B-tech - Bsnl Deep

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DEPARTMENT OFELECTRONICS AND COMMUNICATIONS

E-10B EXCHANGE

D-TAX 285 EXCHANGE

SUBMITTED TO: SUBMITTED BY:

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CERTIFICATE

This Practical Training Report entitled “E10B switching system and

D-TAX OCB 285 system” is being submitted by Bright batch

as a report of the work undertaken by them at Bharat Sanchar Nigam

Limited . This work is the result of the student’s own effort, and was

undertaken by them at the end of the VI semester.

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ACKNOWLEDGEMENT

On behalf of the supreme lord, I take upon the privilege to extend my sincere

and heartfelt thanks to all the manifestations of the Almighty without which

the successful completion of this project was just impossible.

I am highly grateful to Mr. J.M. Sanalia (S.D.E.,BSNL, S’nagar) who was

kind enough to consider my choice and place me in OCB D-Tax switching

Dept. and gave acknowledge to regarding system.

I am very thankful to all the staff of BSNL, especially Mr. Prafull P.

Yenorkar, Mr. P. M. Dave, Mr. R. K. Raval who shared their valuable

time to guide me.

DEEP PATEL.

ABSTRACT

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The aim of my training is to understand the basic concepts of the E10-B Switching

System. During training I have learned the basic functioning of the exchange . I have also

learnt the whole routine of making a call from one user to another user in different circle.

I have also learnt some basic concepts of optical fiber communication .i have seen the ofc

transmitter which connects the s’nagar exchange to a’dbd exchange and calculated the

bandwidth as 64gb/sec.

I have learnt the basics of MDF(main distribution frame) ,which connect exchange end to

subscriber end. Here the line side (subscribe end ) pair cable terminating at one side of tag

block and the exchange side pair cable terminating at other side. Now both are connected

with jumper pair cable. Jumper pair cables provide more flexibility to connection and

make easy operation of testing the line

During training I have also learnt how to check any number and repair it from the

exchange end.

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Index

E-10B EXCHANGE

CHAPTER 1

INTRODUCTION…………………………….……….91.1 The PCM System………….…………………………………...9

1.2 System Structure……………………………………………….9

CHAPTER 2

CONNECTION UNIT…………………….……………112.1 Subscriber Connection Unit...…………………………………. 11

2.2 CSE……………………………………………………………..11

2.3 URM……………………………. ……………………………..11

2.4 ETA…………………………………………………………….12

CHAPTER 3

SWITCHING NETWORK…………….…………….. 123.1 CX………………………….…………………………………. 12

3.2 Function………………...……………………………………. .13

CHAPTER 4

CONTROL UNIT…………………………………. 134.1 TR..…………………………………………………………… 13

4.2 MR……………………….…………………………………… 14

4.3 TX……………………………………………………………...15

4.4 MQ……………………………………………………………..15

4.5 OC……..……………………………………………………….16

4.6 DSF…………………………………………………………….174.7 OMC…………………………………………………………...17

4.8 Facilities in E-10B…………………………………………….18

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CHAPTER 5

OCB………………………………….. 17

5.1 Introduction……………………………………………..… 20

5.2 Salient features of the system…………………... 205.3 Subscriber facility provided by the system…………… 22

5.4 The switch concept…………………………......................... 24

5.5 Common Channel Signaling……………………………….. 24

5.6 Architecture of OCB-285………………………………... 25

5.7 Functional architecture of ocb……………………….. 26

5.8 Hardware architecture of ocb……………………… 27

CHAPTER 6

MAIN DISTRIBUTION FRAME………………. 316.1 Introduction ………………………. 31

6.2 Vacuum glass Tag block…………………………………. 31

6.3 T-Fuse tag block………………………………. 32

6.4 Testing the lines……………………. 32

6.5 Change number announce reminder…………………………33

CHAPTER 7INVERTER …………………………………. 347.1 Introduction ………………………………………… 34

7.2 Inverter Power section……………………………………….35

7.3 Driver card……………………………………….. 36

7.4 Dc-Ac converter card……………………….. 37

7.5 VRLA batteries……………………………………………. 40

7.6 SMPs batteries……………………………………………. 43

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INTRODUCTION

BSNL

“BHARAT SANCHAR NIGAM LIMITED” is abbreviated as BSNL. It is fourth largest

department of Telecommunication Company in Asia and seventh in world today.

This is one of the most earning revenue in India. Above more than 3 laces employees,

officer and engineers working in BSNL at present.

Previously electro mechanically exchanges for use in India namely

Strowger type exchange, cross bar exchange were there.

These manual telephone exchanges suffered from some disadvantages. To overcome

these an automatic exchange was introduced in this system.

