AMRITSAR COLLEGE OF ENGG. AND TECH ,

AMRITSAR (143001)

A SIX MONTH TRAINNING REPORT

ON

DIGITAL ELECTRONIC SWITCHING SYSTEM (EWSD)

At

BHARAT SANCHAR NIGAM LIMITED (BSNL),

AMRITSAR – 143001 PUNJAB

Submitted to: Submitted by:

V.K. BANGA VARUN KAPOOR

H.O.D ECE Deptt 8TH SEMESTER

ACET , AMRITSAR Uni Rol no.6010404650

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College Rol no. 1106086

ACKNOWLEDGEMENT

I take this golden opportunity to express my sincere thanks to

Mr..N.k.Malhotra (divisional engineer, BSNL Katra Sher Singh,Amritsar).

Its give me immense pleasure to express my gratitude towards all esteemed engineers of

BSNL(Bharat Sanchar Nigam Limited, Amritsar) for their cooperation and constructive criticism ,

valuable guidance and constant encouragement.

I am greatly indebted to Er.Lakhwinder Singh ,SDE ( Sub Divisional Engineer, GRDM BSNL

Office) for their invaluable suggestion and guidance . I am highly grateful to them for providing the

required facilities which include the well-furnished labs, well working systems.Besides that there is

complete collection of all latest software technology. The software technology is also updated

regularly.

I am also thankful to all our friends for their help and cooperation. I express my deep sense of

gratitude towards my loving parents for their inspiring encouragement, great patience and unbound

affection.

It was a really good experience working in the institute and learning from such good and

knowledgeable people . I hope it would be really helpful to me in the near future.

2

Content

S. no. Topic pg no.

1). Company Profile 5

2) Introduction 8

3). Mechanical design introduction 9

4). Principal of Digital telephony 10

5). Appllications and capabilities of EWSD 11

6). Features of Analog subscriber 17

7). Features of ISDN subscriber 18

8). Block Diagram Of EWSD 21

9). DLU (Digital Line Unit) 23

10). LTG ( link Trunk Group) 26

11). SN (Switching Network ) 27

12). CP (Coordination Processor) 28

13). MB (Message Buffer) 31

14). CCS ( common Channel Signalling ) 31

15) System Panel ( SYP) 32

16). CCNC (common channel signaling control network) 33

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17). Mechanical Design of EWSD 34

18). Hardware Architecture 22

19). Software Architecture 37

20). LTG Functions 44

21). Call Set Up 47

22). Connection in ISDN 49

23). Dialog Mode : MML commands 54

24). Maintenance Function 60

25). MDF( Main Distribution Frame) 63

26). Power Plant 63

27). Risk Factors and Testing 68

28). Bibliography 70

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PROFILE OF COMPANY

The formation of Bharat Sanchar Nigam Limited (BSNL) on 1st October 2000 was one of

the landmark events in the history of Telecommunications in India. Today, BSNL is the

largest Public Sector Undertaking of the nation serving more than 34 million customers. It

has the responsibilities to improve already impeccable quality of telecom services,

expansion of telecom network, taking telecom services in all the villages and instilling

confidence amongst its customers.

VISION:

BSNL would like to be a high-tech customer oriented company emphasis on value addition.

MISSION:

To provide world class Telecom Services on demand using State-Of-Art technology for our

valued Customer at affordable price.

OBJECTIVES:

Provide Telephone in all villages in India by Dec 2003

Raise Telephone density to 7 by 2005 and 15 by 2010

Raise mobile towers density by 2010

Provide Bandwidth on Demand

Build Customer’s confidence though quality and reliable service

Provide world-class telecom infrastructure

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ASSETS:

Bharat Sanchar Nigam Limited has got fixed assets valuing more than Rs. 90,000 Crores

(US $ 20.64 billion), which are in the form of Land, Buildings, Cables, and Apparatus &

Plants etc.

REVENUE:

The Department of Telecom operations now known as BSNL has shown sustained growth

in the last 15 years. In its first year of operation as a Corporate, the anticipated growth rate

is 11%.

BUSINESS FIELD OF BSNL

The formation of Bharat Sanchar Nigam Limited (BSNL) on 1st October 2000 was one of

the landmark events in the history of Telecommunications in India. Today, BSNL is the

largest Public Sector Undertaking of the nation serving more than 34 million customers. It

has the responsibilities to improve already impeccable quality of telecom services,

expansion of telecom network, taking telecom services in all the villages and instilling

confidence amongst its customers.

BSNL mission is to provide world class Telecom Services on demand using state of the art

technology for their valued customers at affordable price.

Changing regulations, converging markets, competing technologies and ever demanding

customer needs have generated enormous additional opportunities for BSNL and so are

the challenges. There is a gradual shift in demand from telephone centric to data centric

environment, which has defined a new paradigm in telecom business.

The company with a sound financial base is ready to face the impact of the upcoming

competition. BSNL has received an overwhelming response to its simultaneous launch of

GSM cellular mobile Telephone services (CMTS) across the country. The Voice over IP

(VoIP) will be introduced shortly between six cities in the country. The introduction of DSL

technology in the access network will be another solution to meet the demand for high

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bandwidth considerably. Other technological innovations in the form of Managed Leased

Line Networks (MLLN), LMDS, DLCs &

RLC in the access network are in different phases of implementation. Commissioning of

DWDM in the main routes through "Sanchar Sagar Project" has laid the foundation for the

formation of National Information Super Highway. Introduction of Internet Telephony

("WEBFONE") has proved the BSNL commitment towards "Providing World-class Telecom

services at a very affordable price to our valued customers."

The company is committed to provide a combination of products and professional services

with a wide choice of end-to-end solutions and self care to meet the aspiration of the

customers and to give them the satisfaction.

SERVICES OF BSNL

1. Land Line Telephone

2. Mobile Communications

3. Internet Facilities

4. Leased Line

5. ISDN (Integrated Services Digital Network)

6. MPLS Based IP-VPN Services

7. INET

8. WLL (Wireless in Local Loop)

9. TELEX/TELEGRAPH

10. HVNET (High Speed Satellite Based VSAT Network)

11. RABMN (Remote Area Business Management Work)

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EWSD

DLU/LTG

CCNC

CP

SN

INTRODUCTION

User software Software Architecture

Operating system

Hardware

Hardware Architecture

8

Mechanical Design

EWSD from Siemens is a powerful and flexible digital electronic switching system for public

communication networks. It meets all the current demands and is equipped to meet those

of the future. Since being launched on the world market in 1981, EWSD has gained an

excellent reputation by virtue of its responsibility, cost-effectiveness and wealth of features

for subscribers and operating company.

EWSD is one system for all applications in terms of size, performance, range of services

and network environment. Its modularity and the transparent nature of its hardware and

software allow EWSD to adapt to any network environment. One of the factors contributing

to its flexibility is the use of distributed processors with local control functions.

EWSD allows the telephone network to evolve into an integrated services digital network

(ISDN). The ISDN simultaneously handles the switching and transmission of telephone

calls, data, and text and images reliably and economically, in accordance with user needs.

Other feature of EWSD is that it compiles with international standards and

recommendations lay down by CCITT and CEPT. The participation of Siemens engineers

in the study groups of these organizations guarantees a good flow of information between

standardization, development and field applications.

EWSD is kept constantly up-to-date through the support and ongoing development work of

highly-skilled teams equipped with powerful set of SW tools. The range of features is

continually being improved to satisfy future requirements as well, e.g. broadband services.

New technologies can be incorporated in EWSD without altering its system architecture.

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APPLICATION & CAPAILITIES

EWSD offers optimal solutions for a wide range of future oriented applications. The

flexibility of the system and the high capacity of each exchange have particularly positive

effects:

EWSD can be adapted easily and optimally to the requirement of the operating

company and to the conditions of specific network.

One EWSD exchange has a switching capacity of up to 25200 erlangs and can handle

over 1000000 BHCA.

The main application and capabilities are illustrated and outlined below:

Digital Line Unit

Local Exchange

Transit Exchange

Local/transit Exchange

International Gateway Exchange

Value Added Services

Mobile Switching Centre

ISDN CCS7 Centralized O&M

Operator Service System

Rural/container Exchange

EWSD

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DIGITAL LINE UNIT:

The digital line unit (DLU) is the functional and on which the subscriber line are terminated.

The lines may be analog or digital i.e. equipped for ISDN. All DLUs are connected to the

other EWSD subsystem via a uniform interface standardized by CCITT (primary digital

carrier, PDC). This allows the either DLU to be the installed in the exchange itself or

alternatively as remote switching units.

LOCAL EXCHANGE:

Local exchanges service the subscribers within a particular area e.g. a district of a city or a

locality. They switch incoming traffic to and outgoing traffic from the connected subscriber.

The number of subscribers connected to an EWSD exchange can be as low as a few

hundred or as high as 250000

TRANSIT EXCHANGE:

At node points in the telephone network transit exchanges connect together trunks to and

from other exchanges up to 60,000 incoming outgoing or both ay trunks can be connected

to EWSD transit or long distance exchanges.

LOCAL/TRANSIT EXCHANGE:

These exchanges handle transit or long distance traffic as well as incoming and outgoing

local traffic. Any number of subscriber lines and trunks can be combined within the

maximum traffic handling capabilities of the exchange. Within the above-mentioned local

and transit exchange capacity limits, any combination of subscriber lines and trunks can be

connected, as well as the limit of 25,200 erlangs is not exceeded.

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INTERNATIONAL GATEWAY EXCHANGE:

EWSD handles all special functions in international gateway exchange such as

international signaling system echo compensation on intercontinental connections and

satellite links and inter administration revenue accounting static’s. These functions can also

be integrated in national exchanges if necessary.

MOBILE SWITCHING CENTRE:

Modern networks for mobile radiotelephones have a cellular structure to enable economic

usage of the available frequencies over the entire area. A radiotelephone user moves from

one radio zone to the next, transmitter, and receiver are automatically switched over at the

same time, the relevant EWSD mobile switching centers automatically pass or the call data

on the user equipment (operational status, directory number etc). This mean that any

mobile subscriber can always be reached under the same directory number, the caller calls

not have to know the current when about of the person being called. The mobile switching

center can serve the up to 65,000-radiotelephone subscriber.

RURAL/CONTAINER EXCHANGE:

For sparsely populated areas, there are rural exchanges serving from several hundred to

7,500 subscribers. Rural exchanges-complete with MDF, power supply and air-conditioning

units-can also be supplied installed in containers. A containerized exchange contains up to

6000 subscriber line terminations. Container exchanges have the same hardware and

software components as normal exchanges.

OPERATOR SERVICE SYSTEM:

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Digital switchboards are available in EWSD to establish operator-assisted calls and to

provide special subscriber services.

The operator service system (OSS) is microprocessor controlled. It distributes incoming

service requests to the attended operator positions of the respective function-specific

groups. The system offers calls booked in advance to the operators at the requested time.

Other automatic functions available in OSS reduce the workload of the operators

CENTRALIZED OPERATION & MAINTENANCE:

Both local and centralized operation and maintenance center (OMC) can operate and

maintain EWSD exchanges. Operation and maintenance (O&M) of several EWSD

exchanges from one OMC permits rational assignment of personnel, flexible adaptation to

the operating company’s organization structure and central data storage. The operators

work interactively, using O&M terminals. An easily learnt man-machine language and

access authorizations ensure error-free inputs.

COMMON CHANNEL SIGNALLING SYSTEM NO.7:

EWSD exchanges employing the powerful CCITT common channel signaling system no.7

(CCS7) are equipped with a common channel signaling network control (CCNC). One

CCNC can handle the signaling for up to 254 signaling channels. The functions performed

by CCNC cover both those of a signaling point (SP) and those of a signaling transfer point

(STP).

INTEGRATED SERVICES DIGITAL NETWORK (ISDN):

ISDN allows switching of connection paths and transmission of information for various

services via a single network. This brings significant technical, operational and economic

benefits both for the operating company and for the subscribers.

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Network terminations and terminal adapters are available for terminating the subscriber

lines. Network and service networking equipment is provided for the transmission from

today’s single-service networks to the ISDN, e.g. packet server module (PSM).

