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Submitted to-

Department of Computer Science,Govt. Women Engineering College

Ajmer (Raj.)

Presented ByBeenu Chaudhary

University Roll o ! "#$$%CS"

B.'ech. inal ear (Computer Science)

&

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Acknowledgement

The project report on my summer training at BSNL,Bharatpur would not have been efficiently possible without

the kind help and guidance of the training officers of

different exchanges and other office members of the

BHARATPUR BSNL office.

So, I would like to express my gratitude to the

General Manager, BSNL, BHARATPUR who allowed me to

pursue training in his organization. I would also like to thank Mr. S.S Sinsinwar S.D.E.

and Mr. Atul Jain J.T.O., EWSD exchange, Agra. Moreover

I thank all other members who have directly or indirectly

contributed to this project.

Last but not least I extend my thanks to all my

friends, who have always been very supportive and co-

operated me throughout the term of my summer training.

Bharti Chaudhary

*

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Preface

I have written this summer training report as per the

requirement of the Rajsthan technical university for partialfulfillment of the industrial interaction programme after

the 6thsemester.

The report gives an overview of various exchanges

of the communication department of BSNL, AGRA. We

under went training from 13thJune 2011 to 09thJuly

2011. During this duration we visited the E10B, OCB and

5ESS exchanges. I have tried my level best to explain thecomponents and working of all the above-mentioned

exchanges in this report.

Bharti Chaudhary

+

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Contents

Topics Page No.

INTRODUCTION..6 E-10B exchange

OCB exchange

5ESS exchange

TELEPHONE EXCHANGE7

Manual Exchange

Automatic Exchange

TELEPHONE INSTRUMENT......8

Rotatory Dial TypeElectronic Push Button Type

TELEPHONING SYSTEM.....9

POWER PLANT

.14

Float Rectifier

Battery Charger

Switching Cubical

FLOAT SYSTEM

15

OPTICAL COMMUNICATION.

.....16

ADVANTAGE OF OPTICAL FIBRE..

17

MICROPROCESSOR..

.18

BUS SYSTEM..........18

ELECTRONIC EXCHANGE FACILITIES......19

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Facilities to Subscriber

Facilities to Administration

Versatility

Facilities to maintenance Personal

I.D.N.

I.S.D.N.

CONTROL SYSTEM..22

ELECTRONIC EXCHANGE24

Types of electronic exchange

Function of an electronic exchange

TYPES OF SWITCHING

SYSTEM.28

Time division switching system

Space division switching system

SWITCHING PROCESSOR....28

SWITCHING PERIPHERALS..29

LINE INTERFACE....30

Analog Subscribers line interface

Transmisssion interface

Signalling interface

SIGNALING....31

Channel associated signalling

Common channel signalling

BASIC MODULES.33

CENTRE FOR DEVELOPMENT OF TELEMATICS 35

CONCLUSION37

REQUIREMENTS

38

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INTRODUCTION:

From the ancient days it has been deepest human desire to stay closed with

those they need. Many different ways have been evolved and implemented

to fulfill this; Telephony is also such a mechanism that uses Telephone,electronic equipment that converts sound into electrical signals that can be

transmitted over distances and then converts received signals back intosounds.

Electronic echanges play ma!or role in this system. "t#s a workplace

that serves telecommunication facilities where lines from telephones can beconnected together to permit communication. The switching center that

houses the terminating and switching equipment is called TE$E%&'(EE)*&+(E. Following are the types of echanges where upon we have done

training and prepared this report-

/ E10B- This was the first ever fully electronic echange of our country

established in 001. This name stands for Electronic210,111subscribers# capacity2B3series code/. "t had given first ever speeded

dialing feature in telephony.

4/ OCB- This name stands for Optical2Cable2B 3series code/. "t was

established in "ndia in 005. +nd it had first ever introduced conceptsof mobile echange, call tracing, caller "6, "76( etc. in our country

along with significantly increasing the number of connectedsubscribers per echange.