In 1980’s PITHROTHA LTD. Introduced “ C-DOT ” exchange in India. These

exchanges replaced by electro mechanical exchange.

These exchange which has wide range of capacity replaced electro mechanical

exchange, C-DOT-128, C-DOT-256, C-DOT-512, C-DOT-1024(SBM) exchange, C-

DOT-2048(MBM) exchange and so on.

Besides C-DOT exchange ILT exchange, E-10B exchange also proved of mild stone

in Telecommunication Sector to replace electromechanical exchanges, which

were most sophisticated and modern latest techniques electronics exchanges.

There after it was OCB-283 exchange which proved very important exchange in this

series to replace electro mechanical exchanges.

Now it is “WLL” & “GSM” mobiles which is also proved a mild stone

in Telecommunication sector. It was 31st

march 2002 when BSNL started these

GSM mobile and today it has provided almost 35 lacks mobiles in all over

country. WLL system which is also a mobile with limited mobility in city & can have

Tele communication facility in that area almost. While GSM can cover all cities of

the country. DOT provides the following facilities :

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• Telephone services such as Local calls, Trunk calls, Overseas calls etc.

• Wireless services including mobile wireless services for police, defense,

metrological departments, etc

• Renting of Broadcast & TV channels

• Telecom Bureau Services

• Data Services

•FAX Services

• Telecom factories to manufacture telephone switching boards and accessories at

Bhilai, Mumbai, Calcutta and Jabalpur.

• I.T.I. Bangalore for the manufacturing for the carriers, VFT, Coaxial and

microwave equipment.

• I.T.I. Gonda for the manufacturing of E-10B electronic exchange

equipment.

• Hindustan Cables LTD. Hyderabad & Rupnarainpur for manufacturing

underground cables.

• Hindustan teleprinters LTD Chennai for manufacturing teleprinters.

Local telecom network at the metropolitan cities of Mumbai and Delhi are

under the MTNL(Mahanagar Telephone Nigam Limited). Its Corporate office is at

Delhi.

Hence Telecommunication sector has changed our life style today entirely and

today it seems that world has become very small.

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E10B-EXCHANGE

CHAPTER 1: INTRODUCTION

1.0 DIGITAL TIME DIVISION SWITCHING SYSTEM

The E 10 B system has been developed in terms of an integrated telephone network, rather than in terms of individual telephone exchange.

It shares two fundamental principles with the original Platon exchange:

• Use of digital PCM techniques

• Separation of the switching function (at exchange level) from the management

functions (at network level).

1.1 THE PCM SYSTEM: -

The E 10 B system has been developed for 30-channel PCM operation but it can also

handle 24 channel PCM system. When the Platon exchange went into service PCM

techniques could only housed over relatively short distances of a few tens of kilometers.

PCM techniques are now, however, competitive with the most highly developed analogue

transmission techniques.

Optical fiber and digital microwave links will enable PCM techniques to be used on trunk

and international links leading to integrated networks at national and international level.

PCM techniques are currently being used for satellite communication with multiple access

and demand assignment.

Time-Division Multiple Access (TDMA) suggests that full integration of satellite

communication into the terrestrial network, using TDMA-PCM techniques, is a viable

proposition.

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1.2 SYSTEM STRUCTURE :

An E 10 B switching center can be divided into 3 main sections:

The operation and maintenance center constitutes a fourth block, which is shared by a

number of switching center.

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CHAPTER 2 : CONNECTION UNIT

2.1 SUBSCRIBER CONNECTION UNIT:

The subscriber connection unit is the CSE 1000 electronic line concentrator.

This provides for concentrating the traffic on 2,3 or 4PCM links, corresponding to a

maximum configuration of 120 circuits. The interface with the subscriber lines is via

circuit board comprising 16 ordinary subscriber equipment.

The control unit is microprocessor based and is duplicated for reasons of security. The

Multiplex connection unit (URM) is connected to incoming PCM links from distant

concentrators, time-division exchanges and space division exchanges.

In this case analog to digital conversion is necessary and where applicable, the matching

of signaling .Each URM has a total capacity of 32 PCM system. Each URM is housed in

one standard rack and consist of 8 modules each with 4 PCM.

2.2 CSE:

The subscriber connection unit consists of three sections:

• A subscriber connection and concentration section

• A transmission section

• A duplicated control and exchange logic section.

2.3 URM:

A multiplex connection unit is the PCM connection interface between an E 10 exchange

and distant connection units or circuits from other electronic exchanges.

FUNCTION:

The various function of a URM can be grouped under three main headings the following

table;

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• Transmission and reception of 30-channnel PCM links.

• Extraction and insertion of signaling bytes.