VALUE ADDED SERVICES:

Value added services (VAS) are communication services that involve storage and

processing functions. The necessary equipment is located in a central position in the public

network or in the private service centers. Examples of central network-based VAS include

access to text and databases, e-mail, fax, voice messaging and conversion and service

networking. EWSD in ISDN offers ideal conditions for all VAS.

FEATURES OF EWSD

With its wide ranging and versatile features, EWSD meets all the demands required for a

modern telephone system. This section contains lists of typical system features and

features of analog and ISDN subscribers. A few of these features are given below:

SYSTEM FEATURES

EWSD provides the operating companies with many beneficial features, which contributes

to the universality, flexibility, and performance of the switching system. The scope of these

system features and the ease with which they can be implemented demonstrates the

advanced technical level of the EWSD switching system.

INTEGRATED SUPERVISION STRATEGY:

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EWSD itself automatically detects faults, malfunctions in both the hardware, and initiates

corrective measures. For this purpose the main part of the system are duplicated. The

integrated supervision strategy includes in service supervision, fault indication, fault

analysis procedures, and fault diagnosis.

INTEGRATION INTO EXISTING NETWORK:

EWSD can be integrated into any existing telephone network. Great importance was

attached to the flexibility of the relevant parameters right from the start. E.g. numbering,

zoning routing and metering is predestined.

ALTERNATIVE ROUTING:

An outgoing connection can be set up via a first choice route or via one up to seven

alternative routs. The number of available routes to a given destination can be varied

according to the time of day.

CHARGE REGISTRATION:

EWSD has two basic operations for the flexible registration of telephone charges

1. Time pulse metering (single, multiple or periodic pulse metering)

2. Various forms of automatic message accounting (CDMA, LAMA)

Both methods can be used optionally or simultaneously in EWSD exchange.

TRAFFIC MEASUREMENT:

Traffic data recording comprises registration, recording and supervision. The registration of

subscriber data is started and carried out by the call processing programs. Operations and

maintenance programs handle the output of selected data. The O&M programs are started

15

by MML commands and can be loaded to the CP main memory as required. EWSD does

not need any additional equipment to record traffic data and monitor the grade of service.

Optional programs are available for traffic observation and traffic observed and traffic

structure measurement.

DATA BASE MANAGEMENT:

This includes the maintained correction and expansion of the database with suitable

software support.

ISDN:

In existing EWSD exchange ISDN features can be incorporated as required in small stages

parallel to the conventional features. The modular software architecture allows the range of

features to be modified easily. As a result an operating company can tailor its facilities and

service offering to the needs of its customers.

FEATURES FOR ANALOG SUBSCRIBER

The features for analog subscriber enable the operating company to offer its customers the

desired convenience and provide attractive, readily acceptable functions for the telephone

services.

ABBREVIATED DIALING:

This popular feature allows the subscriber to assign abbreviated number then needs to be

dialed to set up the call.

CALL WAITING:

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A subscriber already engaged on a call is notified that there is another call waiting. He can

enter the new call and if required, switch between the old connection and the new one.

CALL DIVERSION:

When absent from the telephone, a subscriber can have all incoming calls diverted to

another destination. Either the destinations can be a recorded announcement, a service

position or another subscriber’s number.

PREFERENCE CATEGORY DURING CATASTROPHE:

A certain subscriber, for instance those to work for the public emergency services, can be

assigned a higher priority. If a catastrophe occurs, only the subscribers are able to make

outing calls, this feature does not restrict incoming calls. This feature guarantees the

communication services for priority subscriber during a catastrophe, where this

communication may be essential for the saving of lives.

FEATURES FOR ISDN SUBSCRIBERS

ISDN adds substantially new functions to the range of features. They allow the operating

company to provide subscribers with function and capabilities, which cannot be

implemented with conventional, telephone system.

ISDN ACCESS:

In ISDN EWSD provides main station lines and small and medium sized PBXs with basic

access arrangements each offering two B channels and one D channel. Medium sized and

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large PBXs can be connected to EWSD via The primary rate access. The basic access and

primary rate access are in accordance with CCITT recommendations. Up to 16 sockets and

up to 8 terminals can be connected to a basic access interface. The terminals can be

unplugged, plugged at any of the sockets, and dialed directed by means of individual

addresses. Convenience is increased by the capability for simultaneous multi-service

operation with service indicators and charge of service during calls

SIMULTANEOUS MULTI-SERVICE OPERATIONS:

The subscriber has the option of using two services in parallel, for example transmitting a

fax and holding a telephone conversation at the same time. Both connection can be

directed to different destination and complete the independent of one another.

TRANSFERRED CHARGE CALLS:

Subscriber B can agree to accept the charges for a call that would otherwise be charged to

the A subscriber. The B subscriber can accept charges on a permanent or an ad-hoc basis.

In the latter case the subscriber is asked whether the charges will be accepted on each

occasion.

DISPLAY INFORMATION:

For example the number of a calling party or the status of a call can be displayed. See fig

on next page.

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19

Access arrangements of an EWSD exchange in ISDN

EWSD ISDN Local Exchange

Service modules

NT

NT

PBX

PBX

NTY

TA

Analog telephone

Digital telephone

Facsimile

Text

Image Transmission

Data processing

Integrated Voice & Data Terminal

Conventional Terminals

Terminals as above

Terminals as above

Telephone Network

ISDN

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HARDWARE ( block diagram of ewsd)

Distributed controls in an EWSD exchange

Coordination

Common channel signaling

AccessSwitching

EM

OMT

CP

CCG

MB

SYP

SNDLU LTG

LTG

SGC

CCNC

21

The hardware represents the physical components of a system. In a modern switching

system such as EWSD the hardware is modular, reliable, flexible and of a high quality. It

also allows the adaptation to new technologies and rational manufacturing (including in

country of use). This is all achieved by:

Clear & easy-to-understand, future-proof hardware architecture

Modular mechanical design

Use of the appropriate hardware technologies and

Painstaking hardware quality assurance

HARDWARE ARCHITECTURE

The hardware architecture permits many flexible combinations of subsystem and has

clearly-defined interfaces. This forms the basis for cost-effective use of EWSD in all areas

of the broad spectrum of applications. Functions determined by the network environment

are handled by the digital line unit (DLU) and the line/trunk group (LTG). The common

channel signaling network control (CCNC) functions as the message transfer part (MTP) of

signaling system No.7. The function of the switching network (SN) is to interconnect the

lines and trunks of the exchange in accordance with the call requirements of the

subscribers. The controls of the subsystems involved carry out practically all the tasks

arising in their area independently (e.g. the LTGs handle digit reception, charge

registration, supervision and other functions). Only for system-wide and coordination

functions, such as routing and zoning for example, do they require the assistance of the

CP. Fig. above shows how the most important controls are distributed throughout the

system. This principle of distributed control reduces the necessary coordination overhead

and the necessity for communication between the processors and contributes to EWSD’s

very high dynamic performance standard. The flexibility inherent in distributed control also

makes it easy to introduce and modify features and to assign features to specific

subscribers.

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For inter-processor communication, the switching network sets up 64 kbps connections-in

the same way as connections between subscribers. But the connections between the

processors remain established; they are therefore referred to as semi permanent

connections. This avoids the necessity for a separate inert-processor control network.

Exchanges of all types and sizes can be implemented with just a few types of subsystem

and the appropriate software

When the hardware architecture was designed, provision was made for use in ISDN right

from the start. Basic considerations here were:

Ability to freely combine analog telephone lines and ISDN lines in the same exchange,

Facilities for subsequent incorporation of ISDN service features into EWSD exchanges

already in operation.

The features that predestine EWSD for use in ISDN are:

A fully-digital system right from the outset,

Analog-digital conversion on a per-line basis,

Distributed control,

Common channel signaling in accordance with CCITT No.7.

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Digital Line Unit

INTRODUCTION

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

The DLUs can be operated locally in an exchange or remotely.

The DLUs are connected to the switching network via LTG. A DLU is connected to and

LTG by 2 Mbps Primary Digital carriers (PDC). However the local DLUs (the DLUs located

in the main exchange) are connected to the LTG by 4 Mbps carriers.

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

CCITT is used for singling between a DLU and the group processor (GP) in the two LTGs.

Remote DLUs are installed in the vicinity of groups 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 quality.

The following are the important DLU features:

Connection capacity of a single DLU: up to 952 subscriber lines

Traffic handling capacity : up to 100 Erlangs

Connectivity : Analog subscriber lines with

- Rotary / DTMF dialing

- Call charge indication with 6/12 kHz

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As well as access lines for

- coin box telephones

- analog PBX with / without DID

- Small and medium-sized digital PBXs

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 (LTGG) via one, two or four PCM30 multiplex lines

(primary digital carriers, PDC). The local connection to LTGG can be realized via two

4096-kbps multiplex lines.

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Maximum number of channels available for transmission of user information

between a DLU and two LTGs is 120.

Common channel signaling (CCS) between the DLU and the LTGs. TSI6 on PDC0

and PDC2 used for this purpose.

High operating reliability

- Due to the connection of the DLII to two LTGs

- Duplication and load sharing of DLU modules handling central functions.

- 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 TU) for, automatic and manual testing of subscriber line

circuits, subscriber lines and analog telephone sets .

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 up to six

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

alone Service Controller) for emergency operation.

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

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subdivided into a left-hand and a 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 cards,

• Ringing & Metering Voltage Generation,

• Bus system comprising of

- Control Network for processors

- 4096-kbitsls network for speech signals

• Peripheral cards which include Line cards and Test cards,

• DCCs, i.e., Direct Current Converters

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) &

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(d) Two bus distributor modules (BD).

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

housed together in a module frame.

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

upper shelf (shelf 0) of the module frame and

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

lower shelf (shelf 1).

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

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

possible via the other DLU system.

DLU CONTROLLER

For security reasons and to increase throughput, there are two DLUCs 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 the DLUC. The DLU-

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

with their own microprocessor are addressed through this control network.

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

directly for the transfer of commands and data from DLUC

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

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

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DIGITAL INTERFACE UNIT FOR DLU (DIUD)

The DIUD has two interfaces for the connection of two PCM3O multiplex lines (PDCs)

connecting the DLU with the LTG. Either balanced or coaxial cables 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 functions of DIUD:

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

(DIUDO takes the control information from PDCO, DJUDI 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 partner DLUC is inserted in channel 16 of the

same PDC and transmitted to the LTG.

2. Provides the interfaces to a DLU-internal 4096-kbitls network to the individual

shelves. The user information is distributed to and from the SLM modules via this

4096-kbitfs network.

3. Derives a signal for synchronization if the clock generator from the line clock of the

PDC.

4. Performs test and supervisory routines and detects any occurring errors.

5. The channel contents of the’ PDC with CCS are forwarded to the even numbered

channels of the 4096-kbitls network, the channel contents of the PDC without CCS

to the odd channels.

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6. A test loop is switched via the DIUD for the cross office check (COC) conducted by

the LTG.

7. LEDs in the module faceplate indicate the operating mode of the DIUD and the

PDCs.

BUS DISTRIBUTOR MODULE WITH CLOCK GENERATOR (BDCG)

The clock generator (CG) generates the system clock of 4096-khz required by the DLU and

the associated frame synchronization pulse. For security reasons the clock generator is

also duplicated. The two clock generators work according to the masterslave principle.

Under normal operating conditions the clock generator designated as the master is active

while the slave generator is in standby mode.

The master supplies both DLU system with clock signals. If the master fails, the system

switches over to the slave generator which then supplies both DLU systems with clock

signals.

The clock generator receives a synchronizing signal from the DIUD in the same shelf the

DIUD derives this signal from the line dock of the related PDC.

RINGING & METERING VOLTAGE GENERATOR

The ringing and metering voltage generator (RGMG) generates the sinusoidal ringing and

metering voltages required in the DLU for analog subscribers, as well as a synchronize

signal for ringing the subscribers.

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Several different frequencies can be set for the ringing voltage by means of switches.

Another switch allows two different voltages to be set for each frequency selected.

Two different frequencies (12 or 16 kHz) can be set for metering voltage by means of a

switch. The metering voltage cannot be changed.

