also monitored. The CG part sends alarm data to signal buffer of the PMU.

Alarm data includes:

- Alarm in the event of synchronization failure

- Alarms for LTG clocks with reference to transfer rates of 2048 kbit/s

- Indication of which synchronization pulse is currently being used

30

3.3 Group Processor Software

The GP software controls the functional units of the LTG. It monitors the timing of

sequences in the LTG and processes events from the LTG and from the LTG periphery. To

property perform their call processing, administrative and safeguarding tasks, the LTG s

are in constant communication with the CP (interprocesser communication). The following

types of messages are exchanged.

The CP, being higher in the processor hierarchy, sends commands to the GP.

Conversely, the GP sends messages to the CP.

A GP exchanges reports with other Gps,

With the common channel signaling network (CCNC), the GP uses orders.

4. SWITCHING NETWORK 4.1 Introduction

Switching network (SN) performs the switching function for speech as well as for

messages in an EWSD exchange. For this purpose it is connected to LTGs and CCNC

for speech/data and to CP (through MB) for exchange of control information. Switching

network with ultimate capacity up to 63 LTGs is called SN DE4 . for larger exchanges

SN DE5.1 is used which can connect up to 126 LTGs. Similarily SNDE5.2 can connect up

to 252 and SN DE5.4 upto 504 LTGs.

31

Figure 1.Position of Switching Network in EWSD

4.2 General Features

Switching network is provided in capacity stages SN:63LTG to SN:504LTG i.e. up to 63

LTGs can be connected . The modularly expandable SN has negligibly small internal

blocking and can be used in EWSD exchange of all types and sizes.

The self monitoring switching network uses a uniform through connection format. Octets(8

bit speech samples) from the incoming time slots are switched to the outgoing time slots

leading to the desired destination fully transparently. This means that each bit of all octets

is transmitted to the output of the Switching network in the way that it appears at the input

(bit integrity).For each connection made via the switching network, the octets have the

32

same sequence at the output as at the input(digit sequence integrity).For each incoming

octet to be switched at any time to any outgoing highway at any time to any outgoing

highway at the output of the switching network. The time slots used in switching network

for making through connections make up a 64 k bit/s connection path.

All of the switching network’s internal highways have a bit rate of 8192 bits/s

(Secondary Digital Carriers, SDCs). 128 time slots with a transmission capacity of

64Kbits/s each (128x64=8192Kbits/s) are available on each 8192Kbits/s highway. Separate

cables each containing several (eight or sixteen) such internal highways, are used for each

transmission direction. All externally connected highways also have the same uniform bit

rate.

The switching network combines the numerous switching network functions in a few

module types. These modules work at very high through-connection bit rates; 8192Kbits/s

and some even at 32768 Kbits/s. for example 1024 connections can be switched

simultaneously through a space stage with 16 inputs and 16 outputs. Although these highly

integrated switching network modules switch a large number of connections with a high

degree of reliability, the EWSD switching networks are always duplicated. The amount of

space needed for the switching network in the EWSD exchange is still very low despite this

duplication

Two different switching network versions have been supplied in India

Switching network [SN] supplied with first 110K order.

Switching network B [SN(B)] supplied with subsequent orders.

4.3 Position And Functional Structure:

Switching network is connected to LTGs and CCNC for speech/data and to CP (through

MB) for exchange of control information. Figure 1 shows the position of switching

network in EWSD exchange with reference to other equipments.

33

For security reasons, entire SN is duplicated. The two sides of SN (Sn0 and SN1) are called

planes. The external highways for both transmission directions i.e. between the Switching

network and one LTG or between the switching network and one Message buffer

unit(MBU) are identified .

SDC:LTG interface between SN and LTG : time slot 0 for message exchange

between the LTG and coordination processor(CP) as well as between two LTGs, time slot 1

to 127 for subscriber connections.

SDC:CCNC interface between SN and the common channel signaling

network(CCNC):for common channel signaling.

SDC:TSG interface between SN and a message buffer unit assigned to CP

(MBU:LTG) for message exchange between the CP and the LTGs as well as between the

LTGs

SDC:SGC between the SN and an MBU:SGC of the CP for setting up and clearing

connections.