• Operational defense and security.

2.4 ETA:

The frequency sender and receiver units generate the tones directly in digital form. These

groups also house the digital frequency receivers used for subscriber and trunk circuit MF

signaling.

FUNCTION:

• The ETA is reception of multifrequency signaling pushbutton dialing signals and

circuit testing frequency in the Frequency Receivers.

• The ETA is generation of the usual tones MF signaling and circuit test frequency

from the tone generators.

• The ETA setting up conference call connection using the Conference Circuits.

SWITCHING NETWORK:

The time-division switching network is a 3-stage system (time space-time: TST).It

provides 4-wire switching between the time slot allocated to the calling party and the time

slot allocated to the called party. When the ultimate capacity is reached the E 10 B

switching network can handle 384 PCM system, 16 of which can be allocated to frequency

sender/receiver (ETA).

The remaining 368 PCM system provide 368*30=11,040 time slot catering for 5,520

simultaneous calls.The switching network is modular by steps of 64 PCM system. The

maximum capacity-switching network is housed in 4 standard racks.

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CHAPTER 3 : SWITCHING NETWORK

3.1 CX:

The switching network is a 3-stage TST switching network comprising a Space-division

multiplex connected between two Time-division switching stages.

FUNCTION:

• It is connected to the input lines (LRE) from the connection units and to the output

lines (LRS) going to the connection units.

• The switching network is connected to the multiregisters, markers, charging units

and monitoring.

LRS LRE

CONTROL UNIT:

The switching operations carried out in block 1 and 2 are monitored by the control units,

which constitute block 3.

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Time-

division

switchin

Space-

division

multiple

Time-

division

switchin



CHAPTER 4: CONTROL UNIT

4.1 TR:

Two translators contain the subscriber and trunk circuit files with all discriminatory data

correspondence between directory number and equipment number, classes-of-service,

trunk groups, charging rate, etc. Each translator occupies one standard rack.

FUNCTION:

• The translator provides the multiregisters on request data on the subscribers and

the circuits required to setup and release calls and other function:

• Translates prefixes and the first digits received from the calling party.

• Translates called party directory numbers into equipment or trunk circuit numbers.

• Controls services such as call forwarding abbreviated dialing hot line recorded call

automatic make up service etc.

Control

Units

14

Exchanger

Module 0

Module 1

Module 2



4.2 MR:

Calls are set up and released by the multiregister which operate in traffic-sharing mode. A

multiregister is microprocessor-based and comprises random access memories which form

the registers, each multiregister houses 256 register.

The minimum capacity required two multiregister, for reasons of security. Six

multiregisters are sufficient for a complete exchange, handling 52 call attempts every

second, in busy hour condition. Each multiregister occupies one standard rack.

FUNCTION:

• The multiregister is responsible for the setting up and releasing of calls. To

implement these two function :

• Takes control of calls and on hook conditions of subscribers and trunk circuits

detected by the connection units.

• Releases subscribers and trunk circuits.

• Receives and retransmits 16-digit dial or pushbutton dialing signals.

• Request the address of the two subscribers

• Controls the sending out of various signals and tones.

CX

Other

Units

4.3 TX:

Two charging units generate the data required for invoicing subscribers.

General or detailed billing is prepared, as required by the subscriber. On the basis of the

rate applicable to a call, as supplied by the translator, the charging unit generates and

totals metering pulses which takes into account the date, time and charging mode. Each

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RegisterExchanger

I/O

Interface



charging unit occupies one standard rack.

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FUNCTION:

• The TX is locates a charging register and allocates it to a call at the beginning of

the speech phase releasing it at the end of this phase.

• The TX is receives metering pulses from trunk circuits.

•

It controls the sending out of tones and various signals (subscriber private meter).

CX

Other

Units

UR URM Switching

Circuits Network

Circuits Network

4.4 MQ:

Two markers handle the routing of data between the various units within the exchange.

The marker is responsible for routing the principle switching message between the various

units of an exchange such as MR,Switching Network.

FUNCTION:

• The marker is receiver new call subscriber and trunk circuit on hook indications

from the connection unit.

• Subscriber and ancillary equipment tests.

• Controlled stop and start surveillance of subscriber calls and trunk circuits.

• Send messages to and receives messages from the OMC.

Other Switching

Unit Network

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Chargin

g ExchangerI/O

Exch

SWITCHING

NETWORK



4.5 OC:

This unit provides the interface to the operation and maintenance center. The monitoring

unit handles the transfer of messages between the operation and maintenance

centre(OMC) and the units of the exchange.

FUNCTION:

• The OC is receiving operation maintenance and positioning message from the

OMC for transmission to the exchange units.