The ringing and metering ac voltage are monitored for undervoltage. If the voltage drops

below the minimum value permitted, art alarm is signaled.

Each BD unit can switch over to another RGMG which then supplies the entire DLU with

ringing and metering voltage.

From each RGMG, a ring bus system is used for the distribution of ringing and metering

voltage.

RGMG0 supplies ringing and metering voltage to all the mounting locations for SLMs in the

left-hand half-shelves (SLM0...7) through the ring bus system 0 and the BG units in these

half-shelves. RGMG supplies ringing and metering voltage to all the mounting locations for

SLMs in the right-hand shelves (SLM8.. 15), through the ring bus system I and BD units in

these half-shelves during normal operation. If a fault occurs in one of the RGMGs, the other

RGMG takes over the entire load.

The ringing voltage is fed to the BG units over a short-circuit safety circuit and is distributed

unamplified to the SLM mounting locations in the relevant half- shelf.

The metering voltage is forwarded in an amplifier with balanced high- impedance input in

the BD units and distributed unbalanced and with low impedance in the relevant half-shelf.

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TEST UNIT

The test unit (TU) consists of two modules – FMTU and LCMM. These two modules can be

plugged into mounting locations for SLMs in the module frame with central units, i.e.

F:DLU(A).

The test unit is provided in the DLU to test subscriber telephones, subscriber lines and

subscriber line circuits (SLCs). It can be connected to each subscriber line or each SEC via

a test bus. The test relays for metallic access to the items to be tested are an integral part

of the SLCs.

Testing of the subscriber lines connected to the DLU is controlled from the line workstation

(LWS). The LWS can be located either centrally in the OMC or locally in the exchange. A

special user program (TLFI) in the GP of the LTG acts as the interface between the TU and

the LWS. The program TLFI controls the TU therefore the subscriber line test in

accordance with the inputs. During such a test, the GP and TU exchange commands (GP

to TU) and results (TU to GP) via CCS channel pair 16 of one PDC and via one DLUC.

In addition to the LWS, the subscriber link measuring system (SULIM) can also be used to

control testing of analog subscriber lines. The SUI.IM measuring boards’ arc located at the

DLU site, in exchange or in the OMC.

The user program TLFB in the OP of the LTG acts as the interface between the TU and the

SULJM measuring boards.

33

STAND-ALONE SERVICE CONTROL (SASC)

During emergency operation the stand-alone service control (SASC) is required in remote

DLUs for the communication between the connected analog, ISDN and CENTREX

subscribers. SASCs are also used in each DLU of a remote control unit (RCU).

EMERGENCY SERVICE EQUIPMENT FOR PUSH-BUTTON

SUBSCRIBERS (EMSP)

DLU can be equipped with an EMSP instead of an SLMA. Normally a maximum of two

EMSPs can be provided. Each EMSP contains THREE code- receiver circuits.

Under normal operating conditions an LTG receives the dialed information from DTMF

subscribers and evaluates it. In emergency service, pushbutton receivers are required in

the DLU itself for these subscribers. These pushbutton receivers are contained in the

EMSP modules.

EXTERNAL ALARM SET

The external alarm set (ALEX) is used to relay alarms from external devices (e.g., air

conditioning, power supply, fire extinguishers etc.) to the SYPD. Minimum one ALEX

module is required per remote cluster of DLUs. The ALEX can connect up to 16 external

alarms to the main exchange.

A specific fault printout can be output by the system for every external DLU alarm. The

commands for defining these fault printouts is contained in the MMN for SYP (register

INTRO). The same document also describes the level definition of these alarms. The pin

assignments for the ALEX are described in MMN for DLU.

34

DIRECT CURRENT CONVERTERS

The DLU power supply is decentralized. For each half-shelf in the module frame there is a

separate direct-current converter module (DCC). If a DCC fails, the consequences are

relatively minor, as only one half-shelf is affected.

The DCC modules supply all the operating voltages required in the shelf (inc1uding the

voltages required for any range extensions). The voltages generated are monitored for

undervoltage, and some also for overvoltage. If the specified tolerances are exceeded, an

alarm is triggered and the dc converter is disconnected electronically. All voltage outputs of

the DCC modules are short-circuit protected.

The voltage for the two DCCs is a shelf is fed via a common fuse in the fuse panel. The

exchange voltage supplied is unfiltered.

The voltage for the subscriber Tine modules (SLM) in each shelf is fed via a fuse in the

fuse panel. As far as the power supply is concerned, the subscriber line modules are

termed load circuits. The voltage supplied is filtered.

35

LINE/TRUNK GROUP

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).

36

CONFIGURATION TYPES

Different possible configurations for an LTG are as follows:

With digital transmission link (primary digital carrier, PDC)

- For digital line unit (DLU) operating at transfer rate of 2048 kbit/s. DLUs

can be used to connect analog as well as digital subscribers (e.g. with

PDC at 2048 kbit/s; ISDN basic access BA for ISDN subscribers and small

ISDN PBXs). When connected via PDC, the DLU is generally operated as

a remote unit with respect to the EWSD exchange.

- for digital trunks with transfer rate of 2048 kbit/s.

With digital transmission link for local operation of DLUs (i.e., DLUs within the main

exchange) at transfer rates of 4096 kbit/s

With primary rate access (PA):

For medium size and large ISDN PBXs (ISDN subscribers with PA) operating at

transfer rate of 2048 kbit/s.

LTG TYPES

Different hardware versions of’ LTGs exist for the various configurations above.

37

LTG (B-function) for DLU arid 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 (with 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 or without MFC. The transfer rates are 2048 Kbit/s

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

versa is 8192 Kbit/s (8 Mbps). Each of these SDCs has 128 time slots of 64 Kbit/s out of

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

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

images).

Messages are used for inter processor communication in the EWSD system, e.g., in the

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

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

Line/trunk groups can operate with all conventional signaling systems and can therefore be

easily integrated into any switching system. Signaling is the communication between

exchanges. Analog user information and analog signals are digitized by means of a signal

converter, multiplexer (SC/MUX) outside the EWSD exchange.

38

LTG FUNCTIONS

The main functions of the LTG are

(a) Call processing functions include:

- Receiving and evaluating signals from the trunk and the subscriber line

- Sending signals

- Sending audible tones -‘

- Sending messages to the UP 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 8 Mbps standard interface to the SN

- Through-connection of messages and user information

(b) Safeguarding functions include:

- Detecting errors in the LTG (without external test equipment)

- Detecting errors on the connection paths within 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 range of an error (e.g.,

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

- Exchanging routine test messages with the CP, so that the CP can detect a faulty

LTG if the LTC itself is not able to send error messages.

39

(c) Administrative functions include:

- Sending messages to the CP for traffic measurements and traffic observation -

- Switching of test connections .

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

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

fur transmission measuring (ATE:TM).

- Indicating important information

- (E.g. channel assignments) to the functional units

- Creating, blocking, and releasing devices via MML commands.

FUNCTIONAL UNITS

The Line/trunk group LTGG is made of following functional units:

Functional units in the Line/Trunk unit (LTU)

Functional units in the signaling unit (SU)

Group switch and interface unit (GSL)

Group processor (GP)

LINE/TRUNK UNIT

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

units. The purpose of these functional units is to adapt connected lines to the internal

40

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 (SIHO), 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 and GP.

The functional units listed below can be plugged into the LTU:

1. (A) Digital Interface Unit (DlU)

Digital interface unit (DIU) is used for connection of remote DLU, PA, digital trunks (up to

four digital interface units (DIU30, i.e. 2 Mbps) per LTGG); and for connection of external

test equipment, such as the automatic transmission measuring and signaling testing

equipment (ATME) and the trunk test equipment answer unit (TTE/AU). The signaling

methods used are channel associated signaling (CAS) and common channel signaling

(CCS).

In EWSD, an (external) digital announcement system (DAS) is connected to a DIU on a

single PDC. With the DAS, the operating company can store variable or permanent

announcements and output them on a channel specific basis. A DAS is connected via a 2

Mbps transmission link. The DAS consists of a base unit with speech memory cards for

announcements. The number of announcements can be increased through the use of an

expansion unit containing additional speech memory cards.

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

41

Local DLU interface module B (DIU:LDIB) is used for connection of local DLU]. In the

most common application, each LTGG has two DIU:LDIB, each DIU:LDIB having 60

channels on the 4096 Kbit/s transmission link to the DLU. Other configurations, e.g.

combinations of local and remote DLUs connected to the same LTGG are possible. A

DIU:LDIB replaces two 2048 Kbit/s transmission links with a 4096 Kbit/s transmission link.

The DIU:LIB of the LTGG communicates with the functional unit DIU:LDID in the DLU. The

signaling method used is common channel signaling (CCS).

2. Conference unit, module B (COUB)

The conferencing unit occupies the slot reserved for LTUs hence, is configured as an LTU.

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

units can connect upto 8 channels (e.g. 8 subscribers). It is also possible to cascade two

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

3. Code receiver (CR)

The following type of Code receivers can he used in the LTU if the capacity for CR in the

SU has been exceeded

- Multi frequency code receivers (CRM)

- Code receivers 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.

4. Automatic test equipment (ATE)

42

The ATE is used in one of two variants.

The automatic test equipment 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 demand testing of trunks with the trunk workstations (TWS) and serves as

director or responder within the ATME2 when testing international trunks. The AT’ME2 is

specified by CCITT. The ATE:TM consists of the module ATE:TM.

Signaling Unit

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

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

Tone Generator (TOG)

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

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

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

requiring them.

Code receiver (CR)

Depending on the type of LTG, the SU contains code receivers for push-button dialing i.e.

DTMP dialing (CRP) and/or for multifrequency code receivers (CRM) for trunks with

43

channel associated signaling (CAS). The CRP or CRM is assigned to DTMF subscriber line

of MFC trunks only for the duration of the digit input.

Receiver module for continuity check (RM:CTC)

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

continuity check (RM:CIC) 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 sends signaling characters to the GP via SIHI. SPHO/I

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

GROUP PROCESSOR

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

the functional units of the LTG and comprises the following individual modules –

1. Clock generator and signal multiplexer (CGSM)

2. Processor memory unit (PMU)

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

44

1. CGSM Module (Clock Generator and Signal Multiplexer)

The clock generator and signal multiplexer (CGSM) in the GP is made up 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 receives the clock pulses supplied from-both via the GSL (LIU part). Using the

supplied frame mix bit-(FMB), the CG part synchronizes the LTG clock with the SN clock.

To do this, the GSL derives the synchronization pulses SYNI from the FMB on an SN-

specific basis (SYN1-0 for SN0, SYNI-1 for SNI). The CG part selects one of the two

syncronization pulses SYNI and synchronizes the LTG clock to this pulse.

The synchronization pulses SYN1 are monitored by the CG part. An alarm is generated if

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

with SYN1 is also monitored. The CG Part sends alarm data to the signal buffer of the

PMU. Alarm data includes:

- Alarm in the event of synchronization failure

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

- Indication of which synchronization pulse is currently being used

It is also possible to transmit loop-back bits for test purposes from the signal buffer of the

PMU, the CG part also receives the control data for:

- Selection of synchronization pulse SYNI 0 or SYNI I

- Alarm test/alarm reset with reference to transfer rates 2048

- Setting loop-back bits for test purposes

45

All other clock pulses and synchronization signals required for the LTGG are generated

internally by the CG part of the GP. It is also the task of the CG part to monitor the PMU

and, in the event of a supply voltage failure, to reset the PMU.

The MCH part sends and receives messages to and from the GSL on the MCH. MCM1

goes to the LIU part of the GSL; MCHO comes from the LIU part of the GSL.

The SMX part receives the serial signaling data on SIBO from the signal buffer of the PMU.

It distributes and transmits these data to the LTUs and the SU on SIHO and adjusts the

timing accordingly.

The serial data arriving from the LTUs, the SU, the GS and the LIU are received by the

SMX part on SIHI; the SMX part adjusts the timing and sends the combined data lo the

signal buffer of the PMU on a 2048 Kbit/s highway (SIBI). The data can also be filtered, if

necessary. The signal buffer forwards the data to the PMU, where they are processed with

the help of the GP software and (if applicable) buffered.