8/ 5ESS- This name stands for 51,111 subscribers# limit2 Electronic2Sub2

Subscribers. "t had implemented concept of sub2subscribers toincrease the subscribers# limits.

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TELEPHONE EXCHANGE

The switching center that houses the terminating and switchingequipment is called TE$E%&'(E E)*&+(E.

'$/$012$ $3C1A4$

%anual e5chan6e Automatic e5chan6e

Cordless Cord 'ype Stro76er Cross8ar $lectronic(0B3 Board) ma6neto s7itch

CB s7itch8oard

Analo6

Di6ital

Fig 1:Types of Telephone echanges

Manual Ec!ange- Manually operated by a attendant

called telephone operator. Automatic Ec!ange-'perated by automatic switching

equipment. "ocal Batter# S#$tem-9attery bar locally provided with

the subscribess for energising the transmitter of theirtelephone for speech service.

Magneto Switc!-:inging was done by a hand generator

producing 5 cps at 5v Magneto type subscriber telephoneinstrument is used with this system which has a hand2enerator set within it.

Central Batter#29attery was provided centrally at

echange and it provided energy to all the telephoneconnected to the echange.

9

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TELEPHONE INSTRUMENT

Telephone instruments are mainly of three types < Magneto Telephone "nstrument4 *.9. Telephone "nstrument8 +utomatic Telephone "nstrument

A%&OMA&'C &E"EP(O)E ')S&*%ME)&

:otary 6ial Type Electronic %ush button Type"%T=55 Type is allowed forElectronic Echange

6.T.M.F. 6ecadic

Fig +:Telephone "nstruments

*otar# ,ial &ele!one -"t comprises three type of circuit3Fig/

. ,ialing Circuit . "mpulse spring produces make breakpulses. 6ial of normal 36'( springs are also provided/.

4. *inging Circuit . "n ringing circuit .> Micro Faradcondensor allows only +.*. ringing current and does notallow 6.*. to flow throw it and thus save energy.

8. Seec! Circuit . Transmitters converts acoustical energyinto electrical energy and receiver converts electrical energyinto acoustical energy.

Pu$! Button e . "n decadic dialing make break pulsesare generated and in dual tone multi2frequency 36TMF/ isgenerated by miing of two frequencies from two sets offrequency one set of lower and other set of higher frequency3fig24/.

#

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,ifference /etween ,&MF ,ecadic ,ialing

,ecadic ,ialing ,&MF ,ialing

Make break pulse dialing

7tore dialing.

6ialing speed slow 1.>

digits per second.

6ifferent digits take

different times in dialing.

Frequency dialing.

"nstantaneous dialing.

6ialing is faster, 5digits

per second.

7ame time is consumed in

dialing any digit.

TELEPHONING SYSTEM

Telephonic 7ystem can be divided into two parts 3fig28/

'nternal . Echange side equipment fall in this category suchas 11,111, ?11 pairs.

D.0.

2;1

CAB

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ABBREVIATIONS USED IN TELEPHONE EXCHANGE

PCM Pulse code modulationSSTD Subscribers trunk dialing

OTD Operators trunk dialing

ISD International subscribers dialing

FAX Facsimile auto Xerox

TAX Trunk auto exchange

PCO Public call office

IDN Integrated digital network

ISDN Integrated service digital networkCBNM Central battery non multiple

CBM Central battery multiple

PABX Private auto branch exchange

PBX Private branch exchange

PMBX Private Manual Branch Exchange

EPABX Electronic Private Auto Branch Exchange

ALU Arithmetic Logic Unit

LDCA Long Distance Charging Area

SDCA Short Distance Charging Area

CDOT Center for Development of Telematics

LAN Local Area Network

WAN Wide Area Network

E-MAIL Electronic Mail

I-NET Computer Network within Land

INTERNET International Computer Network

TELEX Telegraphic Exchange

CTO Center Telegraph Office

DTO District Telegraph Office

SPC Stored Programme Control

DTMF Dual Tone Multi Frequency

RAX Rural Auto Exchange

&&

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&*

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Fig : Barious types of cross points

Barious types of cross points have been evolved, but sealedcontact type reed relays are commonly used in analog switchingnetworks. Memories are preferred. + basic switching stage consists of reed relay arranged in arow and columns in the form of a matri. 7everal such stagesconnected in tandem constitute a switching network. There are

two types of switching network viA. Cnidirectional and bi2directional. Transit echanges are unidirectional network.Dhereas the subscriber local echange are bi2directionalnetworks.