Switching network in EWSD exchange uses time and space switching and therefore it is

functionally divided into Time Stage Group(TSG) and Space Stage Group(SSG). SN DE4

with capacity stage SN:63LTG has a TST structure and TSG/SSG division is not applicable

in this case.

TSGs and SSGs are interconnected through internal 8 Mb/s interfaces called SDC:SSG.

TSGs of both planes are connected to SSGs of both planes , and thus these provide further

security.Each TSG and SSG have its own Switch Group Control (SGC) that is connected to

CP via MB through interfaces SDC:SGC.

TABLE 1: SN Capacity stages

Capacity stages of

switching network

SN:63LT

G (DE

SN:126LT

G (DE 5.1

SN:252LTG SN:504LTG

34

4) ) (DE 5.2) (DE 5.4)

Switchable

traffic(E)

3150 6300 12600 25200

Local exchanges

No. of lines

30000 60000 125000 250000

Transit exchanges

No. of trunks

7500 15000 30000 60000

Structure TST TSSST TSSST TSSST

Connectable no. of

LTGs or

LTG+CCNC

63

or 62+1

126 or

125+1

252

or 251+1

504

or 503+1

4.4 Capacity Stages

The present version of SN is available in capacity stages SN:63LTG, SN:126LTG,

SN:252LTG, and SN:504LTG. Modular structure permits partially equipped SN. Up

gradation from DE5.1 to DE5.2and from DE5.2 to DE5.4 is possible with the help of

supplier. SN DE4 is not up gradable to DE5.1 as DE5.1 as TSG and SSG are not separately

identified in SN DE4. The traffic handling capacity, connect ability for various capacity

stages of SN are shown in Table 1.

4.5 Functional Units Of Sn

Switching path

The Switching network is subdivided into time stage groups (TSG) and space stage groups

(SSG). Due to its modular structure, the EWSD switching network can be partially

equipped as needed and expanded step by step. The switching network uses the following

switching stages:

35

One time stage incoming(TSI)

Three space stages (SS)and

One time stage outgoing (TSO).

These time and space stages (functional units), shown in figure 3, are located in the

following module types;

Link interface module between TSM and LTG (LIL)

Time stage module (TSM)

Link interface module between TSG and SSG (LIS)

Space stage module 8|15 (SSM8|15)

Space stage module 16|16 (SSM16|16)

The switching network capacity stage SN:63LTG, however has a TST structure with only

one space stage in figure4. Module type LIS and SSM 8|15 are not there in SN: 63 LTG.

Further, the modules and the TSGs/SSGs are interconnected.

LIL & LIS :

The receiver components of the LIL and LIS compensate for differences in propagation

times via connected highways. Thus, they produce phase synchronization between the

incoming information on the highways. These differences in propagation times occur

because an exchange’s racks are set up at varying distances to each other. Module LIL is

connected on the interface to LTGs and has 4 inputs and 4 outputs while module LIS is

connected on the interface to SSG and has 8 inputs and 8 outputs.

36

TSM:

The number of TSMs in switching network is always equal to the number of LILs. Each

TSM contains one time stage income (TSI) and one time stage outgoing (TSO). The TSI

and the TSO handle the incoming or outgoing information in the switching network.

Between input and output, octets can change their time slot and highway via time stages.

Octets on four incoming highways are cyclically written into the speech memory of a TSO

(4x128=512 locations corresponding to 512 different time slots). The speech memory areas

0and 1 are used alternately in consecutive 125- microseconds periods for writing the

octets.The connections to be made determine the octet sequence during read-out to any one

of 512 time slots and then transferred via four outgoing highways.

SSM 8|15 and SSM 16|16:

The SSM 8|15 contains two space stages as shown in figure 6. one space stage is used for

transmission direction LIS SSM 8|15 SSM 16|16 and has 8 inlets and 15 outlets

while a second space stage is used for transmission direction SSM 16|16 SSM 8|15

LIS and has 15 inlets and 8 outlets. Via space stages, octets can change their highway

between input and output, but they retain the same time slot. Space stages 8|15, 16|16 and

15|8 switch the received octets synchronously with the time slots and the 125-microsecond

periods. The connections to be switched change in consecutive time slots. In this process,

the octets arriving on incoming highways are “spatially” distributed to outgoing highways.