• Transmitting to the OMC operation hardware and software fault message from

exchange units.

• Receiving from the OMC messages intended for the test modules and transmission

return message.

OTHER E-10 EXCHANGES:

All Units PCM

4.6 DSF:

The DSF is working when the event of failure of the OMC or interruption of the link

between the OMC and the monitoring unit the stand by charge recording equipment

(DSF) in the exchange provides the following function:

FUNCTION:

• It records traffic observation and charging messages on to magnetic tape.

• It reinitialisation the memory files of the various exchange units.

Magnetic tape

All Control

Unit

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OC

Exchanger MTU Access

Module



4.7 OPERATION AND MAINTENANCE CENTER (OMC):

The operation and maintenance center handles system supervision. The center provide

with a no dedicated general-purpose Mitra minicomputer. Peripheral are provided for data

storage (magnetic tape and disk) and man/machine dialogue (high-speed printers, VDU

consoles, teleprinters).

Each OMC can handle up to 100,000 subscribers, distributes over a number of exchanges.

The connection to each exchange is provide by a time-slot in one of the network PCM

links: The data rate is therefore 64 KBit/s.

BASIC CONFIGURATION OF OMC:

It comprises the following components:

1. CPU

2. Main Memory

3. Disks UD-50 or UD-80

4. Magnetic Tap Units

5. High Speed Printers (UDU)

FUNCTION:

The functions of a telephone switching system may be divided into two categories:

Control and switching functions;

Exchange management functions;

The management function are concerned with:

• Operation of the translator memories and subscriber accounts.

• Exchange supervision for detection of permanent glow conditions subscriber and

trunk circuit test and loads and traffic observation.

• Exchange maintenance unit positioning and fault location(LOCAVAR).

.

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4.8 FACILITIES IN E-10 B EXCHANGE:

The facilities to the subscriber are managed in the exchanger are managed in the

exchange in two ways :

1. According to the type of line

2. According to the category allocated to the line

Facilities according to type of line:

1. Outgoing only line

2. Incoming only line

3. Bared access

4. Home meter facility

Facilities according allocated to the line:

1. Short code dialing

2. Call transfer service

3. Automatic wake up facility

4. Call waiting facility

5. Hot line facility

6. Conference call facility

7. Subscriber controlled SSTD facility

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CHAPTER 5 : OCB

All new technology switching systems are based on Stored Program Control

concept. The call processing programmes are distributed over different control

organs of the system and are stored in ROM / RAM of different control units.

Processor in the control units by using the programme and data stored in unit ROM

/ RAM process and handle calls. Handling or processing call means to ultimately

establish a connection in a switch between i/c and o/g ends. Depending on the name

and architecture of control units and switch may change but criterion for switching

remains more or less the same.

OVERVIEW OF OCB

5.1 INTRODUCTION:-

OCB-285 is digital switching system which supports a variety of

communication needs like basic telephony, ISDN, etc. This system has been

developed by CIT ALCATEL of France and therefore has many similarities to its

predecessor E-10B (also known as OCB-181 in France).

5.2 SALIENT FEATURES OF THE SY STEM:

1. It is a digital switching with single ‘T’ stage switch. A maximum of 2048

PCM’s can be connected.

2. It supports both analog and digital subscribers.

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3. It supports all the existing signaling systems, like decade, MF (R2), CAS

and also CCITT#7 signaling system.

4. It provides telephony, ISDN, Data communication, cellular radio, and other

value added services.

5. The system has ‘automatic’ recovery feature. When a serious fault occurs in

a control unit, it gives a message to SMM. The SMM puts this unit out of

service, loads the software of this unit in a back up unit and brings it

into service. Diagnostic programmes are run on the faulty unit and the

diagnostics is printed on a terminal.

6. It has a double remoting facility. Subscribers access unit can be placed at a

remote place and connected to the main exchange through PCM

links. Further, line concentrators can also be placed at a remote

location and connected to the CSNL or CSND through PCMs.

7. Various units of OCB 283 system are connected over token rings.

This enables fast exchange of information and avoids complicated links

and wiring between various units.

8. The traffic handling capacity of the system is huge.

9. All the control units are implemented on the same type of hardware. This is

called a station.

10. The system has modular structure. The expansion can be very easily carriedout by adding necessary hardware and software.

11. The SMMs are duplicated with one active other standby. In case of faults,

switch over takes place automatically.

12. The hard disc is very small in size, compact and maintenance free. It has a

very huge memory capacity of 1.2 Giga bytes.

13. The space requirement is very small.

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5.3 SUBSCRIBERS FACILITY PROVIDED BY OCB:-

Facilities to analogue subscribers-

• A line can be made only outgoing or incoming.