,'2'&A" S3'&C(')2- 6igital switching has become asynonym for time division multiple. "n digital switching system,

&+

CROSS

POINT

$/$C'R2 %$C1A

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digital signals are switched in two nodes, time switching andspace switching. Time switching basically involves rearrangementof channel sequence in the same %*M from whereas spaceswitching involves interconnection of same channels of a different%*M high way. "n a practical digital switching both time andspace switching stage is employed to increase the traffic handling

capacity of the switch at minimum cost. +mong the variouspossible combinations T7T structure is most commonly used. 7ynchroniAation of various echangeclocks in a digital network is essential to provide requiredservices. *ausing a slip due to mismatch between the clocks willresult in multination of information and description of services.&ence, slip has to be controlled using plesiochronous andsynchronous approaches.

MO,%"A&'O): 'ften the message signal is not suitable fortransmission over the medium in its original forms. Therefore,the message signal is located in a carrier wave, which is moresuited for transmission over the medium. This process is calledmodulation of the carrier wave. +t the receiving end station themessage signal received back from the incoming modulatedcarrier wave by a process is called demodulation which is inverseof modulation.

M%"&'P"E6')2:Modulation enables multiple message signalsto be simultaneously transmitted over the same medium withoutinterfering each other. Transmission of multiple message signalssimultaneously over a medium is called multipleing. Modulation is essentially a process of relocation of amessage signal in a carrier wave, which is more suitable fortransmission for transmission over the medium than the messagesignal itself.Three types of modulation can occur2

. +mplitude modulation4. Frequency modulation8. %ulse modulation

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PO3E* P"A)&

'ne of the primary requirements of any computer system is thatservice will be available to the subscriber at any time. "n the vastma!ority of echanges the electrical energy required forsignaling, switching, speed transmission mains. The echangepower system is designed to provide continuous anduninterrupted telephone service even when the public electricfails. De can divide power plant in three ma!or blocks such as

FLOAT RECTIFIER

BATTERY CHARGER

SWITCHING CUBICAL

F"OA& *EC&'F'E*S: 2 "t constitutes one item of telephone

echange power plant. The function of float rectifier is to drivepower supply +.*. mains and deliver to the telephone echangeequipments continuous and filtered 6.*. supply at nominalvoltage of 1 volt 3actual terminal voltage is . volt/. Thevoltage of supply is to be maintain with closed limits of 21.volt unvarying impact voltage and output load currents, on set ormore batteries are normally floated across the float rectifier inparts are as follows 82phase step down transfer

&alf controlled 8phase bridge rectifier

Filter circuit and controller

BA&&E*7 C(A*2E*- "t is a part of power plant in an echangeand provides initial, refresher and boost charging for thebatteries. The 4? lead acid cell battery can be charged from.>B per cell to 4.5 volt per cell.

A8C8 ')P%& 81B, 851B, 801B, ?1B, ?81B2 1

1*ps24*ps

82phase ?wire system

,8C8 ')P%& For 4? cells charging

??volt to ?volt at 1 +mpere

? volt to = volt at 5 +mpere

&-

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COMPO)E)&S 82phase step2down main transformer

9allast chokes

8phase full wave rectifier

S3'&C(')2 C%B'CA":2

"t provides facility for

Floating any one or more batteries

*harging any one battery at a time

7upervisory alarms for all associated units

"ncorporates auto2paralleling panel, which contains the

circuiting for sequential switching i.e., for switching G'(# andG'FF# automatically to suit echange load one or more floatrectifiers whose output are in parallel."n case where echange load is met directly from the mains,provision is also made for alternate source of supply in the eventof mains failure .The emergency energy is derived from

9attery of secondary cells.