In capacity stages with a TST structure, the SSM 16|16 switches the octets received from

the TSIs directly to the TSOs.

TABLE 2: List of Modules used in SN

PCB No. of cards in

SN:63 LTG

No. of cards

in TSG of

SN:DE5

No. of cards

in SSG of

SN:DE5

Remarks

LIL 16 16 - One LIL can connect up to 4 LTGs.

The cards LIL and TSM are always

used in pairsTSM 16 16 -

LIS - 8 16 This PCB has 8 inlets and 8 outlets.

37

LIS and SSM 8|15 are always used

in pairs

SSM8|15 - - 16

SSM16|16 4 - 15 Used to cross connect outlets of 16

SSM8\15 to inlets of SSM 15|8

LIM 1 1 1 These two PCBs are used in the

SGCSGC 1 1 1

DCC(B) 2 2 2 Separate shelf is provided for the

DCC(B)s in the rack

Control section:

Each TSG, each SSG, and with SN:63LTG, each switching network side has its own

control. These controls each consist of two modules viz. switch group control(SGC) and

link interface module between SGC and MBU:SGC(LIM)

An SGC consists of a microprocessor with accompanying memory and peripheral

components. The main tasks of an SGC are to handle CP commands (such as connection

setup and clear down), message generation and routine test execution. Apart from the

interface to the message buffer unit(MBU:SGC), an LIM has a hardware controller (HWC)

and a clock generator for clock distribution.

Firmware:

The firmware for the switching network is permanently stored in the program memory of

each SGC. For this reason , it does not have to be loaded or initialized by the coordination

processor(CP). SN firmware is organized in the following manner:

Executive control programs

Call processing programs

Maintenance programs

Startup and safeguarding programs

38

5.MESSAGE BUFFER

5.1 Introduction

The message buffer B (MB (B)) is assigned to the CP area of the EWSD.

Functional units of the message buffer (MB) have the job of controlling message exchanges

between the following subsystems:

Between the CP and the LTGs:

Call processing messages to set up circuit connections, administrative and

safeguarding or maintenance message

Between the LTGs themselves:

Call processing messages

Between LTG and the CCNC:

Call processing messages between exchanges via common channel signaling

links

Between CP and switch group control (SGC):

Setting instructions for switching network.

Depending on the source and destination of the control information, the following terms are

used to describe the exchange of data:

- Data transfer from the CP to a GP : command

- Data transfer from a GP to the CP : message

- Data transfer from a GP to another GP : report

- Data transfer between CCNC and GP : order

Message routes in EWSD

The message routes in EWSD from a two-layer star network, with the input output

processor for message buffer (IOP:MB) representing the central point.The processors of the

SYP, CCNC, MBU, CCG and CP devices are interconnected via the first layer of the star

network. The IOP:MB has output lists in the common memory (CMY) of the CP. Here

39

there are output lists for SYP, CCNC, MBU and CCG. There is an input list for input from

the call-processing periphery and an overflow list for messages.

The second layer of the star network is located after the MBU:LTG in the layer, message

are distributed between or collected in the MBU and LTG with the aid of SN. The

MBU:SGCs implement the exchange of message with up to three SGCs.

Communication between the GPs or DLUC and the CCNC (without the participation of the

CP processing unit (PU) is made possible by a transfer list for the CCNC and for each

MBU in the common memory (CMY) of the CP.The IOP:MB has direct access to the

CMY of the CP.

Fig.1 : Two Layered Star Network For Message Routes in EWSD.

40

Functions For Handling Message Traffic

All processors participating in the transport of messages perform the following functions

for handling messages.

- Transport

- Distribution and collection

- Buffering

- Saving

Distribution and collection require a speed adjustment to be made between message inflow

and outflow. This adjustment is made with the aid of buffers in the MBU and IOP:MB.

Messages to be processed may have to wait for processing, since the processing since the

processing processes can be “in progress”. For this reason, buffers for the processes are

also needed to adjust the transport speed to the processing speed. Message

queues can form in the buffers. This ensures flexible speed adjustments between message

transport, distribution and processing.The MB(B) has been designed to meet the higher

performance demands of the CP113.The MB(B) in itself is fully redundant and is made up

of an MB(B)0 and an MB(B)1. These operate on a load-sharing basis. Fig. 2 shows the tie-

in of message buffer to its environment.