46

SWITCHING NETWORK (SN)

The EWSD switching network (SN) consists of time stages and space stages. In time

stages, octets to be switched change time slot and highway according to their destination.

In space stages they change highway without changing time slots.

The parameters of time & space stages (4:4, 16:16, 8:15, 15:8) always represent the no. of

8 mbps highways, which have128 channels each. Connection paths through the time and

space stages are switched by the switch group controls (SGC) in accordance with the

switching information from the CP. The SGCs respond to the commands from CP. The

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

exchange of data between the distributed controls.

In its maximum configuration, the EWSD SN connects 504 LTGs, has a traffic handling

capacity of 25200 erlangs and contains only 7 different type of module. The SN can be

expanded in small stages by adding plug-in modules and cables and if necessary by

assigning extra racks.

The switching network is always duplicated (planes 0 &1). Each connection is switched

simultaneously thro’ both planes, so that a standby connection is always immediately

available in the event of a failure.

In digital switching networks, the octets being sent in two directions between the calling and

called subscribers are transmitted separately. This corresponds to a 4-wire connection in

analog systems.

FUNCTIONS

47

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 party and from 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 processor (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

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 SOC’s 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 he subscribers

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

setting instructions necessary for the through connection. These setting instructions always

have the same data format.

48

An SGC receives the setting instruction from the CP via the message buffer unit

MBU:SGC, the secondary digital carrier SDC:SGC, and its dedicated link interface module

LIM. The commands and messages between an SGC and the CP are exchanged via an

LIM. The SGC calculates the setting data using the call processing programs and service

routines. The SGC loads the data into registers in the hardware controller (HWC) of the LIM

and, via the l-IWC, controls the setting of desired connection paths in the time and space

stage modules (TSM and S SM).

MESSAGE PATH SWITCHING

Apart 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 semipermanent 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 semipermanent basis as well.

CHANGEOVER TO STANDBY

All connection 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 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.

49

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).

50

COORDINATION PROCESSOR (CP)

The coordination processor (CP) handles 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 and error messages, alarm treatment, error detection and error neutralization

and configuration functions,

Handling of the man-machine interface.

The CP113 is a multiprocessor, which handles the database as well as of EWSD

exchange. Its capacity can be expended in stages as per requirement. It has call handling

capacity of over one lakh BHC. In the CP113 two or more identical processors operates in

parallel with load sharing principle. The rated load of n processors is distributed among n+

1 processor. This means that if one processor fails, operation can continue without

restriction.

The CP113 has two level memory concepts. This is one of the main reasons for its high

switching performance. A separate level memory is available to the common memory. The

local processor memory contains the dynamically relevant programs and the data, which is

only required by their own processors. The common memory contains all common data as

well as program and data, which are not required very often. This arrangement results in

short access time.

The main functional units of the multiprocessor are as follows:

Base processor (BAP) for O&M and call processing,

Call processor (CAP) for call processing only,

Common memory (CMY),

Input/output controller (IOC),

51

Input/output processors (IOP).

Fig> coordination processor cp113

1

Periphery, input/output devices, external memory 0

BEU

IOPIOPIOP

BAPUMU

52

MESSAGE BUFFER:

It is the interface between CP and the group processors (GP) in LTG and SGC in the SN.

The IOP: MB is the interface between Cp and MB. Addresses all connected devices,

cyclically.

The MB is subdivided into message buffer groups MBG. An MBG is made up of message

buffer units (MBG). LTG is connected to MB via an interface MBU; SGC is connected to

MB via MBU; SGC through SN. For security reason MB is duplicated (MB. 0&MB 1). The

message buffer (MB) co-ordinates between the CP, the SN, the LTG, and the CCNC and

controls internal message exchange.

CENTRAL CLOCK GENERATOR (CCG):

In an EWSD exchange, the clock generation, synchronization and distribution of timing

signal are done by central clock generator (CCG). A view of vital roll in the exchange, the

CCG is always duplicated i.e. CCG (A) 0 and CCG (A) 1. The CCG is extremely accurate

(10). It can, however, be synchronized even more accurately by an external master clock

(10). Out of two CCGs, one is always switched as master and the other as slave. Only the

master CCG supplies the connected equipment i.e. message buffer (MB), coordination

processor (CP) and external clock distributors with synchronization clock.

The slave CCG, however, controlled by the master CCG, operates in face synchronism.

This ensure that in the event of

Malfunction or failure of master CCG, the master /slave roles can be switched over

immediately and automatically and thus clock supplies remain uninterrupted. It can works in

synchronous mode operation, i.e. with two external reference frequencies per module

CCGXXA and in plesiochronous, mode operation without external reference frequencies for

the Master exchange.

53

COMMON MEMORY (CMY) AND LOCAL MEMORY (LMY):

The CP113 has two level memory concepts; the common memory (CMY) incorporates the

common database for all processor and input/output processor. The two common

memories (CMY0 and CMY1) are accessible from all processor and input/output control

(IOC). The CMY is subdivided into four memory banks (MYB) and two memory controls

(MYC). The storage capacity of the CMY is currently 64 Mbytes. The CMY can be

expanded progressively. There may be 16 to 64 numbers of CMYs in CP113.

A separate local memory (LMY) is available to each processor. The LMY contains the

dynamically relevant program and the data, which is only required by there own processor.

SYSTEM PANEL (SYP):

System panel (SYP), in EWSD exchange provides all alarms, both audible and visual, for

all faulty equipments. It also displays the call-processing load of CP in erlongs. Thus, the

system panel provides a permanent over view of the current functional status of the

connected equipment.

Three priority levels can be displayed on the SYPD. These are:

Urgent alarm, e.g. when a unit without standby units fails

None urgent alarm, e.g. when a unit with standby unit fails

Advisories, e.g. when a unit is blocked for testing or repairs

Alarms are displayed in SYPD by LEDs glow and date, time, CP load by three 7-

segment decimal displays. For audible signaling of alarms and advisories, two horns

exist

EXTERNAL MEMORY (EM):

54

The external memory contains two magnetic disc devices (MDD 0 7 MDD 1) and one

magnetic tape device (Mtd0. the MDDs are connected to CP via an interface IOP: MDD in

IIOP and MTD via an interface IOP: MTD in IOP. The MDDs store the following: -

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

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 safe guarded under all circumstances, the

MDD is duplicated. They work as hot standby principle. The capacity of each MDD is 1.2 g.

bytes.

The EM has a magnetic tape device (MTd0 for input and output, purpose, system saving on

magnetic tape is done with the help of MTD. Subscribers call charge tape and detailed

billing tapes are prepared through MTD.

COMMON CHANNEL SIGNALLING SYSTEM NO.7 (CCS-7)

INTRODUCTION

Communication networks generally connect two subscriber terminating equipment

units together via several line sections and switches for message exchange (e.g.

speech, data, text or images). Control information has to be transferred between the

exchanges for call control and for the use of facilities. In analog communication

networks, channel-associated signaling systems have so far been used to carry the

control information. Fault free operation is guaranteed with the channel-associated

signaling systems in analog communication networks, but the systems do not meet

requirements in digital, processor-controlled communication network. Such networks

offer a considerably larger scope of performance as compared with the analog

communication networks due, for instance, to a number of new services and

facilities. The amount and variety of the information to be transferred is accordingly

larger. The information can no longer be economically transported by the

55

conventional channel-associated signaling systems. For this reason, a new, efficient

signaling system is required in digital, processor-controlled communication networks.

The CCITT has therefore specified the common channel signaling system no.7

(CCS-7). CCS-7 is optimized for application in digital networks. It is characterized by

the following main features:

internationally standardized (national variations possible)

Suitable for the national and international intercontinental network level

suitable for various communication services such as telephony, text services,

data services and other services

Suitable for service-specific communication networks and for the integrated

services digital network (ISDN)

High performance and flexibility along with a future-oriented concept which

will meet new requirements

high reliability for message transfer

Processor-friendly structure of the messages (signal units of multiples of 8

bits)

signaling on separate signaling links; the bit rate of the circuits is therefore

exclusively for communication

signaling links always available, even during existing calls

use of the signaling links of transferring user data also

used on various transmission media

o Cable (copper, optical fibre)

o radio relay

o satellite (up to 2 satellite links)

SIGNALLING NETWORK

In contrast to channel-associated signaling, which has been standard practice until

now, in CCS7 the signaling messages are sent via separate signaling links (see Fig.

2.1). One signaling link can convey the signaling messages for many circuits.

56

The CCS7 signaling links connect signaling points (SPs) in a communication

network. The signaling points and the signaling links form an independent signaling

network, which is overlaid over the circuit network.

A distinction is made between signaling points (SP) and signaling transfers points

(STP).

The SPs are the sources (originating points) and the sinks (destination points) of

signaling traffic. In a communication network these are primarily the exchanges.

The STPs switch signaling messages received to another STP or to a SP on the

basis of the destination address. No call processing of the signaling messages

occurs in a STP. A STP can be integrated in a SP (e.g. in an exchange) or can form

a node of its own in the signaling network. One or more levels of STPs are possible

in a signaling network, according to the size of the network.

All SPs in the signaling network are identified by means of a code within the

framework of a corresponding numbering plan can therefore be directly addressed in

a signaling message.

SIGNALING LINKS

A signaling link consists of a signaling data link (two data channels operating

together in opposite directions at the same data rate) and its transfer control

functions. A channel of an existing transmission link (e.g. a PCM30 link) is used as

the signaling data link. Generally, more than one signaling link exists between two

SPs in order to provide redundancy. In the case of failure of a signaling link,

functions of the CCS7 ensure that the signaling traffic is rerouted to fault-free

alternative routes. The routing of the signaling links between two SPs can differ. All

the signaling links between two SPs are combined in a signaling link set.

SIGNALING MODES

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Two different signaling modes can be used in the signaling networks for CCS7.

In the associated mode of signaling, the signaling link is routed together with the

circuit group belonging to the link. In other words, the signaling link is directly

connected to SPs which are also the terminal points of the circuit group (see Fig.

2.2).This mode of signaling is recommended when the capacity of the traffic relation

between the SPs A and B is heavily utilized.

In the quasi-associated mode of signaling, the signaling link and the circuit group run

along different routes, the circuit group connecting the SP A directly with the SP B.

For this mode the signaling for the circuit group is carried out via one or more

defined STPs (see Fig. 2.3). This signaling mode is favourable for traffic relations

with low capacity utilization, as the same signaling link can be used for several

destinations.

SIGNALING ROUTES

The route defined for the signaling between an originating point and a destination

point is called the signaling route. The signaling traffic between two SPs can be

distributed over several different signaling routes. All signaling routes between two

SPs are combined in a signaling route set.

Network structure

The signaling network can be designed in different ways because of the two

signaling modes. It can be constructed either with uniform mode of signaling

(associated or quasi-associated) or with a mixed mode (associated and quasi-

associated).

The worldwide signaling network is divided into two levels that are functionally

independent of each other; an international level with an international network and a

58

national level with many national networks. Each network has its own numbering

plans for the SPs.

PLANNING ASPECTS

Economic, operational and organizational aspects must be considered in the

planning of the signaling network for CCS7. An administration should also have

discussions with the other administrations at an early stage before CCS7 is

introduced in order to make decisions, for example, on the following points.

(a) signaling network

- -mode of signaling

- -selection of the STPs

- -signaling type (en bloc or overlap)

- -assignment of the addresses to SPs

(b) signaling data links e.g. 64 Kbit/s digital or 4.8 Kbit/s analog

(c) safety requirements

- load sharing between signaling links

- diverting the signaling traffic to alternative routes in the event of faults

- error correction

(d) adjacent traffic relations.

STRUCTURE OF CCS7

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The signaling functions in CCS7 are distributed among the following

parts:

- message transfer part (MTP)

- Function-specific user parts (UP).

The MTP represents a user-neutral means of transport for messages between the

users. The term user is applied here for all functional units which use the transport

capability of the MTP.

Each user part encompasses the functions, protocols and coding for the signaling

via CCS7 for a specific user type (e.g. telephone service, data service, ISDN). In this

way, the user parts control the set-up and release of circuit connections, the

processing of facilities as well as administration and maintenance functions for the

circuits.