• Immediate hot line facility-

• Delayed hot line facility-

When subscriber lifts the handset, dial tone is provided he can dial any number. If

he does not dial a number, within a predetermined time, he is connected to

predetermined number.

• Abbreviated dialing-

The subscriber can record a short code and its corresponding full number in the

memory. Later he dial this number, he has to only dial short code.

• Call forwarding-

When activated, incoming calls to the subscriber gets transferred to the number

mentioned by the subscriber while activating the facility.

• Conference between four subscribers-

Two subscribers while in conversation can include two more subscribers by

pressing button and dialing their numbers.

• Call waiting indication-

When a subscriber is engaged in conversation and if he gets an incoming call,

an indication is given in the form of tone. Hearing this, the subscriber

has option, either to hold the subscriber in conversation and attend the

waiting call or to disconnect this subscriber and attend the waiting call. In

the former case, he can revert back to the earlier subscriber.

• Priority line-

Calls from this line are processed and put through even when the number of free

channels are within a threshold.

• Malicious call identification-

In this category, the number of calling subscriber is printed on the terminal

• Battery reversal- the system extends battery reversal when called subscriber

answers.

• Detailed billing-

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The system provides detailed bills giving details of date, time, etc.

• Absent subscriber service-

When activated, the incoming calls are diverted to absent subscriber service for

suitable instructions or information.

Facilities to digital subscribers:

Digital subscribers are provided all the facilities available to analog

subscribers. In addition, they are provided following facilities which are

called ISDN services. An ISDN subscriber can use many electronic devices

on its telephone line and can utilize them for two or more simultaneous calls of

either

1. Voice

2. Data

3. Video

The ISDN or Digital Subscribers of OCB-283 can be provided the following types

of connections

1. 2B+D LINE :- 2 Voice Channel of 64kbps and 1 Data Channel of 16kbps

2. 30 B+D LINE :- 30 Voice Channel of 64kbps and 1 Data Channel of 64kbps

The following is the list of some of the services to digital subscribers:1. It provides 64kb/s digital connectivity between two subscribers for

data communication.

2. The system provides facsimile services.

3. It provides videotext services.

4. It provides display of calling subscriber number on called subscribers telephone.

5. It also provides the facility for restriction of the display of calling

subscriber number on the called subscriber’s terminal.

6. Charging advice - The system is capable of providing charging advice either in

real time or at the end of the call.

7. User to user signaling - The system permits transfer to mini messages

between calling and called subscribers during call set up and ringing phase.

8. Terminal portability during the call - A subscriber can unplug terminal, carry it

to some other place or room and resume the call within 3 minutes.

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5.4 TIME SWI T CH CONCEPT:-

The time switch comprises of a Speech Buffer Memory, A Control

Memory, An Incoming Highway Of Digital Speech In Parallel Bits and

An Outgoing Highway. This is an Input Associated Controlled Time Switch.

In this switch the Buffer Memory and Control Memory are controlled write

type i.e. the writing in it is controlled. The control function writes in the

control memory at the location corresponding to the Incoming Time Slot

Number, the location where it should be written in the Buffer Memory. Both

these memories are sequential read type. Reading of control memory gives

the address in the Buffer Memory for writing Incoming TS Byte. Thus

reading of Buffer Memory sequentially the TS will be read from the location

given by the Control Memory. Thus a one way Time switching has taken place.

Similarly a both way switching requires two sets of such switches.

5.5 COMMON CHANNEL SIGNALLING NO.7:-

The latest signaling being implemented world wide is now the Common Channel

Signalling. This type of signaling is essential for the setting up of the

ISDN network.

In this type of signalling the signalling information is sent from one

exchange to other exchange in the form of message coded in binary which

is understandable by the intelligent devices available in both exchange. The

CCITT

organization has recommended a standard protocol called CCITT signaling.

The signalling message travels over a single Time Slot of the PCM

connecting the two exchange . This Time Slot is called Common Channel

25



for signalling, hence the name Common Channel Signalling. The message

over this common channel carry all relevant data for any other time slots

circuits which carry voice

or subscriber data. The channels for subscribers are called Voice Channels.

SUBSCRIBER ACCESS UNITS(CSN):-

CSN are so designed that they can be equipped with either analogue or

digital subscriber or both. The cards for analog and digital subscribers

are different, but can be equipped in any slot of the shelf.

CSN can be either placed in the exchange switch room or at a remote location.

Further, subscriber card shelf can also be placed at the rack or at a remote

location. These features provide great flexibility to meet any type of requirement

of dense or sparse connection densities.