The MB(B) is connected to the other units as follows

With the LTGs each via one 64-Kbits/s channel on the secondary digital carriers

(SDC:TSG, SDC:LTG).

The relevant multiplex highway channels are linked to each other in the switching network

via semi permanent connections. Normally the connected LTGs are distributed equally

over both system halves (MB-1/SN/side 1).

With the SGCs via multiplex highways (SDC:SGC)

41

With the input/output processors (IOP:MB) of the CP via the bus systems

B:MBG0 and B:MBG1.

In the input direction, the MB(B) can receive

- Messages from the LTGs and the SGCs (for the CP)

- Reports from LTGs (for other LTGs)

- Orders from the LTGs (for the CCNC)

It processes these for transmission to the IOP:MB of the CP, stores them and passes them

to the IOP:MB on request.

In the output direction, the Mb9B) can receive

- Commands from the CP (for the LTGs and SGCs)

- Reports from the LTGs (for other LTGs)

- Orders from the CCNCs (for the LTGs)

It processes these for transmission on multiplex highways to the LTGs and SGCs.

Some special features of the MB(B):

Load sharing and a high level of reliability due to redundancy

Control of broadcasting and collective connections:

A specific software (load type) is carried simultaneously to all LTGs with the same

functional structure via broad cast links during initial start or system recovery. In the case

of collective connections, the same commands are sent simultaneously to certain LTGs,

e.g. tariff switchover.

Control of multi-broadcast connections, i.e. up to 16 load types can be

simultaneously distributed to the LTGs.

High transmission performance (1300MSU/s for each transmission direction, 128

byte/message)

Modern technology ( TTL-ALS and TTL-FAST)

Microprocessor control with permanently stored software (firm ware)

Self-monitoring and Simple growth capacity in stages.

42

5.2 Structure

Depending on the capacity stage, the MB(B) will consist of one to four duplicated message

buffer groups (MBG). MB-0 contains the MBG-00,01,02,03 and MB-1 contains the MBG-

10,11,12,13. Each non-duplicated MBG is installed in one module frame.

Message buffer group (MBG)

An MBG is made up of the following functional units (fig. 3)

2 nos. of MBU:LTG (message buffer unit for LTGs)

MBU:SGC (message buffer unit for switch group control )

CG (group clock generator)

MUX (multiplexer-forming to interface to the SN)

Interface adapter to IOP:MB

a) MBU:LTG (message buffer unit for LTGs)

The MBU:LTG consists of a maximum of four transmitter/receiver controls (T/RC) and a

message distribution module (MDM). The T/RC module can supply up to a maximum of

16 line/trunk groups (LTGs). One MBU:LTG will therefore allow expansion of an

exchange in stages of 16 LTGs. A maximum of four T/RCs of an MBU:LTG can be

interconnected via a message distribution module. This module distributes the messages

arriving from the IOP:MB to a particular T/RC module and collects the messages injected

by the LTG into T/RC modules, in order to transmits them to the IOP.

The MBU:LTG has the following tasks`

Distributing and forwarding outputs (commands, reports, orders) from the CP to the

LTGs.

Collecting inputs (messages, reports, orders) from the LTGs and forwarding these

to the IOP:MB and thus to the input and transfer lists of CP.

Detecting and executing internal MBU commands from the CP, e.g., disconnecting

a specific message channel.

43

Forwarding messages relating to internal MBU processes to the CP, e.g., ‘a specific

message channel has been disconnected’.

Carrying out the special broadcasting function. During broadcasting, the same

information can be transmitted with only two broadcasting commands from the CP to all

the LTGs. A case in point might be, for instance, where software is related into the RAM

memory of the GPs in the LTGs.

Carrying out the special collective command function. By means of a collective

command, the same messages can be transmitted to certain LTG groups, e.g., switching to

a new tariff.

b) MBU:SGC (Message buffer unit for switch group control)

The MBU:SGC is combined into a common module (IOPC) with the interface adapter to

the IOP:MB. In principle, an MBU:SGC has the same structure as an MBU:LTG. But

because it only supports a maximum of three control channel pairs, the message

distribution module (MDM) in this case is dispensed with. The three channel pairs, one for

each transmission direction on three different highways can be associated with up to three

different switch group controls (SGC) in the switching network. Incoming and outgoing

messages via the three channels (control information and acknowledgements) are

exchanged directly with the IOP:MB via output or input FIFOs.