The functions of the MTP and the UP of CCS7 are divided into 4 levels. Levels 1 to 3

are allotted to the MTP while the UPs form level 4 (see Figure 3.1).

Message Transfer Part

The message transfer part (MTP) is used in CCS7 by all user parts (UPs) as a

transport system for message exchange. Messages to be transferred from one UP

to another are given to the MTP (see Fig. 3.2). The MTP ensures that the messages

reach the addressed UP in the correct order without information loss, duplication or

sequence alteration and without any bit errors.

Functional levels

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Level 1 (signaling data link) defines the physical, electrical and functional

characteristics of a signaling data link and the access units. Level 1 represents the

bearer for a signaling link. In a digital network, 64-kbit/s channels are generally used

as signaling data links. In addition, analog channels (preferably with a bit rate of 4.8

Kbit/s) can also be used via modems as a signaling data link.

Level 2 (signaling link) defines the functions and procedures for a correct

exchange of user messages via a signaling link. The following functions must be

carried out level 2:

- delimitation of the signal units by flags

- elimination of superfluous flags

- error detection using check bits

- error correction by re-transmitting signal units

- error rate monitoring on the signaling data link

- Restoration of fault-free operation, for example, after disruption of the signaling data

link.

Level 3 (signaling network) defines the interworking of the individual signalling

Links. A distinction is made between the two following functional areas:

message handling, i.e. directing the messages to the desired signaling

line, or to the correct UP

- signaling network management, i.e. control of the message traffic, for example,

by means of changeover of signaling links if a fault is detected and change back to

normal operation after the fault is corrected.

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The various functions of level 3 operate with one another, with

functions of other levels and with corresponding functions of other

signaling of other SPs.

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MECHANICAL DESIGN of EWSD

EWSD uses the modular SIVAPAC packaging system for the mechanical design. Its basic

units are:

Modules,

Module frames in shelves

Racks,

Rack rows,

Cables.

All modules and cables are of the plug-in type. Installation test manuals and acceptance

test manuals are provided to aid the operating company in carrying out commissioning and

acceptance testing for the exchange.

MODULES have a standard format and are mounted vertically in the module frame. A

faceplate on the front edge can have front-facing connectors and display and control

elements; the rear edge is fitted with spring-contact strips, which make contact with the

blade connectors in the module frame. The printed circuit boards are constructed as

multilayer boards. Plated-through holes connect the individual layers with each other

and the components to the layers. Modern surface-mounted devices are used where

high packing density, mounting of components on both sides of the circuit board and

optimum heat dissipation are required simultaneously.

MODULE FRAMES combine the modules to form a constructional and wiring unit. A

module frame basically consists of a backplane, assembly rails, side sections and guide

bars for the modules. The backplane forms the rear section of the module frame. It

consists of a multilayer board with blade contact strips present in to make the electrical

contact. Its contact pins are arranged to project beyond the rear edge of the backplane

so that cable connectors can be plugged in & additional wire-wrapped connections

made.

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RACKS accommodate module frames and auxiliary devices. Wide-opening doors allow

unrestricted access to the built-in system components. Simple clamping elements are

used to connect the racks together to form a rack row and also provide electrical

connections. The racks can either stand directly on the floor of the switching room or on

a raised floor.

THE CABLES are of plug-in design: they are manufactured and tested in the required

lengths and delivered to the site fitted with connectors. During installation the cable

connectors only need to be plugged into the module frame backplane. From the

connector the cables are routed either up to a planar cable shelf or down under a raised

floor.

The compact modular structure of EWSD allows operating companies to install exchanges

requiring remarkably little floor space. This advantageous feature of EWSD allows high-

capacity switching systems to be installed in existing buildings and also in smaller,

therefore less expensive, new buildings.

The above mentioned spaces saving benefits allow powerful EWSD exchanges to be

housed in containers. All racks installed in containers are mounted on shock absorbers,

which protect the racks against vibration during transportation.

EWSD installations obtain their supply voltages (48 V or 60 V dc) from central power supply

units. Standard flexible cables and distribution buses carry the operating voltage to current

converters, inverters and frequency generators. Current converters produce the branch

voltage for electronic circuits; the inverters supply power to ac-operated peripherals as and

the frequency generators supply the ringing tones or meter pulses.

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Natural convection removes dissipated heat from the vertically mounted modules in the

module frames. Dissipated heat can be extracted very easily if the racks are set up on a

raised floor. Also in some cases, slide-in ventilator units in the rack and/or air conditioning

help to dissipate the heat. The main distribution frame (MDF) forms the interface between

internal and external lines. The siemens compact mini-distributor meets the requirements of

most operating companies for space-saving technology. It is suitable for all sizes of EWSD

exchange. Its solder less connection technique, mature technical standard and proven

cost-effectiveness make it an ideal accessory for EWSD.

CALL PROCESSING PROGRAMS: by LTG

In the CP, the call processing programs only handle those call processing functions, which

require access to data available only to the CP:

reading and analysis of call and termination data,

digit translation with the following functions:

1. destination routing with possible route processing

2. charge zone determination

path selection in the SN image and sending of setting commands to the switching

network control,

sending of messages to the group processors with the objective of initiating specific

actions and transferring to the group processors the necessary information for further

independent call processing.

The call processing programs in the group processors (GP) deal with most of their call

processing tasks without involving the CP. They are activated by call processing events

from the LTG periphery, messages from the CP, messages from the DLU, messages from

other GPs and messages from the CCNC. Event and message processing activities of the

GP are as follows:

timing supervision,

evaluation of call data and termination data,

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modification of call data and transient termination data,

identification of signals,

sending of messages to the CP, to other GPs, to the CCNC or to a DLU,

seizure and release of channels,

standardization of signaling before informing the CP or another GP,

control of signaling,

pre-analysis of dial digits,

execution of service-feature specific activities (provided no central coordination is

required),

sending of setting commands to the group switch and

recording of charge data.

ADMINISTRATION PROGRAMS: by LTG

The CP administration programs process the administrative MML commands. Activities

required here are as follows:

incorporation of data into the database,

modification of data in the database,

reading and editing data in the database for output,

using appropriate messages to pass information to the peripheral processors (GP,

CCNP) concerning data modification,

control of traffic measurement processes in the CP and

activation of measurements (traffic and statistics) in the periphery.

In addition, the administration programs save charge, statistics and traffic data in the

external memory. These are obtained from the call processing programs in the CP or

supplied by the administration programs of the peripheral processors.

The administration programs of the peripheral processors (GP & CCNP) process the

messages, which the administration programs of the CP send them. In response they:

inform other peripheral processors in the DLU or the CCNC,

modify their own data (partial image of the database),

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start or end measurements (statistics),

transfer data to the CP.

Where data which are an image of parts of the database are present in other peripheral

processors (such as in the subscriber line modules of the DLU) there are administration

programs in these processors as well which keep the data consistent.

MAINTENANCE PROGRAMS:

The CP maintenance programs process the MML commands that are essential to the

provision of trouble-free service. Activities required here could be as follows:

control of configuration and recovery processes with the aid of safeguarding programs,

control of measurement and testing processes for the subscriber line and trunk network,

control of fault analysis and diagnostic processes,

instigation of configuration, recovery, testing, measurement and diagnostic activities in

peripheral processors using the appropriate messages.

In addition, they process messages containing measurement, testing and diagnostic results

from the LTGs (GP). Another function of the maintenance programs is to display faults on

the system panel and provide audible signals foe them where necessary.

The maintenance programs of the GP process:

messages from maintenance programs in the CP,

results from the test units in the DLU and test equipment for trunks in the LTGs and

messages from supervision equipment and supervision programs in the LTGs (e.g.

trunk maintenance).

Possible GP reactions are as follows:

sending control messages to test equipment,

starting test and diagnostic procedures,

executing configuration measures and

sending messages to the CP or the DLUs.

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TYPE OF INTERFACES

1). PDC ( primary digital carrier): it is between dlu and ltg.

2).SDC ( secondary digital carrier ): it is between ltg and switching network .

CALL SETUP

The simplest way to give an overview of the interoperation of the functional units and the

functions of the associated controls is to describe an internal connection, i.e. a connection

between two subscribers served by the same exchange.

In the following text, the functional units assigned to the calling subscriber (or A-subscriber)

are designated A-… (E.g. A-DLU, A-LTG) and similarly for subscriber B. a connection thro’

the exchange is always made up of separate connection paths for each direction of

transmission (A to B, B to A).

The description of an external call setup between two analog pushbutton subscribers is

followed by some comments on call setup in the integrated services digital network (ISDN).

In both cases the subscribers are connected to the exchange via two-wire lines.

OUTGOING CALL SET-UP (Originating Traffic)

State (a): If a channel is idle and ready to be seized, the call-processing state CHANNEL

IDLE is shown in the channel register (A-CHR) allocated to this channel in the CP.

(1) The calling subscriber (A-SUB) lifts the handset of his telephone (goes OFF

HOOK), thereby seizing call-processing equipment and initiating a call setup.

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(2) The processor in the SLMA (A-SLMCP) in the DLU continuously scans the

analog subscriber line circuits (A-SLCA). It detects a seizure by an A- subscriber

and informs the control for digital line unit (A-DLUC) about the seizure. This A-

DLUC is responsible for the setup and final clearing of the call.

(3) Via the digital interface unit in the DLU (A-DIUD) and the digital interface unit in

the LTG (A-DIU), the A-DLUC sends the SEIZURE AD message to the group

processor (A-GP). A call register (CREG) is made available to the A-OP for

buffering call-specific data.

(4) The A-GP determines the category of the A-subscriber, in this case an ordinary

subscriber with DTMF dialing, and verifies this subscriber’s authorization for

telephoning, allocates a time slot (channel) to the subscriber, and informs the A-

DLUC.

(5) The A-OP sends the SEIZURE A message to the CP via the semipermanently

switched message channel, which serves for the exchange of information

between the A-OP and the coordination processor (CP) and leads through the

switching network (SN).As a result of the call-processing state CHANNEL IDLE

and the arriving event SEIZURE AD, a procedure of the call-processing

programs is called in the CP.

(6) The CP seizes port A and the user channel that is allocated to the calling

subscriber.

State (b): The seizure creates the new state PORT A SEIZED, which is written into the

channel register (A-CHR) replacing the old state. In accordance with the state/event table

the new state causes the next procedure to be called.

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(7) The A-DLUC sends the time slot specified by A-GP to the A-SLMCP via the

control network. The A-SLMCP causes the time slot to be loaded into the

COSLAC (Customer optimized subscriber line audio processing circuit) in

ASLCA.

(8) The A-GP sets up the group switch (A-GS) and initiates a test of the connection

paths, starting from the signaling unit (SU) the A-LTG via the A-GS to the digital

interface unit (A-DIU), and from there via the 4096-kbit!s network in the allocated

time slot to the A-DIUD in the digital subscriber line unit (DLU), then on to the A-

SLCA of the A-subscriber and back again to the A-LTG. For this test the tone

generator (TOG) in the signaling unit (SU) sends out a test tone to be received

by a code receiver (CR).

(9) When the test has been successfully completed, the A-OP sends a command to

the A-SLMCP to through connect the connection paths for the dial tone and for

the digits dialed by the A-subscriber.

(10) The tone generator (TOG) in the signaling unit (SU) of the A-LTG connects the

dial tone.

(11) Having received the set up command, the A-SLMCP checks the subscriber loop.

If this test is positive, the SLMCP through-connects the dial tone to the

subscriber.

(12) Reception of the dial tone by the A-subscriber is the request to start dialing.

(13) An interval timer (IT) monitors the dial tone transmission in order to ensure that

switching equipment will not be seized for an unnecessarily long time. The A-

subscriber should start dialing within a predefined period of time (say, 10

70

seconds) after reception of the dial tone, otherwise the switching equipment is

cleared again by the timer. In the latter case, busy tone is sent to the subscriber

instead of the dial tone.

(14) The A-subscriber starts dialing. The digit is sent to the code receiver (CR) in the-

A-LTG via the subscriber line circuit (A-SLCA), via the allocated time slot in the

4096-kbit/s network, the A-DIIJD and a PDC channel.