SYSTEM APPLICATION S :

1. Local subscribers exchange

2. Remote subscribers unit

3. Transit exchange4. Hybrid local/transit exchange

5. Tandem exchange

6. Centrex(private or public)

5.6 GENERAL ARCHITECTURE OF DIGITAL SWITCHING SYSTEM:

A digital switching system uses the S.P.C. concept and a digital switch. A

brief description of the components is given below:

1. Subs. Access Interface:

Analogue or digital subscribers make entry to the exchange at this interface.

Isdn protocol translation is done at this interface. no. of digital links are

extended from this interface to switch.

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2. PCM Interface:

Any digital exchange can only accept intelligence in pcm decoded form

and hence trunks from other exchange or links from remote subscriber units

or other access systems.

3. Auxiliary Interface:

It is a service peripheral which take care of one or more functions.

4. Controllers:

Various controllers are required to control switching based on the

digital information received from subscribers or over the trunks. the main

control functions are:

• Call Handl e r(Regi s te r ):- this is the control function which processes a call right

from the point of seizure to called party connection.

• Translato r :- this control function basically maintains all data base of subs.

and trunks and provides necessary information to call handler enabling the

same to establish connection between calling linkst/s to called link t/s.

• Charger:- computation of charge based on set principles is carried out by

this control function.

5.7 FUNCTIONAL ARCHITECTU R E OF OCB-285 SWITCH:

The main functional blocks of a ocb-285 switch are:

• Subscriber access sub system which carries out connection of different types

of analogue and digital subscriber.

• “Connection and control” sub system which carries out connections and

processing of calls including pcm connections.

• Operation and mtce.sub function which does the management of database and

helps in carrying out various maintenance procedures in built in the systems.

27



5.8 HARDWARE ARCHITECTURE:

CONTROL FUNCTIONS-CONCEPT OF STATION

For all control function ocb uses concept of a station. Following type of

stations are available:

1. SMT - Trunk Multiprocessor Station

2. SMA - Auxiliary Multiprocessor Station

3. SMX - Switch Multiprocessor Station

4. SMC - Command Or Control Multiprocessor Station

5. SMM - Maintenance Multiprocessor Station

6. STS - Synchronization And Time Base Station

1. SMT-Trunk Multiprocessors Station

It is also known as PCM trunk control station. The smt is a interface for

PCM’s coming from the particular exchange and the remaining world. The

current version of SMT being supplied to India is SMT 2G.

in each SMT 2G, there are 8 modules and in each module there are 16

PCMs. Thus there are 128 PCMs, in a single SMT 2G. SMT 2G is built

around microprocessor 68030.

• Function of SMT-

-Provides terminations of a maximum of 128 pcm’s from trunks

-Carrying out URM

-Transforming the intelligence in PCM to LR for switching to destinations

and transforming the switched LR time slotinto PCM.

2. SMA-Auxiliary Multiprocessor Station

• Function of SMA-

-Tone generation(GT)

Tone generators generate various tones required to be connected during

call processing. These tones are Dial tone, Busy tone, Ring back tone, Processing

tone etc.

-Conference call(CCF)

The conference circuits are used to set up connection between a

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maximum of 4 subscribers. These 4 subscribers can hold conference on the

telephone i.e. they can talk to each other.

Frequency Generation and Reception for R2 MF signalling or for receiving

DTMF frequencies(RGF)

The frequency receivers/generators recognizes the digits dialed through DTMF

instrument and also the MF(R2) signaling and testing etc.

3. SMX-Switching Multiprocessor Station

A SMX is one module of the entire switch matrix system with independent

control. The station is responsible for carrying out connection of an incoming

LR time slot to an outgoing LR time slot.

Switching may effect connection between subscribers, subscriber to

junction, junction to junction subs. To tone or rf, junction to tone or rf etc or

there may be a semi permanent connection for certain data link.

Besides the connection function, the SMX performs following other functions:-

-clock reception from STS & distribution

-fault and alarm processing

-defence of the station etc.

The SMX is connected on 4Mbps links to units like SMT, SMA referred to

as peripherals. Also connected to control units over MAS token rings which provide particulars of connections to be effected.

The network synchronized clock from STS is supplied to SMX. Switching

is done on the strobe of clock and also this clock is supplied to the

service peripherals-SMT, SMA on LR links.

4. SMC—Main Control Station

All the control functions are supported in SMC and one or more of these

functions can be used during call processing. The main control functions

are MR,TR,TX,MQ etc. Relative position of SMC in OCB exchange as shown in

fig. Control functions in SMC communicate on MIS while other communicate

with SMC on MAS. There are 6 common control functions in OCB-283. The

following list illustrates their minimum and maximum numbers.