The MBU:SGC performs the following tasks:

Buffering commands from the CP and distributing and forwarding these to a

maximum of three switch group controls.

Buffering messages from the switch group controls and forwarding these to the CP

Identifying and executing internal MBU commands from the CP.

Forwarding messages relating to internal MBU operations to the CP.

c) Group clock generator (CG)

Every MBG contains a group clock generator (CG). It is accommodated in one module

(CG/MUX) together with the multiplexer and performs the following tasks:

Generating the exchange clock pulse of 8192 KHZ and the 2-KHZ frame mark bit

(FMB) used for synchronization.

44

Receiving the master clock (8-KHZ) from one of the two central clock generations

(CCG(A)). The master clocks synchronize the clocks generated in the CG. The first

MBU:LTG of an MBG monitors the CG and signals alarms to the CP.

The exchange clock and the frame mark bit are forwarded to MBU:LTG or the MBU:SGC,

which in turn transmits these together with the transmit data to the switching network for

onward routing to the LTGs or the switch group control (SGC). The GCG in the SGC

synchronizes the clocks it has generated with the aid of the incoming clocks and transmits

these to the switching network. From here they are retransmitted to the MBU:LTG with the

data received by the LTG.

The following clocks are carried via strip lines to individual modules of the message

buffer:

8MHZ : 8192-KHZ-1:1 clock

4MHZ : 4096-KHZ-1:1 clock

SYN8 : 2-KHZ synchronizing pulse (pulse width 122ns)

SYN4 : 2-KHZ synchronizing pulse (pulse width 244ns)

d) Multiplexer

The multiplexer (MUX) is linked via two secondary digital carriers to the switching

network. Messages are exchanged with corresponding LTGs via 63 incoming and 63

outgoing channels on these carriers. As can be seen in fig.2, the multiplexer concentrates

the data stream of two MBU:LTGs. Every one of the maximum four T/RCs of an

MBU:LTG feeds two times eight channels via a 4-Mbit/s highway into the multiplexer.

The 63 incoming channels from the switching network of the two digital carriers are

distributed by the multiplexer to the four T/RCs of the corresponding MBU:LTG.

45

e)Interface adapter

Every MBG is connected with a separate data bus (B:MBG) to the IOP:MB0 and the

IOP:MB1. The two IOP cables are junctioned in the MBG and linked to the respective

transmitters and receivers. Transmitter outputs and receiver inputs are connected to internal

MBG bus. The interface adapter has the task of converting the IOP:MB push-pull signals to

TTL form and vice-versa.

Capacity Stages :

The present version of SN is available in capacity stages SN:63LTG, SN:126LTG, SN:252LTG, and SN:504LTG. Modular structure permits partially equipped SN. Up gradation from DE5.1 to DE5.2and from DE5.2 to DE5.4 is possible with the help of supplier. SN DE4 is not up gradable to DE5.1 as DE5.1 as TSG and SSG are not separately identified in SN

6.COORDINATION PROCESSOR

6.1 Introduction

The EWSD system consists of number of largely autonomous subsystems. The subsystems

each have their own microprocessor controls, for example the controls for the digital line

units (DLUC) and the groups processors (GP) in the LTGs.The distributed microprocessor

controls and the data transfer between them are coordinated by the coordination processor

(CP). Fig. 1.1 shows the position of the CP in the EWSD switching system.

46

Fig.1.1 : Position of the CP113 in EWSD 1 The CP performs the following coordination functions:

Call Processing

Digit translation

Routing administration

Zoning

Path selection in the switching network

Call charge registration

Traffic data administration

Network management

47

Operation & maintenance

Inputs/outputs to and from external memories (EM)

Communication with the operation &maintenance terminal (OMT)

Communication with data communication processor (DCP)

Safeguarding

Self-supervision

Error detection

Fault analysis

The coordination processor 113(CP113) is supplied for all sizes of switching

center. The CP113 is a multiprocessor which can be expanded progressively (by adding

call processors). It satisfies all safeguarding and performance requirements exceptionally

well.The CP area also includes the system panel (SYP). The SYP indicates alarms (audio &

visual) and advisories from system-internal and system-external supervisory units.