(15) The CR receives the digits and forwards them in digitized form to the A-GP,

where they are buffered in the call register (A-CR..EG).

(16) As soon as the A-SLMCP detects the input of the first digit by the A- subscriber, it

disconnects the dial tone.

(17) Then the dial tone is switched off by the A-GP.

(18) Meanwhile the A-subscriber has dialed further digits, which are stored by the A-

GP in the call register until a defined number of digits for digit translation in the

CP, have been received.

(19) When the digit-block analysis in the A-GP has supplied a sufficient number of

digits, all digits are transferred to the CP with the DIGITAL BLOCK message.

(20) The CF has a call-processing buffer (CPB), which is connected to the channel

register (A-CHR). The CP stores the digit block in the CPB.

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(21) Since the number of digits varies according to the requested destination, the CP

in each case determines the number of digits to be expected, and compares the

result with the digits received.

If the number of digits is sufficient, and when translation of the same has been completed,

the CPB is no longer needed and is released.

If the number of digits is incomplete, the CP sends the COME AGAIN command- to the A-

GP. With this command the CP indicates the number of missing digits that are required for

the through-connection. Iii this case, too, the call-processing buffer, a working CPB, is

released. For the buffering of the next digit block another CPB is requested.

State (C): - The old state (b) PORT A SEIZED in the channel register (A-CHR) is canceled

and the new state (c) PORT A RECEIVING is entered.

(22) In the meantime the A-subscriber has dialed further digits, which have been

received by the A-GP and buffered in the call register (CREG).

(23) The A-GP sends the DIGIT BLOCK message to the UP again. The CE stores the

digit block in the CPB. After translation of the digits received the CP recognizes

the desired destination.

(24) With the aid of its memory, the CP ascertains whether a route to the desired

destination exchange (B-EX) is idle. It also determines the zone for call charge

registration, and performs path selection. If all direct routes to the B-exchange

are busy, the CP performs alternate routing, i.e. the connection is set up via a-

transit exchange

(25) If the result is positive, i.e., if a route is idle, the CP seizes the appropriate B- port

and the route.

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(26) The CP sends the SET UP SN command to both switch group controls (SGCs).

As a result, the connection paths (selected in the CP) between the A-LTG and

the B-LTG are through-connected via the two switching network units SN0 and

SN1.

(27) The CP sends the SEIZURE BT command, together with port-B data and the

digits, to the B-GP.

(28) The 13-OP has a call-register (CREG) at its disposal, into which it enters the port

B data and the digits.

(29) With the SETUP command the CP sends the zone index to the A-OP.

State (e): In the A-CHR, the old state. PORT A- RECEIVING is canceled and the

new state PORT A TO PORT B is entered.

(30) The A-GP receives the zone index and stores it in the CREG and starts-the -

cross-office check (COC In the COC, the quality of the transmission paths for-the

user information between A-LTG and B-LTG is checked.

The cross-office check begins with an instruction to the EJU (link interface unit between

LTG and SN)

A test pattern generator (TPAG) in the LII) of A-LTG sends several bit patterns (test

patterns) to, the LIU of B-LTG via the set up connection paths of the two switching network

units.

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In the LIU of the 8-LTG, the bit patterns are looped back and returned to the LIU of the A-

LTO via the switching network, A test pattern evaluation circuit (TPAEC) in the A-LTG

compares the transmitted bit patterns with the received bit patterns. If they do not match,

the TPAEC sends an error message to the A-GP.

(31) The A-OP evaluates the cross-office check. Tithe result is positive, it sends a set

up command to the group switch (OS), through-connecting the Connection paths

between the digital interface unit (DLU) and the link interface unit between LTG

and SN (LIU).

(32) The A-OP sends the SETUP COMPLETE report plus further digits directly to the

B-GP.

(33) The B-OP stores the digits in the call register (CREG).

(34) The B-OP disconnects the loop-around” for the COC and seizes the trunk

selected by the CP.

(35) Over the outgoing trunk, the B-OP sends digits from the CR130 to the distant

exchange (B-EX).

(36) In the meantime, the A-GP has received and structured in the A-CREG further

digits dialed by the A-subscriber.

(37) With the DIGIT TRANSFER report, the A-OP sends the stored digits to the 8-

GP.

(38) The B-OP stores the received digits in the call register (B-CREG) again.

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(39) The B-OP sends the digits to the distant exchange (8-EX) over the trunk.

(40) As soon as a sufficient number of digits has arrived at the distant exchange, the

backward signal ADDRESS COMPLETE is transmitted by (hat exchange (only if

the appropriate signaling system is used).

(41) The B-GP sends the ADDRESS COMPLETE report to the A-GP.

(42) The B-OP sets up the group twitch (OS).

This completes the call setup in the originating exchange.

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76

CONNECTIONS IN ISDN

The EWSD exchange can switch connections for various services in ISDN (e.g. for

Telephony, Telefax, Teletex, data transmission). To do this it requires specific information

identifying each service. Accordingly the messages to be exchanged for a call set up

always contain supplementary information identifying the service involved.

To set up an ISDN connection, LTGs and CP largely perform the same functions as for a

connection between analog subscribers. Messages are exchanged between the LTGs and

between the LTGs and between the CPs via same message paths.

The main difference to the setup of a connection between analog subscribers lies in the line

periphery. Basic access as per CCITT contains two B channels of 64 kbps and a D channel

of 16 kbps. The SLCD divides the bit stream coming from the subscriber into two 64 kbps

streams and one 16 kbps stream and passes these on accordingly. In the opposite

direction it unites the two B channels and the D channel into one bit stream. The SLMD

handles the B- and D-channel information for several SLCDs; it separates the D-channel

information into signaling information and e.g. packet mode data and passes them on

accordingly; in the other direction it combines them and sends them to the subscriber.

Several terminals for different services can be connected to a passive bus for basic access

at the subscriber’s premises.

ISDN terminals and the DLU exchange digital information over the 2 B channels and the D

channel of the subscriber line in full duplex mode. An echo compensation procedure

separates the two transmission directions from one another (layer 1 of ISO reference

model).

The two B channels of a basic access are of equal value. They are independent of one

another and can transmit voice and text as well as still images and circuit switched and

packet switched data in bit-transparent mode.

The D channel is operated in packet-oriented mode for signaling to and from the subscriber

as well as for data with low bit rates (packet mode data including telemetry data). A

transmission protocol (LAPD=link access procedure for D channel, layer 2 of ISO reference

model) safeguards the transmission of the D-channel information and facilitates parallel

77

signaling and data transmission for several services between the SLMD and the terminals.

To this end each transmission block of the D channel contains two octets in its address

field of which the first (SAPI=service access point identifier) identifies the information type

and the 2nd, the TEI (terminal endpoint identifier) identifies the terminal at the ISDN

subscriber’s premises. LAPD uses the HDLC transmission protocol (HDLC=high-level data

link control).

Signaling for call set up and feature control between terminal and LTG uses standard

messages (D-channel protocol between terminals and DLU, a subset of CCS7 between

DLU and LTG, layer 3 of ISO reference model).

To set up a connection, terminal and LTG exchange messages via the D channel, SLMD,

DLUC and DIUD. Information can also be transmitted to and from the subscriber during the

connection. Normally only one of the 2 B channels is used for a connection; the other is

simultaneously available for a 2nd connection of any type.

OPERATION AND MAINTENANCE

The following table lists the functions belonging to O&M, which are organized in

accordance with CCITT recommendations. Functions integrated into the system guide and

support the operators in the O&M of EWSD exchanges. They reduce the activities that

need to be carried out manually by the personnel. The man-machine language (MML)

implemented in EWSD and standardized by CCITT is easy to learn and rationalizes the

work of the operating personnel at O&M terminals (OMT). MML is also used to

communicate with the system for installation, acceptance test and extension purposes.

OPERATING MODES

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The operating company can choose to have O&M functions performed only locally in the

exchange or additionally in an O&M center (OMC). Both modes can be used in the same

telecommunication network, and if necessary it is easy to convert from one mode to

another. The decision governing which mode is used for an exchange is largely dependent

on factors such as the local network environment, the wishes of the operating company and

the number and the size of EWSD exchanges installed in the network.

LOCAL O&M:

This mode is recommended if an EWSD exchange is installed as the first digital exchange

in an existing conventional telephone network (digital island). O&M tasks are carried out in

the exchange itself using a basic selection of equipment, comprising a system panel (SYP),

one duplicated operation and maintenance terminal (OMT) and a magnetic tape device

(MTD). Other equipment can be easily added if required. The following can be used as an

OMT: printer terminal (PT) or video display unit (VDU) with printer or personal computer

(PC). The software for local O&M is located in the CP.

OPERATION MAINTENANCE

Subscriber administration:

Directory numbers data

Subscriber terminals and data

Call charge data

Charge observation

Malicious call tracing

Routing administration:

Trunk and trunk group data

Routing data

Maintenance of subscriber lines:

Testing

Measuring

Maintenance of inter-exchange trunks:

Testing

Measuring

Hardware maintenance:

Alarm reporting

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Traffic administration:

Measurement

Supervision

Observation

Tariff and charging administration:

Tariffs and zones

Accounting statistics

System control operation:

Input authorization

Output management

File administration

Device assignment

Job administration

Calendar administration

O&M network administration

Network management administration:

Network management control

Network management data

Services administration:

Operator service system data

Centrex data

Special networks administration:

Mobile network data

Free phone network data

Fault clearance

Special fault clearance

Servicing

Software maintenance:

Modification of exchange

software

Modification of O&M software

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CENTRALIZED O&M:

EWSD exchanges allocated to an OMC are operated and maintained jointly. This allows

O&M tasks to be concentrated at specific OMTs where they can be handled by specialized

personnel. In centralized O&M, the exchanges themselves are unattended. Centralized

O&M is cost-effective even for only a small number of exchanges. The small group

terminals in the OMC have access to all exchanges. The exchanges retain the O&M

software and the basic selection of equipment for local O&M. This allows the O&M

personnel to carry out all operation and maintenance tasks such as local fault clearance in

the exchange, even though O&M is normally centralized.

The following devices are connected in the OMC:

Operation and maintenance terminals (OMT, either VDU or PC) for interactive functions,

Magnetic tape devices (MTD) for the input and output of bulk data,

Magnetic disk devices (MDD) for back up storage of programs and data and as mass

data storage and

System panel(s) for the display of alarms and advisories from the exchanges.

An OMC contains either a centralized system panel (CSYP) for several exchanges or one

system panel (SYP) for each exchange. The OMT, MTD and MDD are connected to a data

communication processor (DCP).

The DCP collects and distributes information on the one hand to and from the exchanges

(over dedicated lines to the coordination processors) and on the other hand to and from the

devices connected in the OMC. It collects data, stores it externally and controls MML dialog

and file transfer.

It is a very simple matter to expand the O&M equipment (for example to increase the

number of O&M terminals).

The OMTs can be arranged according to the organizational requirements of the operating

company. Task-related groups of OMTs can be set up in the desired locations (e.g. within

the OMC or remotely from it). The range of tasks can be freely defined; terminals can be

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assigned to any task and assignments can be changed as required by means of MML

commands.

O&M NETWORK

Hierarchical or intermeshed O&M networks can be created by linking separate OMCs (i.e.

by networking the DCPs). In an O&M network, one OMC can access all other OMCs and

thus all exchanges with centralized O&M. For night concentration one OMC can

automatically take over the O&M functions of other OMCs, i.e. at a predetermined time of

the day.

It is most efficient to post-process data collected at the exchanges (e.g. call charge data)

on commercial data processing systems. The O&M network is used to transfer

accumulated data between the OMCs, a data processing system and, if appropriate, other

data bases (file transfer). This allows data to be processed rationally and safely, particularly

in case of large volumes of data such as those that accumulate during charge registration

or large-scale cutover of subscribers. Pre- and post-processing programs (administration

support systems ADSS) are available for a number of tasks.

DIALOG MODES

The convenient man-machine language (MML) as per CCITT is a major contributing factor

to fast, error free dialog. It is easy to learn and to understand; all inputs are acknowledged.