+ combination of batteries of secondary cells and primemover generator sets. 7econdary cell or accumulators used in department aremostly of bad acid type and hard rubber container

&

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F"OA& S7S&EM: "n this system the battery supplies only theemergency reserve requirements of the equipments duringmains failure. The battery is always kept connector across theload in the float system in a fully charge state but the

operating conditions are so maintained that the floatedbattery does not discharge in to the load as long as the mainspower supply is available. +s soon as the mains fail thefloated battery takes the load of the each. Thus there isabsolutely no break in 6.*. power supply when the mainspower supply fails.

Barious forms of standby supply arrangements are available, outof which the engine generator sets are most common. Thisconsists of two separate machine an engine and the other

generator or alternator. + generator is an electromagneticmachine, which converts natural form of energy to mechanicalenergy.+ diesel engine is an internal combustion engine, which operateson liquid fuel.

OP&'CA" COMM%)'CA&'O)

'ptical fiber is a latest means by which we transmit information3speech, data, video/, in the form of light through optical fibers3fig. /. This communication requires five stages.

"nformation is converted in to electrical signals by encoder.

Electrical signals are converted in to optical signal by means

of a light source. 'ptical signals are transmitted to the distant station

through optical fiber media.

+t the distant station optical signal are again converted in toelectrical signal by means of detector. The electrical signal is further converted in to information

3speech data and video/ by means of decoder at the distantstation.

&9

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'ptical fibers have following two parts *ore 3"nternal part/

*ladding 3'uter periphery/

'ut surface of cladding creates a difference in refractive indedue to which total internal refraction phenomenon happens incentral core. *ore and cladding made of transparent substancelike silica or 9orosilicate, but the refractive inde of cladding isless than core.

A,9A)&A2E OF OP&'CA" F'B*E Thousands of circuit can be provided through optical fiber.

The cable is less in siAe and diameter and so easily

transportable. (oiseless circuit can be provided through this media

There is no risk of fire, electric shock and short2circuiting.

There is no effect of ecessive temperature on it

:epeaters are provided at long intervals and repeater less

chain is also possible.

Fig 5:'rganiAation of typical microcomputer

%

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Microroce$$or

+ microprocessor is a comple electronic processor on a single

silicon chip 3$arge2scale integrated circuit/. "t is capable ofperforming arithmetic and logical functions under the control ofprogram.Functional units of microprocessor2. +rithmetic and logic unit4. :egisters 3Temporary memory/8. Timing and control unit

Function$. FET*&4. 6E*'6E8. E)E*CTE

Bu$ S#$temBarious switching peripherals are connected to central processor

by means of a common bus system. + bus is a group of wires onwhich data and command pulses are transmitted between the

various sub units of a switching processor and switchingperipherals. The device to be activated is addressed by sendingits address on address bus. The common bus system avoidscostly interconnection among various devices 3Fig2=/.

Addre$$ Bu$-The address bus normally consists of = lines. To access aparticular device or memory location, the microprocessortransmits its address on these lines.

,ata Bu$-The data bus usually has parallel conductors. "t is a path fortransferring data in and out of the processor.

+ddress bus is unidirectional and data bus is bi2directional.Control Bu$-*ontrol bus is used for transmitting and receiving control signalsbetween microprocessor and various "H' devices.

&:

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Electronic Ec!ange Facilitie$

Electronic echange facilities can be divided in three ma!or

groups2. Facilities to subscribers4. Facilities to +dministration8. Facilities to maintenance personal

Facilitie$ &o Su/$cri/er-

MF* %ush 9utton 6ialing 3 6TMF dialing/

%riority subscriber lines

Toll 3outgoing call/ detraction

7ervice interception +bbreviated dialing

*all forwarding

6o not disturb

*onference call

*amp on busy

*all waiting

*all repetition

Third party inquiry

%riority of calls to emergency position

7ubscriber charge indicator

*all charge print out or immediate billing

Malicious call identification

"nterception or announcement

*onnection without dialing

+utomatic wake2up alarm service

&ot line or private wire

6enied incoming call "nstrument locking

Free of charge call

*ollect call

*"