Other important functions in the CP area are handled by:

Message buffer (MB).

Central clock generator (CCG).

6.2 Structure

The CP113 consists of a modular multiprocessor system with a processing width of 32 bits

and an addressing capacity of 4 Gbytes. It is formed by the following functional units

Base processors (BAP)

Call processors (CAP, not included in the basic capacity stage).

Input/output controls (IOC),

Bus to the common memory (BCMY),

Common memory (CMY) and

Input/output processors (IOP) (for the call processing and operation & maintenance

periphery).

Functional unit Minimum Maximum

48

BAP 2 2

CAP 0 6

IOC 2 4

CMY

(Base=4-MbitDRAM)

64MB 1024MB

IOP:MB(LTG/SGC) 2 8

IOP:MB(CCG) 2 2

IOP:MB(SYP) 2 2

IOP:MB(CCNC) 2 2

IOP:TA 2 2

IOP:MDD 2 2

IOP:MTD 1 4

IOP:SCDV 2 6(over

IOP:SCDX - All)

IOP:SCDP - 12

Table. 2.1: Growth capacity of the CP113.

The modular design of the CP113 means it can be easily adapted to different sizes of

switching center. Its current growth capability is shown in Table 2.1.

One of the two base processors operate as the master (BAPM) and the other as a spare

(BAPS). During normal operation the BAPM handles all operation and maintenance

functions and its share of the call processing function. If the BAPM fails, its functions are

handled by the BAPS instead.The call processors (CAP) deal only with call processing

functions. They form a redundant pool together with the BAPS. Even if one processor fails

(either a BAP or a CAP), the CP113 can thus still provide the full nominal load (n+1

redundancy). There is no CAP in the basic capacity stage.

The two buses to the common memory (BCMY0, BCMY1) transfer and save identical

information during normal operation. If a fault occurs in one of the functional units, it is

49

disconnected from the trouble-free units.The CP113 has a 2-level memory concept. This is

one of the main reasons for its high switching performance. A separate local memory

(LMY) is available to each processor, in addition to the common memory (CMY).

Distributing the data and programs between processor-specific memories and a common

memory for all processors results in short access times. The local processor memories

contain the dynamically relevant programs and the data which is only required by their own

processors. The common memory contains all the common data, as well as programs and

data which are not required very often.

The common memory also handles data exchanges between the processors. The stored

data is supervised in the CMY and the LMY on the basis of a check code. This code

enables 1-bit errors to be corrected automatically and all 2 bit errors to be detected, and

with a high probability it also enables greater bit mutilations to be detected.

The input/output controls (IOC) coordinate and supervise accessing of the CMY by the

input/output processors (IOP). The connection between each IOC and its associated IOPs is

set up by a separate bus system per IOC for input/output control (B:IOC). Up to 16IOps

can be connected to a B:IOC.

The IOCs and the IOPs have been designed so that they can assume responsibility for the

functions of the partner units if these fail. The redundant O&M data equipment (O&M

periphery) is always connected to different IOCs. If one IOC or the corresponding

input/output processors fail, all inputs and outputs are diverted via the partner IOC. (to or

from the redundant O&M and data equipment).

Base processor, call processors, input/output control

BAP, CAP and IOC are constructed with the same hardware components.They can

therefore all be described together. Each processor comprises:

Processing unit (PU)

Local memory (LMY)

Coupling logic (CL)

Common interface (CI)

50

The IOC additionally includes:

Interface for the bus system for input/output control (B:IOC)

The hardware components of the processor are connected together by means of a local bus.

This bus consists of 32 data lines and 32 address/control lines, and has an addressing

capacity of 4 Gbytes.

The processing unit (PU) is duplicated. This redundancy enables rapid error detection and

fault analysis, and thus prevents faults from spreading. The central feature of the PU is a

32-bit processor with a data width and an address width of 32 bits each. It executes the

system-specific software and the function-oriented user software. It also controls the data

flow to and from the input/output processors (IOP) in the IOC. PU is implemented as

CPEX module.