The operator thus receives information on the results of all the inputs. The commands are

based on mnemonics derived from common telecommunications terms and adapted to

different national languages. Most outputs do not contain abbreviations and are self-

explanatory.

The operator starts a man-machine dialog by entering an access authorization – either by

entering a password or turning a key switch. The access authorization defines a range of

commands that can be used by that operator at that OMT and thus prevents misuse.

The EWSD MML offers the operator a choice of dialog types: direct mode, prompting mode

and menu mode. Direct mode means that the operator enters a command with all of its

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parameter names and values at once. This is a very fast method of working, suitable for

experienced operators. Less-experienced operators can use the prompting mode, where

the system guides the operator and asks for each parameter individually until the command

is complete. Menu mode guides the operator thro’ a menu tree from a general menu to the

required task and thus the required command. For instance, an operator may select the

task “subscriber administration” out of the general menu “administration functions

exchange” and the appropriate on-screen form will be displayed. This form leads thro’ the

form “subscriber standard functions” to the form “create subscriber”. The operator enters

the necessary parameter values in the fields of the form and sends it off as a command. An

operator can also select the desired form directly by entering its identification code.

When necessary, the operator can call up help texts which contain explanations or

additional instructions for filling out the form. Operating convenience is enhanced by

numerous dialog control functions such as paging thro’ help texts or temporary storage of

forms.

There are two versions of MML corresponding to the dialog types:

Basic MML (BMML), which is designed for operation at command level, and

Extended MML (EMML), which has a more extensive user interface. It is based on

menus and forms.

Typical Actions of a BMML Command

Action Meaning

CR Creation (setup). Creates the given object in the database of the

system.

e.g. CR ROUTE creates a route.

CR LTG creates a line trunk group.

CAN Cancel (delete). Deletes an object in the system which was usually

created with “CR”.

e.g. CAN ROUTE deletes a route.

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CAN LTG deletes a line trunk group.

CONF Configuration. Change the operating status of an object in the

system which was usually created with “CR”. e.g. CONF LTG

changes the operating status of a line trunk group.

STAT Status display. Protocols the operating status of e.g. HW units or

call processing units.

e.g. CON LTG displays the operating status of an LTG.

DIAG Diagnosis. Diagnoses the unit specified under “object”.

e.g. DIAG LTG diagnoses the LTG.

MOD Modify. Changes the data of an object in the system which was

usually created with “CR”.

e.g. MOD ROUTE modifies the data of a route.

DISP Display (protocol). Protocols data stored in the system which was

usually created with “CR”.

e.g. DISP ROUTE displays the route data.

CASE STUDIES IN MDF

In exchange the testing of a subscriber telephone line is checked in MDF. They test the

resistance, capacitance & voltage on the line and made over the fault to the concerned

lineman. As I have learnt testing in MDF under the supervision of BSNL employee.

A subscriber has complaint against a number 0183-2270515 (Telephone

dead).

Solution: The telephone number in the MDF is tested using PCLMB software provided by

NOKIA SEIMENS Pvt. Ltd to BSNL. This software is a user friendly and easy to use.

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There are three possible cases:

Case 1: Break in subscriber’s line

In the group test, Capacitance of the subscriber line comes out to be zero. It means there is

break in subscriber’s line. In ideal case the capacitance of the line is 1.0 µF.

Case 2: Earth on the subscriber’s line.

Output of the above action is given as:

A/B A/E B/E

DC -1.2V -1.4V -0.1V

AC 0.1V 0.1V 0.1V

R 10.00MΩ 10.00MΩ 7.4MΩ

C 0.0µF

A/B A/E B/E

DC -1.2V -1.4V -0.1V

AC 0.1V 0.1V 0.1V

R 10.00KΩ 10.00KΩ 7.4KΩ

C 1.2µF

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In the group test, resistance of the subscriber line comes out to be 10.0Kilo-ohm. But in

ideal case its value should be in MΩ.

Case 3: External potential (AC / DC voltage) on subscriber’s line.

In the group test, External potential on the subscriber line comes out to 50 Volts. In ideal

case there should be no AC/DC Voltage on the subscriber’s line.

The lineman is informed about the fault on the line to take the action accordingly.

CASE STUDIES IN SWITCH ROOM

The main work in the switching room is only to install the modules that are discussed

before. First is to install the racks in the room and then to install the modules in these racks

and then connect them with the MDF room through the transmission room. After the

installation of the switch room, there is the work to operate them by the software and

maintain them through the OMC room and other fault occurs in the cards that are replaced

when there is fault in them and send for the repairing. The fault occurs due to any fault in

the electronic equipment install in that card.

A/B A/E B/E

DC -1.2V -1.4V -0.1V

AC 50V 50V 40V

R 10.00MΩ 10.00MΩ 7.4MΩ

C 1.2µF

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Case 4: No Dial Tone

If there is No Dial Tone on DP pair of the concern subscriber, then lineman informs the

MDF people about no dial tone case. MDF people confirm No Dial Tone; the fault is made

over to Switch room.

First of all check the status of the subscriber using following BMML command.

STATSUB: LAC=0183, DN=2702086;

Output:

LAC DN CAT EQN STATUS

--------------I-----------------I------------I---------------I--------------------

0183 2702086 MS 30-2-1-6 DIDLE &

BPRM

DLUY0

Here:

LAC : LOCAL AREA CODE

DN : DIRECTORY NUMBER

CAT : CATEGORY

EQN : EQUIPMENT NUMBER

STATUS : STATUS OF THE NUMBER

BPRM : BLOCK PERMANENT

Now Test the Port / EQPT Number Which is allotted to the above subscriber. The BMML

command is given as,

TEST DLU LC: DLU=30, LC=2-1-6;

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Output:

TIME TESTED BUSY FAULTY NACC

------------I---------------I-------------I--------------I-------------

11:37 1 0 Ringing 0

Here:

NACC : Not accessed

LC : Line circuit

FAULTY : Ringing, here it means there is some problem in the card.

For this fault the concerned card has to be replaced in the DLU.

Replacement of the card is done in two steps:

Step1: We have to deactivate all the 16 subscriber circuits present on the card.

The BMML command for the step1 is as:

CONFDLUMOD: DLU=30, MOD=2-1, OST=MBL;

Output:

It will configure the DLU NUMBER=30 having Module 2-1 and change the state Active to

Blocked.

Here:

MOD : Module

MBL : Maintenance Blocked

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OST : Operating State

Now replace that faulty card manually.

Step2: We have to activate all the 16 subscriber circuits present on the card.

The BMML command for step2 is as:

CONFDLUMOD: DLU=30, MOD=2-1, OST=ACT;

Output:

It will configure the DLU NUMBER=30 having Module 2-1 and change the state Blocked to

Active.

Case 5: DLUEQ Card Faulty

The command DISP ALARM is executed daily as it is a routine testing command. The

output of DISP ALARM gives us alarm if any. In case of any fault alarm is displayed.

From alarm we get to know that DLU=20 is faulty and this DLU needs to be diagnosed.

The MML Command for checking the status of the DLU is given as:

STATDLUEQ: DLU=20, DCC=X-X; EQ=Equipment

Output:

DLU DCC OST

----------I--------------I-----------

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20 0-0 ACT

20 0-2 ACT

20 1-0 ACT

20 1-1 ACT

20 1-2 DST

20 1-3 ACT

20 2-0 ACT

20 2-1 ACT

20 2-2 ACT

20 2-3 ACT

20 3-0 ACT

20 3-1 ACT

20 3-2 ACT

20 3-3 ACT

The CONF command is used to change the Operating status from ACT to MBL

(Maintenance Block) is given as:

CONFDLUEQ: DLU=20, DCC=1-2, OST=MBL;

Output:

DLU DCC OST

----------I----------------I------------

20 1-2 MBL

Now diagnose the particular control card by giving the BMML command as:

DIAGDLUEQ: DLU=20, DCC=1-2;

Output:

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Hardware fault detected.

Now replace that faulty card and again diagnose the card.

DIAGDLUEQ: DLU=20, DCC=1-2;

Output:

No fault detected.

Now give command to activate the card as,

CONFDLUEQ: DLU=20, DCC=1-2, OST=ACT;

Output:

DLU DCC OST

----------I----------------I------------

20 1-2 ACT

Now, again if you want to check the status the give following command,

STATDLUEQ: DLU=20, DCC=X-X; EQ=Equipment

Output:

DLU DCC OST

----------I--------------I-----------

20 0-0 ACT

20 0-2 ACT

20 1-0 ACT

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20 1-1 ACT

20 1-2 ACT

20 1-3 ACT

20 2-0 ACT

20 2-1 ACT

20 2-2 ACT

20 2-3 ACT

20 3-0 ACT

20 3-1 ACT

20 3-2 ACT

20 3-3 ACT

SYSTEM STATUS DISPLAY:

The status of the exchanges linked to the OMC is displayed on a video display unit. The

system status display indicates faults in the exchange to the operating personnel in the

OMC. For this purpose the screen displays are organized on three levels (zoom effect).

The first level gives a general picture of the status of all exchanges operated from the

OMC. If for example an alarm has occurred in any one of these exchanges, the operator

can ask for the next display to select the exchange in which the fault is located. In the 3 rd

level display the faulty subsystem can be localized.

Alarm reports are stored on magnetic disk in the CP and can be used for the location of

faults.

SYSTEM PANEL:

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The system panel (SYP) displays not only the alarms and operational statuses of the

exchange but also alarms in the exchange environment, e.g. fire, the status of power

supply and air-conditioning plant and the entry of non-authorized personnel into the building

or container.

Each EWSD exchange is assigned a local SYP and in case of centralized O&M additionally

a SYP in the OMC. There it may be of advantage to combine the SYPs assigned to

different exchanges to form one central SYP in the OMC. A SYP integrated in the monitor

panel of the CSYP can be switched to display the data on any selected exchange. The

alarm paths to the indicators on SYP and CSYP are physically separate from the alarm

paths to the system status display. This ensures a very high level of security in alarm

reporting.

MAINTENANCE FUNCTIONS

TESTS AND MEASUREMENTS:

In EWSD, functions for tests and measurements on subscriber lines (i.e. telephone set,

line, circuit) and trunks are integrated in the system. The operator enters test jobs at the

OMT and the results are output to the OMT or a printer. An OMT can be assigned as a

special test position (task-related OMT); the operator can enter calls for testing and has

facilities for audible and verbal monitoring.

For fault clearance or first-time installation the functions of a telephone set can be tested

from the subscriber’s premises without involving other personnel. An automatic integrated

service feature called ring back service (RBS) is available for this purpose.

HARDWARE MAINTAINENCE:

Preventive maintenance is not required in EWSD because of the automatic in-service

supervision. Maintenance is restricted to measurement checks and fault clearance.

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When an error message occurs an operator in the OMC locates the faulty equipment, if

necessary, by following the corresponding procedures in the maintenance manual.

Immediate corrective action is not necessary because the EWSD architecture and its

safeguarding measures (redundant structures, duplication of vital parts of the system,

automatic changeover to standby etc.) limit the effects of faults and prevent them from

penetrating beyond their immediate vicinity. A technician is sent to the unattended

exchange and changes the affected module.

SOFTWARE MAINTENANCE:

In EWSD a set of powerful support software tools are available for necessary software

corrections and extensions.

Software Corrections

In-service supervision uses self-checks, endless loop detection and other methods to

detect any irregularities in the software which can effect normal operation of EWSD.

These effects are limited by various means. After a deviation or irregularity has been

detected, the operators are given all the necessary information (e.g. diagnostic reports,

error statistics) to enable a correction to be made. The software development center

defines the correction and documents it; apart from this rapid corrections at machine-

language level are also possible.

Software Extensions

These include either charging the exchange (e.g. connecting extra trunk groups,

“quantitative extensions”) or incorporation of additional features (e.g. CCITT common

channel signaling system no. 7, “qualitative extension”). Besides implementing new

software subsystems, this can involve an extension of the database: quantitative

extensions increase the size of the database; qualitative extensions affect its structure

to some extent. Software support is used to expand or alter the database in such cases.