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Facilitie$ &o Admini$tration-

:educed switch room accommodation

Faster installation and easy etension

Bersatility

9er$atilit#-. +dopting various signaling and call charging pattern4. "ncrease facilities in rating and numbering by simple

commands8. M+(+EME(T F+*"$"T"E7- +utomatic billing, centraliAed

supervision and maintenance, automatic load control andtraffic data recording and analysis

?. Dide range of subscriber services. Dide range of dial speed3 to 44 digitsH second/=. Easily handling of group line 3%9)/5. Cnlimited possibilities for line translation, digits storage and

route analysis>. *ompatibility with new techniques in signaling an data

switching

Facilitie$ &o Maintenance er$onal- +utomatic fault processing 3&ardware checking/

+utomatic changeover to standby unit in case of fault in one

unit 6iagnosis

7tatistical programme

9locking facilities

'verloading security

'8,8) 'ntegrated ,igital )etwork;-".6.( is a network in which both the transmission media andswitches employ digital techniques. This network combines the

advantages of both switching and transmission. "n this system,speech signals are converted to digital signals at transmittingand receiving stations. This system has easy maintenance andsupervision, which is carried through computers. This enablesmore fleibility in terms of remote controller and subscriber unitsand reserved in saving of circuit cost.

*&

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'8S8,8) 'ntegrated $er

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Control S#$tem

+ system can perform any work by a single processor ormultiprocessor.

Fig =:Functional 6ivision I 7egmenting

Functional ,i/. %rocessors when 7egmenting is used

*+

Control System

Sin6le 0rocessor System (%onarchic)

%ultiprocessor System (Distri8uted Control)(2li6rachic)

2ne level System 1ierarchical System

unctional Division Se6mentin6 2 Levels 3 Levels

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P1 P2 P3 PN

F1 P1

F2 P2

F3 P3 %rocesses

XGE whenFunction function

division is used

Fn %n#

Cltimate capacity of )E

Fig >:Functional 6ivision I 7egmenting

To switching network

Fig ?: &ot 7tandby

)@1 *edundanc#- one unit is etra added in parallel with (units. "n the failure of any one unit, this etra unit takes the loadof the failed unit, but if two units will fail, the echange cannotwork 3fig 0/.

*

+ +4 9 94 ( (4

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S#nc!ronou$ relica dulication- the standby unit is alwaysconnected and compared by a clock pulse. "f there is a differencein two units, it means one unit is faulty 3fig 1/.

Electronic Ec!ange

These are entirely computeriAed and electronic devices, whichwork on store programme control. Electronic logic componentcan do ten thousand times operation during signal in thecomparison of electromechanical echange.

"n an electronic echange a single control devicesimultaneously process a number of calls on time2sharing basis.7uch centraliAation is more economical, but it is disadvantageousin making switching system more vulnerable to system failure.This, however, can be overcome a standby control devices. These electronic echanges have powerful processing unit.%art of control equipment capacity utiliAe for function other thanfor processing. There are two types of electronic echange.

Analog Ec!ange- this echange uses one physical path for onecall. &ence, full availability could not be achieved due to internalblocking.

To switching network

*-

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CC

Fig :( :edundancy

*lock

*opartor

Fig 10:7ynchronous :eplica 6uplication

,igital ec!ange- digital switching enables sharing a single

path by several calls. &ence, it provides full availability and thereis no change of internal blocking.

Function of a electronic ec!ange The primary purpose of an echange is to provide atemporary path for simultaneously bi2directional transmission ofspeech between

*

MA MB

A BC

~

TELEPHONE ENVIRONMENT

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. 7ubscriber lines connected to the same echange 3localswitching/

4. 7ubscriber lines and trunks to other echange 3outgoingtrunk calls/

8. 7ubscriber lines and trunks from other echange 3incomingtrunk call/

?. pairs of trunks towards different echange 3transitswitching/

These are called the switching function of an echange andare implemented through the equipment called the switchingnetwork. +n echange which can set up the !ust first three types ofconnection is called a subscribers of local echange it is called atransit or random echange.