The local memory (LMY) consists of dynamic RAM chips. It has maximum storage

capacity of 32 Mbytes in the BAP, CAP and IOC (depending on the number of modules

and the size of the memory chips). The LMY is organized in the words with width of 32

bits. There are seven check bits for each word. The check bits generated and checked by

the cycle control card (implemented as CPCC module). The LMY is implemented as MUH

module.The LMY saves the data and the check bits in two separate memory areas. A

separate control is provided for each memory area.The coupling logic (CL) connects the

two Pus of the processor together. Its main function is to compare the processing results of

these PUs. If the coupling logic establishes a divergence between the two PUs, it disables

the common interface (CI) of the processor to the bus to the common memory ( B:CMY)

and resets the processor. CL is implemented as CPCL module.

The display/control panel of the coupling logic module has four hexadecimal displays for

visualizing information, as well as the some controls for the processor, namely reset button,

a BOOT button, a test switch and a diagnosis display switch.The processor is connected to

the two buses to the common memory via the common interface (CI). All common memory

accesses and all inter processor communication are effected via this interface. CI is

implemented as CPCL module.

51

In addition to the hardware components common to all the processor, the input/output

control (IOC) contains an interface to the bus system for input/output control (B:IOC). The

input output processors are connected to the local bus of the IOC via this interface. Like the

IOC, the input/output processors therefore address the various memory areas via the access

control. B:IOC is implemented as IOCIF module.

D

C

C

M

S

C

P

C

I

B

C

P

C

I

A

C

P

C

C

C

P

A

C

C

P

E

X

M

U

H

M

U

H

C

P

C

L

C

P

C

C

C

P

A

C

C

P

E

X

C

P

E

X

C

P

A

C

C

P

C

C

C

P

C

L

I

O

C

I

F

I

O

C

I

F

M

U

H

M

U

H

C

P

E

X

C

P

A

C

C

P

C

C

C

P

C

I

A

C

P

C

I

B

D

C

C

M

S

Module frame for BAP/IOC

DCCMS = Direct Current Converter Module

CPCIA = Common interface (A) Module

CPCIB = Common Interface (B) Module

CPCC = Cycle Control Module

CPAC = Access Control Module

CPEX = Processor Module

MUH = Local Memory Module

IOCIF = Bus Interface For IOC (B:IOC) Module

Module frame for processor and input/output control (F:P/IOC)

Bus to Common Memory

52

The bus to the common memory(B:CMY) connects all the processors (BAP,CAP,IOC)

both to one another and to the redundant common memory .The BCMY has been made

redundant to improve safeguarding . The two BCMYs operate in parallel and handle

identical information. They may operate asynchronously in exceptional situations(split

slate).The B:CMY has an addressing capacity of 4 Gbytes and a transmit data width of 4

bytes. The read cycles are $ bytes long. The write cycles are 4 bytes long. The write cycle

length is between 1 and 4 bytes.

The B:CMY operates according to a time division multiplex method with four time slots,

which can be used for information transfer. The four time slots are permanently assigned to

the four banks of the common memory .Since the time slot length corresponds to a quarter

of the memory cycle time , all four memory banks (MBY) can be addressed during each

time slot frame.

The B:CMY also handles inter processor communication (IPC). IPC cycles are not

implemented using the time division multiplex method . A memory cycle thus cannot be

incorporated in an IPC cycle.

The main functional blocks of the BCMY are as follows

Processor interface unit (one for each processor and input/output control)

B:CMY arbiter (one decentralized stage for every four processor or IOCs and one

central stage),

BCMY controller (one),

BCMY buffer (one),

Memory interface (one) and clock system (one).

The modulator design of the BCMY allows it to be adapted to any capacity stage of the

CP113.

6.3 Functions

53

Three essential functions of switching network namely speech path switching, message

path switching and changeover to standby are described below:

Speech path switching

The switching network switches single channel and broadcast connections with a bit rate of

64 Kbit/s and multichannel connection with nx64 Kbits/s. two connection paths are

necessary per single channel connection (e.g. from calling to called to calling party). For a

multichannel connection, nx2 connection paths are necessary. In broadcast connections, the

information is passed from one signal source to a number of signal sinks (no opposing

direction).