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SOFTWARE QUALITY ASSURANCE:

The use of the CCITT high-level languages CHILL and SDL during the development and

testing is a significant factor in the excellent quality assurance in the extensive EWSD

software. The use of the CHILL makes the all aspects of producing software much easier

and the much faster. The administrative separation of the development and test department

s insure that software is evaluated objectively.

The software development is governed by the precisely defined software engineered

production plan. The inspections are undertaken after the each of the predefined

development stages.

DESIGN VERIFICATION:

For each software product, specialist perform the precise check on whether the failed

feature specifications have been adhered to all the interfaces are then coded in chill,

compiled and stored by the compiler in the project library. This contains the all the available

parameters, procedures, and other interfaces device. The inertly consistent project library

constitutes important prerequisites for creation for errors free APS.

CHECKING OF THE CODED MODULE:

Software modules undergo a code review and the off line test. In the code review

specialists checks whether the code is correct and whether it adheres to the programming

conventions. Where the necessary they identify the malfunction with the real time

conditions and suggests the possible reduction of the requirement and runtimes.

The code review is followed by the off line test of the modules on the commercial data

processing system and a bit by bit comparison with the interfaces stored in the relevant

project library. This completes the development and the testing of the individual software

modules.

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SYSTEM TESTING:

The system test is undertaken by the department independent of the developers and run on

the switching processors. The system test shows how the complete software behaves in

the system. The system remains in the behavior must remain stable under load and the

react in the controlled manner when the hardware faults are simulated.

In the automated regression test, the programs simulate operating devices process

command files and check system.

PROBLEM FORMULATION

Work in the training: there is the followings part of the exchange where the work was

undergoing when the exchanged was installed:

Main distribution frame

Power plant

Switching room

Transmission room

OMC room

The all work in these parts of the exchange is explained below:

MAIN DISTRIBUTION FRAME:

In the main distribution frame, there are two sides:

1. Exchange side (equipment side)

2. Line side ( vertical side)

The work in this part is jump-ring that is done with the wire that is called the jumper wire. It

is nothing but the connection of the telephone lines from the exchange side to the

subscriber side in this the number is given to an subscriber through the cable. From this,

we can find out whether the fault is in the exchange or in the field side. There is the use of

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the GD tube that is used as the fuse between the exchange and the field. If there is the

lightening in the field or any touch of the phone line with the high power voltage line then

there may be damage in the exchange, so when such case occurs the GD fuse gets burns

that can save the exchange from the damage. GD stands for the ground discharge tube.

POWER PLANT:

The power plant gives the supply to the whole exchange so there equipment such as the

transformer there is work to learn how this work there is also a set of the invertors. There

may be failure of the power supply due to the any fault in the SMPS. Main problem occurs

due to the power supply failure in the exchange then the battery gets the automatically

starts but these battery can give the power supply only the 5-6 hours then voltage goes on

decreasing. The voltage should remain the –48v if it is not then the exchange will stop

working so when such happens the generators get started.

POWER PLANT IN EXCHANGE

INTRODUCTION

The POWER PLANT of any telecommunication system is usually referred as the “Heart” of

installation since the communication system can function only as long as power supply is

available.

The importance of power plant for any system need not be stressed.

Therefore, utmost care has to be taken for their proper handling to ensure uninterrupted

and fault free working of power plant.

POWER PLANT REQUIREMENT

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The requirement of power plant for main exchange and are different because of the types

of equipments. In main exchange equipment there is very little variation in peak hour and

slack hour load of power plant contrary to electromechanical exchange where the load

varies with traffic. Therefore, power plants are designed for continuous handling of constant

load-both at RLU and main exchange.

Any Power Plant for communication should have two basic characteristics:

a) Reliability of components of Power Plant and continuity of power supply.

b) The power fed the exchange equipments should be free from hum, noises.

ARRANGEMENT AT MAIN EXCHANGE

The main exchange requires two types of supplies. The first one is –48 v dc supply mainly

for switch room and second one is 220 v ac supply for OMC room, exploitation room and

switch room mainly for computer peripheral devices. The –48 v dc supply requirement is

met by a power plant similar to all other types of exchanges. This has essentially rectifiers

on load sharing basis, two battery sets and a switching cubicle. The operation and

maintenance features are same as in other types of exchanges.

The requirement of 220 v ac power supply is met through direct main supply and invertors

which converts –48 v dc supplies into 220 v ac supply. The –48 v dc power is taken from

rectifiers and fed to invertors. The invertors convert the dc supply into 220 v ac supply. The

reasons for using invertors are, firstly uninterrupted power supply due to battery available

as standby and secondly availability of stabilized power supply, free from variations in

voltage and frequency. This ensures safety of both the equipment and the programs stored

in various storage devices.

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PROVISION OF STAND BY POWER SUPPLY

The power plant essentially consist of two units:

1. Float Rectifiers

2. Batteries

FLOAT RECTIFIER:

It converts A.C. voltage into D.C. voltage (+48V). There may be several Float Rectifiers in

the exchange depending upon requirement of load.

The rectifying element consists of silicon diodes of appropriate voltage & current ratings so

as to suit the charging current required for charging of batteries under different conditions.

The battery charger can also be used as a float charger in the event of failure of float

rectifier

by utilizing the filter element associated with later. Under these circumstances, o/p voltage

can be adjusted between 50 and 52 volts under varying conditions of main voltage and

load.

The float rectifier has fully automatic stabilization of voltage (51.5 +- 0.5 volts.).

BATTERIES:

There may and must be two or three set of batteries in an exchange. Each set contains 24

cells, each having voltage to be 2v which turns to be approximately 2.5 amperes in the form

of current. Both of the cells trace voltage of 48v by getting combined as illustrated below:-

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Voltage of one cell (24v)+ voltage of other cell (24v)=

48v (total voltage)

if the main supply is cut-off then we use these batteries for some time until their charge

gets finished. Batteries are connected in parallel to the power supply so that if main supply

is functioning then batteries are cut-off otherwise batteries will handle the entire load of the

exchange just after the failure of main power supply.

Batteries are also called to be the secondary voltage sours.

BATTERY CHARGER:

It charges the batteries automatically when the voltage of batteries goes down to a certain

level with the passage of time or due to their extensive and long use. It keeps on charging

the batteries until they are fully charged.

Both MAIN EXCHANGE and RLU exchanges in many parts of the country are subjected to

prolonged power cuts. Therefore, battery capacity is not at all sufficient for maintaining

uninterrupted supply to various units in the exchange. Also to maintain proper

environmental conditions inside main exchang air

conditioning plants have to be run continuously for which continuous mains power supply is

required. Therefore, to take care of all possibilities and ensure continuous supply engine-

alternator must be provided at both the places i.e. Main exchange and RLU exchange.

Preferably a standby engine alternator should also be provided. Sufficient quantities of

diesel oil should also be kept into stock taking into account the supply of oil is erratic,

minimum 72 hours storage should be maintained.

The capacity of engine alternator provided at main exchange and RLU depends on their

load requirements of the equipment and a/c plant. At RLU, the load is comparatively very

small due to very few types of equipment and only window type ac units are required there.

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CONCLUSION

The power plant is a very vital organ of main and RLU exchanges. The main exchange

power plant requires all the units of regular power plant used in other exchanges for –48 dc

supply and in addition it requires 220 v ac supplies for OMC and peripheral devices. The

provision of engine alternator is a must at main and RLU exchanges and it should be

capable of taking combined load of exchange equipments and a/c plant.

SWITCHING ROOM:

The main work in the switching room is only to install the modules that are discussed

before. First is to install the racks in the room and then to install the modules in these racks

and then connect them with the MDF room through the transmission room. After the

installation of the switch room, there is the work to operate them by the software and

maintain them through the OMC room and other fault occurs in the cards that are replaced

when there is fault in them and send for the repairing. The fault occurs due to any fault in

the electronic equipment install in that card.

PROCEDURE FOR HANDLING SUBSCRIBER COMPLAINTS

Some common complaints are as follows:

TELEPHONE DEAD

Case 1 Problem concerned a particular subscriber

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a) Perform both exchange side tests and outside plant open loop test on the terminal

b) If the outside plant open loop tests fail, the fault lies in the outside plant. Most likely

there will be disconnection in the telephone line.

c) If the exchange side tests fail, then the concerned line card is to be replaced.

Case 2 Quiet a few number of telephones reported dead

a) In this case confirm from the external plant records whether subscriber belong to the

same distribution cable.

b) In such a situation, the fault can be due to a problem in cable plant itself, which is to

be corrected. Otherwise each line has to treated separately as in case-1

TELEPHONE HELD-UP (NO DIAL TONE)

a) In case subscriber complains of the telephone being held up, then the likelihood is

that speech battery is present but some ground fault is there.

b) To ensure this check the status of the subscriber on BM. If the status indicates INS-

LLO for the line, then confirm the fault by conducting outside plant open loop tests

on the subscriber.

c) If the outside plant test passes then perform exchange side tests and confirm that

there is no fault at the exchange side. If there is a fault in the exchange side then the

concerned line card is to be replaced.

PERMANENT RING

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a) Check the status of the terminal.

b) Perform the exchange side tests on the concerned subscriber. If the exchange side

tests fail, the line card is to be replaced.

c) Perform the closed loop tests on the line. If closed loop tests fail, most likely the fault

will be in the telephone instrument.

d) Perform outside plant open loop test on the subscriber and confirm that there is no

fault at the outside plant.

e) Make check on the other lines in the same TU.

PERMANENT DIAL TONE

a) Check the status of the terminal.

b) Perform closed loop tests on the line. If closed loop tests indicate fault in the

telephone instrument, then the telephone has to be replaced.

c) Perform exchange side tests and confirm that there is no fault at the exchange side.

If there is fault at the exchange side, then the concerned line card unit should be

replaced.

d) If the subscriber has changed his instrument recently. Check the data for proper

instrument type and modify the instrument type if necessary.

SPEECH QUALITY POOR

a) Presence of foreign potential and low insulation may be of the poor speech quality.

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b) Perform outside plant open loop tests on the subscriber. If the tests indicate fault in

the cabling, it has to be retraced and rectified.

c) Conduct exchange side tests also to confirm that there is no fault in the exchange

side. If there is fault at the exchange side, then the concerned line card should be

replaced.

FEEBLE SPEECH

a) The likely cause of this complaint is lower values of the loop current. This can be

confirmed by conducting closed loop tests on the line

b) Conduct exchange side tests also and confirm that there is no fault at the exchange

side. If the there is faulting in exchange side then the concerned line card should be

replaced.

CALL, BEING ROUTED TO WRONG NUMBERS

a) In this case most likely the fault will be in the telephone instrument.

b) Perform the closed loop tests on the line. If the closed loop tests indicate fault in the

telephone instrument, then telephone has to be replaced.

ONE-WAY SPEECH

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a) Perform exchange side tests and confirm that there is no fault at the exchange side.

If there is fault at the exchange side, the concerned line card is to be replaced.

b) Perform the closed loop tests on the line. If closed loop tests indicate the fault in the

telephone instrument, then the telephone has to be replaced.

RINGER CADENCE IS NOT O.K

a) If the problem is occurring on all the lines of that TU, replace PSUI, which is towards

the active copy of TIC. Check the problem is rectified.

b) If the problem is not occurring on all the lines of that TU, then the telephone

instrument must be faulty.

THE RISK FACTOR OF EXCHANGES’ WORK

The work in the few parts of the exchange is very risky. These parts are given below:

Transformer room

Power plant

Battery room

Switching room

TRANSFORMER ROOM:

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In this the voltage is very high i.e. is 11000v coming from the high-tension supply of the

P.S.E.B. Therefore, the single touch to the any naked wire can burn. There is too much risk

so there should be awareness about the equipment in this room.

POWER PLANT:

In the power plant there is the battery room as well as the invertors, which also work on the

AC voltage to touch the any equipment is also dangerous in this room. In the battery room

there is the acid filled in these batteries that is changed time by the time so there is also

dangerous because the single touch to this acid can burn your skin.

SWITCHING ROOM:

There is the high dc voltage in this room so there is also risk to touch these cards of this

switching room. One thing should remember that we should done any process in this room

when we can do that comfort other wise it can damage our body or the any module in the

frame.

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Bibliography

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