Number of SMC’s depends on the capacity of exchange. There can be minimum

29



2 SMCs required and maximum number of SMC can be 32. Hardware of all SMC’s

is same but their software is different as per requirement. Types of software used

are:

MQ-marker

MR-multiregister, call analyzer

TR –translator

TX-charging unit

5. SMM-Maintenance Multiprocessor Station

The smm provides the facility for carrying out operation and maintenance

of OCB units and also manage the data base. It carries out following functions:-

-database management and storage

-central defense of the OCB system

-supervisor of token rings

-processing of various commands

-general initialization of the exchange

It provides local link for data processing devices and administration terminals.

This can also be connected to a network management system. It is accessibleto exchange units on one side and to the peripherals on the other side. The SMM also

have access to mass storage devices.

It consists of two units –one act as pilot and other as a standby. Both systems share

a common communication bus supporting various communication peripherals. The

two subsystems are referred as SMMA and SMMB.

6. STS-Synchronization And Time base Station

This is clock system of OCB-283 system which happens to be the most vital unit of

any digital switching system as switching takes place at the strobe of clock

30



PCM

a common clock at every switching station. The clock system in OCB-283,

therefore consists of two parts-synchronization part and time base generator part.

The synchronization interface carries out following functions:-

-Receives max 4 clock inputs from PCM’s coming from other exchange

-In the event of a error detected on the chosen PCM it shifts to other PCM and gives

alarm concerning the faulty PCM

-It maintains reasonably high quality of clock in terms of precision of frequency.

-Counteracts losses of all synchronization links by very high stability oscillator.

-In the event of loss of PCM synch. Runs on free run mode

Re

m

ot

e

Switching

CSNL

CSNL

Matrix

C

S

N

D

S S

31



RING Junctions

MISRING

SMC

Control units

(S

MC

)

SMC

Operati

on

&

mis

c.

unit

(S

M

M

A

&

B)

NMC

GENER A L ARCHITECTUREOF OCB-285

32



CHAPTER 6: MAIN DESTRIBUTION FRAME

6.1 INTRODUCTION :

MDF(main distribution frame) is section,which connect exchange end to

subscriber end. Here the line side (subscribe end ) pair cable terminating at one side of

tag block and the exchange side pair cable terminating at other side. Now both are

connected with jumper pair cable. Jumper pair cables provide more flexibility to

connection and make easy operation of testing the line.

FUNCTION:

The main function of MDF section is to exchange end to line side and to test the

line i.e. subscriber to MDF.it also disconnects the line if any small ac or high dc voltage

passing through the lines, which damage the subscriber, card at exchange end.

MAIN PARTS:

Exchange side tag block, line side tag block, jumpers, fuses.Exchange side tag

blocks make connection of exchange end to jumper and line side modules makes

connection of jumpers to line side. Each tag block provides 100 subscriber pair

connection there are three types of tag block in this section according to types of fuse is

used.

6.2 VACUUM GLASS TAG BLOCK:

In this type, the vacuum glass fuse is used .It connects either exchange side to

jumper or jumper to line side .if any high dc passes through this fuse it disconnect the

line. In present, use of this type of tag blocks decrease due to it complexity to install and

whenever we want to take test either from exchange to MDF or MDF to line side then

we open this fuse and make the wiring compliable.



6.3 T-FUSE TAG BLOCK:

In this type of tag block, the T type fuse is used. it called a T fuse because it just

like T shape in this fuse capacitor is provided which block the ac voltage from the

supply and disconnect if high dc flow through the line. In this tag block 20 rows each

connect5-subscriber line so 100-subscriber line will be satisfied.

• KNOWN TAG BLOCK :

This is very latest version now a days and widely used in connection of exchange to

line because of its simplicity in connection and make test center of the line is very easy

and simple. In this tag block 10 rows each connect 10 subscriber line so 100 subscriber

will be satisfied Between each row a small slot is provided for the testing the line.

6.4 TESTING THE LINE:

At present .two types of testing processor are applied for to test and remove fault from

the line.

(A) Manually

(B) Interactive voice response system

MANUALLY TESTING:

In this system manually test the line.In MDF section ,one coupler is there to

connect either subscriber line to testing.machine to exchange end. In this coupler two

metal plate separated by insulator like plastic. One of the plates, which are connected to

testing machine and other one, is subscriber line . If we take test of subscriber line

otherwise connected to exchange end to take test from MDF to exchange end.

If deflection in testing machine indicate full deflection then we assume that the

line is “OK”, otherwise line is faulty. The lineman does the fault detection and repairing.



Interactive voice response system(IVRS):

In this system, the testing of line is done by the one automatic system, which

called IVRS .It consist of computer, network cad ROM drive, IVRS channel subsystem,

multiple serial card 8 channels etc.