The coordination processors (CP) searches for free paths through the switching network

according to the busy status of connection paths stored at that moment in the switching

network’s memory. The path selection procedure is always the same and is independent of

the capacity stage of the switching network. During path selection, the two connection

paths of a call are always chosen so that they will be switched via the same space stage

section. A space stage section is a quarter of the space stage arrangement; with an SN:252

LTG, for example, this corresponds to half a space stage group SSG.

After path selection, the CP causes the same connection paths to be switched through in

both switching network sides of an SN. The SGCs are responsible for switching the

connection paths. In a capacity stage with 63 LTGs, one switch group control participates

in switching a connection path; however in a capacity stage with 504, 252 or 126 LTGs,

two or three switch group controls are involved. This depends on whether or not the

subscribers are connected to the same TSG. The CP gives every involved switch group

control a setting instructions necessary for the through-connection.

Message path switching:

54

A part from the connections determined by subscribers by inputting dialing

information, the switching network also makes connections between the LTG and the CP.

These connections are used to exchange control information; they are setup only once, and

then they are always available. For this reason, they are called semi permanent connections.

Via these same connections, the LTGs also interchange message without having to burden

the CP’s processing unit. In this manner, a separate line network for the exchange of

messages within an exchange is not necessary. Nailed-up connections and connections for

common channel signaling are made on a semi permanent basis as well.

Changeover to standby

All connections paths are duplicated, i.e. switched through in SN0 and SN1. This

provides an alternative route for each connection in case of failure.Figure 19 provides a

simplified illustration of the various alternative routes possible in capacity stages with 504,

252 and 126 LTGs. The connection paths are switched in the same manner over both

switching network sides (SN0 and SN1). The LTGs accept the incoming octets of the

effective connections (subscriber/subscriber connections) from only one switching network

side. In figure 19, the effective connections lead over SN0. Of note is the duplicated

routing between the time stage groups (TSG) and space stage group (SSG). This makes it

possible for the TSGs and SSGs to be individually switched over to standby. Switching

over to standby is implemented only if errors occur simultaneously in both switching

network sides. The effective connections are then lead over routed TSGs and SSGs of both

switching network sides 0 and 1. In the switching network capacity stage with 63 LTGs, it

is only possible to route the connections over SN0 or SN1.

If an error occurs in the switching network, the CP initiates corresponding measures for

switching over to standby and issues the corresponding messages. Changeover to standby

do not interrupt existing connections. Thanks to this duplication principle, all operational

measures are easily carried out without impairing traffic (e.g. adding new modules or

replacing defective modules).

55

Changeover to standby in the switching network capacity stage

7. REPORT

56

In the following we have presented the procedure that has been employed in providing new

user with a new subscriber number, providing him with different facilities that can

provided to a user, denying him with some of the facilities in case he is not eligible for few

of the provided ones. Moreover, the routing procedure has been illustrated. In the routing,

firstly the call is routed to the local exchange and then it is routed to the exchange specified

by the code in the dialed number.

Generally the procedure that is undergone is as follows:

The number without its local code is recognized at the local exchange.

It is checked whether the user can be availed with the facility that he has asked for.

if yes then the further steps are continued else an announcement is heard saying that

he is devoid of that facility

Then a code related to the local exchange is placed at one end of the number and at

the other end, the code related to the destination is placed

At the destination end, the local area code and the other code associated with the

number are removed and caller is directed to the destination number

In the process sometimes one of the routes may be busy. In those cases the callers

are directed through some other free route.

Thus the caller is routed to the destination number.

In OMT, sometimes alarms are raised due to different reasons owing to the failure of some

chords in the racks, or some link failure at any other exchanges connected to the present

local exchange.

Some other facilities like call waiting, call diverting, conference etc. can also be provided

to the user at user level. In conference kind of facilities a user is allowed to get connected

to more than one destination. Call diverting refers to diverting the call from one number to

other on the request of the subscriber. Call waiting is provided in order to make the user

aware of another call while he is busy with one. However, the tarriffing is due accordingly.

The entire above mentioned have been illustrated in the following presentation. This is

actual report regarding how all the above mentioned are put into act in an exchange.

57