'ther distinguish function of an echange. Echange of information with the eternal environment

3subscriber#s line or other echange/ that is signaling.4. %rocessing and signaling information and controlling the

operation of switching network that is control.8. *hanging and billing.

+ll these function can be provided more efficiently using

computer controlled electronic echange and functional divisionof a store programme. *ontrol electronic echange can be givenas 3fig /

$ine I Trunk Terminal Equipment

*9

Switching

Network

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9C7

7witchingprocessor

Fig 11: Functional 7ubdivision'f an 7%* Echange

*#

DistribtorSc!nner M!rker

Co""onCh!nne#

Sign!##ing

ter"in!#

Ch!nne#Associ!te$

Sign!##ing

ter"in!#

Central

Control%%%%%%%%%%%%%%%%

Me"ories

M!n%M!chine Di!#oge&eri&her!#

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. &erminal euiment- it provides an individual basis foreach subscriber#s line and for inter echange trunk.

4. Switc!ing network- the main function of switching issetting up the temporary connection between two or moreechange termination and transmission of speech and

signals between terminations with reliable accuracy.

e$ of $witc!ing $#$tem

There are following two types of switching system in "ndia3a/ Sace di

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Central Control

"t is a high2speed data processing unit that controls theoperation of the switching network 3fig 4/

Programme Store-in this, set of instructions called programme

are stored. The programmes are interpreted and eecuted by thecentral control.

,ata Store- it provides for the temporary store of transientdata, required in processing calls such as digits dialed bysubscribers, busyHidle status of lines and trunks e.t.c.

6ata 7tore is temporary memory whereas translation andprogrammes stores are semi permanent type. The information insemi transparent memory does not change during the processing

of call but the information in data store changes the continuouslyorigination and termination of each call.

Switc!ing eri!eral$ The time intervals in which the processor operates is in theorder of micro second, while the components in telephoneswitching system operate in millisecond. The equipment knownas switching peripherals is interface between two equipmentworking at different speeds. The interface equipments act asspeed, buffer as well as enables conversion of digital logic signalsfrom the processor to the appropriate electrical signal to operaterelay cross points etc scanner, distributor and marker fall underthis category of devices.Scanner-its purpose is to detect and inform the central controlof all significant events on subscriber lines and trunks connectedto the echange.Marker-it performs physical set up and release of paths throughthe switching network under the control of central control.,i$tri/utor-it is a buffer between high speed, low power centralcontrol and relatively slow speed high power signaling terminalcircuit.

+"

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"ine 'nterface

To enable an electronic echange to function to the eistingoutdoor telephone network certain interfaces are required

. +nalog subscriber line interface4. Transmission interface8. 7ignaling interface

Analog $u/$cri/er line interface-

The function of a subscribers line interface for each two2wire lineis often known by the acronym K9':7&*TL which is

92 9attery Feed'2 'verload %rotection:2 :inging72 7upervision of loop status&2 &ybrid*2 *'6E*T2 *onnection to test equipment

+ll these functions cannot be performed directly byelectronic circuiting so, suitable interfaces are required.

&ran$mi$$ion 'nterface- transmission interfaces betweenanalog trunks and digital trunks such as +Hd and 6H+ convertersknown as *'6E*. These may be provided per line and per trunkbasis 3 on the basis of one per 81 speech channels/.

Signalling 'nterface2 + typical telephone network may havevarious echange systems 3manual, stronger, crossbar andelectronic e.t.c./ each having different signaling schemes. "nsuch an environment an echange must be in accordance withseveral different signaling codes.

+&

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Signaling

There are four types of signaling possible- 2. :ing 6own 7ignalling4. 6* signaling8. E I M signaling?. 6igital signaling

6igital 7ignalling can be performed in two ways- 2

C!annel A$$ociated Signalling-"nitially all signaling betweenautomatic echanges was decadic i.e. telephone numbers weretransmitted as trains of to 1 pulses, each train representingone digit. To increase the speed at which the calls could be set upand to improve the reliability of signaling, compelled sequencemulti frequency signaling system was then introduced. "n thissystem each signal transmitted as a combination of two out of agroup of say or = frequencies. "n both decadic and multifrequency systems the signal for each call are sent over achannel directly associated with the inter echange speechtransmission circuit is used for that call. This is termed as

channel associated signaling.

Common C!annel Signalling2 recently a different techniquehas been developed known as common channel signaling. "n thistechnique all the signaling information for a number of calls issent over a signaling link independent of the inter2echangespeech circuit. &igher transmission rates can be utiliAed to enableechange of much larger amount of information. This results infaster called set up. "ntroduction of new services i.e. abbreviated

dialing and more retrials ultimately accomplish higher callcompletion rate. Moreover it can provide network managementand traffic engineering.

+*

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To switching (etwork

Fig 1+: *entral *ontrol

*onfiguration and is based on 84 channels %*M structure. "t usesa basic rate of =? kilo bit per second and 4 mega bit per second .

%rimary multipleing control is distributed over the system byusing = bit microprocessors. +ll the critical control circuitry asbuilt in redundancy. 7ystem hardware utiliAed advanced conceptsin microelectronics for a compact and optimum design. 9asicmemory unit has been implemented as 4 mega bit dynamic :+Mbased with 4= kilo bit as the basic dynamic :+M chip.7ingle chip digital signal processors are used for implementing6TMF and MF receiver.

+ high performance, high densityB$7" chip detects multiple tones simultaneously performs signalfiltering on four channels. This approach reduces costs, powerdissipation and saves space on %*M. +nalog to digital conversionon the line circuit has been achieved by using a per channelcoder decoder 3*'6E*/ chip.

++

*entral *ontrol %rocessor

%rogramme 7tore

Translation7tore

6ata 7tore

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BAS'C MO,%"ES

. 9ase module 3Fig 8/4. *entral module8. +dministrative module?. "nput output module

PA*& OF BASE MO,%"E

. Terminal units for interfacing analog lines and trunks andproviding special circuit.

4. 6igital terminal unit < for interfacing digital trunks.8. Time switching unit 2 for message switching and provision

of service circuit.?. 9ase processor unit 2 for control message, communication

and call processing function.

CA*,S ') &E*M')A" %)'&

. $ine circuit card.4. +nalog trunk card.

8. 7ignalling processor card 2 scanHdrive function originationdetection, answer detection, digital detection analysistransmission and several detection.

?. Terminal interface card.

&'ME S3'&C( %)'&

"t has a time switch for time switching within the basemodule, a message switch for controlled message communicationwithin the base module and between base module and a serviceunit for providing call processing support. $ike MFH6TMF circuits

+nswering circuits and tones e.t.c. 4> channel multipleingcircuits and = bit microprocessors.

BASE P*OCESSO* %)'&

+

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. *.%.C card.4. 9ase interface controller card 39.".*/.8. 9us interface device 39.".6/.?. Memory unit 3M.C/.

CE)&*A" MO,%"E

"t is responsible for space switching of inter module calls andcommunication between base module and administrative module.

/

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CENTRE !R "E#EL!P$ENT ! TELE$%T&CS

S'STE$ E%T(RE ! C."!T

7ingle frame terminal unit capable of 4> terminations7tored program control(on blockingMaimum 4? trunksModular growthMan machine communication

$ow power consumption(o air conditioning required(o signal fault effect more than > terminationsEasy installationFleible system dimensioning"ndividual subscriber meter up to , 11,111 units

S'STE$ %RC)&TECT(RE

Terminal groups? nosTerminal interface? per terminal group

'ne terminal interface has > terminations of pairs 3fig ;/+nalog information over the termination are first change

to digital format at the bit rate of =? bit per second. 7uch 84channels %*M from the? terminal interfaces are time division

multipleed to generate 84 %*M link with the data rate of 4.1?>Megabyte per second thus from = terminal interfaces De get the?%*M 84 link which are connected to the switching network.

SW&TC)&NG NETW!R*

The switching network is completely non2blockinnetwork and allows for higher traffic handling capacity. The ?%*84 links from terminal groups undergo time division multiplein

T6M to generate %*M 4> channel link at bit rate of > megabit psecond. +fter switching the channel 4> %*M channel link i

demultipleed to regenerate ?%*M 84 links at 4 megabit psecond, which carry the switched information back to the termininterfaces.

+

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S&GN%L PR!CESS!R 7ignaling information as the dialed digits,ring trip, trunk seiAure etc is separated at the terminal interfacesand carried to 7% on a time2multipleed link. The 7% passes onthis information to the T.".* similarly, T.".* uses 7.% for effectiveany device in the terminations.E.g. ringing current.

TER$&N%L &NTER%CE C!NTR!LLER"t drives the identities of the calling and the called terminals

and stabiliAes a path through the switching network betweenthese terminals. The T.".* communicates with the :.*.% on thehigh data link controller 3&.6.$.*/ link for all call relatedinformation.

R.%.+ C!NTR!LLE" PR!CESS!R ,R.C.P. "t is a microprocessor2based processor, which handles the callprocessing function. :.*.% stands the terminal connection relatedinformation to the T.$.* over the &.6.$.* link.

$%NTEN%NCE P%NNEL "t is connected to :.*.% viA :7484* link for system for

operation and maintenance function + 6*2to26* converter generates the various voltagesrequired for the system operation and also provides ringing forthe subscriber loop. *6'T :+) uses integrated circuit based on metal oidesilicon, M'7, *M('7 low power schottkey transistor. "n,Transistor logic bipolar 1 types of cards are used.

+9

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,A&A P*OCESS')2 PE*'P(E*A"S. Man machine dialog terminal

a. Tele type writerb. Bisual display unitc. %rinter

4. 7pecial purpose peripherals employed for carried out repeated

function such as subscriber line testing which requires highspeed.8. &igh2speed large capacity data storage

a. Magnetic tape driveb. Magnetic disk unit

These are used for loading software in processor memory.

?. Maintenance peripheral27uch as alarm initiator special console

are used primarily to indicate that automatic maintenanceprocedures are failed and manual attention is necessary.

CO)C"%S'O)- The electronic echange work on the principle of storedprogram control 37%*/. +t the call processing are performed onthe basis of a pre designed program which is stored in thememory of a central processor. Though the initially designedelectronic echange had single centraliAed processor, the control

is being decentraliAed providing dedicated microprocessorcontrolled subsystem for improved efficiency and security of thesystem. This modular architecture also adds future epansion.

+#

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RequirementsA.TER$&N%L &NTER%CE

&.'erminator card

*. Su8scri8er line card ( 7ire trun@)

+. /oop trun@ card (t7o 7ire trun@)

B.SER#&CE C&RC(&T&.Conference card

*.'one 6eneratin6 card (dial tone, 8usy tone, num8er

unattaina8le tone, rin6 8ac@ tone conference idle tone, RA3test tone, idle tone not used ton

C.T&$E SW&TC) %N" C!$$!N C!NTR!L

&. '.

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INTRODUCTION:

From the ancient days it has been deepest human desire to stay closed with

those they need with. Many different ways have been evolved and

implemented to fulfill this; Telephony is also such a mechanism that usesTelephone, electronic equipment that converts sound into electrical signals

that can be transmitted over distances and then converts received signalsback into sounds.

Electronic echanges play ma!or role in this system. "t#s a workplace

that serves telecommunication facilities where lines from telephones can beconnected together to permit communication. Thus the switching center

that houses the terminating and switching equipment is called TE$E%&'(EE)*&+(E. Following are the types of echanges where upon we have done

training and prepared this report-

1; E10B-

+; OCB-4; 5ESS-