The flowchart in based on IVRS is working. It also provides some other facility

to subscriber, which indicate below.

6.5 CHANGE NUMBER ANNOUNCE REMINDER:

This system is provided to give new or chanced number to the caller when the old

number is dialed. After getting the telephone number from the subscriber, the system

finds the number then it announces the new number.

If the number is not present in changed number in list then the system will announce

that the number is not changed.

E1 or junction interface system will finds the dialed digits and announces the new

number to the caller and in addition to the new number.



CHAPTER 7 : INVERTER:

7.1 INTRODUCTION:

Sinewave weighted high frequency Pulse Width Modulation (HF-PWM)

technique is used for conversion of DC power supply to AC output (Pure Sine Wave).

The PWM wave is composed of a series of pulse of variable width. These pulse

are very narrower at the beginning of the halfcycle & become progressively narrower

towards the end of the next half cycle

DC I/P

O/P TO THE LOAD

The duration of the pulses decides the instantaneous amplitude of the modulating

sine signal with the result that the average value of the output at any given time

approximate to a sine wave.

The higher order harmonics are eliminated with the use of PWM techniques &

they reduce losses in the filter & improve overall efficiency.The PWM technique also

improves the transient response & the reliability of the system. For inverter operation,

high Power Switching MOSFET’S are used.

PRIMARY

INVERTER

SECONDAY

INVERTER

STATIC BY PASSSWITCH



They are rugged devices with square safe operating areas & high peak current

handling capability & also have positive temperature coefficients of current. So they are

easy to parallalise. The inverter semiconductor components are protected by providing

fast protective fuses & snubber circuits.

FUNCTION:

The inverter is intended for the use at different application like computer

Telephone exchange for the supply of AC power to the communication equipment such

as VISUAL DISPLAY UNIT (VDU) & PRINTERS.

These in verters accept dc input & deliver AC output .the dc input to the inverter

can be provided from the charger, with a Battery Floated across at output of the charger.

The charger can normally work as float rectifier but should be able to work as

charger and boost charger and battery require charge.The inverter is connected in Hot

Stand by mode

Normally the primary inverters feeds to the load and other one is on stand by.If

the primary inverter fails the load is transferred to the stand by inverter

automatically.Once the faulty inverter is rectified and switched on the load gets

transferred to primary inverter automatically.

7.2 INVERTER POWER SECTION:

The point marked +ve & -ve is the DC input to the unit.The DC input on/off

switch. Switch is in series with the input so as to facilitate switching on & off of DC

supply to the inverter. DC input fuse is provided to protect the system from any

accidental over current.



The DC supply is given to the bridge network consisting of Power MOSFET

banks & the inverter Transformer T1. Driver card gives the gate drive to the MOSFET

bank in accordance with the signals coming from the inverter and annunciation card.

The control waveform on card is achieved by comparing a sine waveform of a

variable amplitude of particular frequency with a triangular wave of fixed amplitude

with much higher frequency. The comparator gives out a pulse of varying width are

generated & these are coupled to the switching elements.

The output of Inverter Bridge is connected to the double wound inverter

transformer T1. A capacitor connected across the secondary of the output transformer

removes unwanted higher harmonics from the inverter output to obtain allow distortion

sine waveform.

The higher order harmonics are eliminated with the usage of High Frequency

Pulse Width Modulation technique. (HF PWM).

The control circuits of inverter are consists of following cards:

1.INVERTER AND ANNUNCIATION CARD

2.DRIVER CARD

3.DC-AC CONVERTER CARD.

7.21 INVERTER CONTROL CARD:

This card having five major section:

1.Square Wave Generator

2.Control Section

3.Current Feedback Section

4.Voltage Feedback Section

5. Annunciation Section



The first section is generated the main clock required for the control section of

102.4 kHz pulse train.The control section also receives signals from voltage feedback

section which consists of a feedback rectifier & comparator & current feedback section.

The control section will be monitoring all these signals to it & compared with the

programmed values.for any change in parameters, the control section will take corrective

measure on its own by varying the pulse width & keep the output voltage constant.

The current Transformer is used to sense the current at the output of the inverter.

The signal is processed then fed to the feedback section comparator. Here the load

current will be sensed & given respective signal to the control section for corrective

measure.

The voltage feedback section is alsogetting the signal from the feedback transformer.

This section monitors the output voltage of the system continuously, whenever there is

change in the output voltage this section will be give the respective signal to the control

section.

7.4 DRIVER CARD:

Driver card gives the gate driving signal to the switching elements (Power

MOSFET ) as per commands coming from the inverter and annunciation card.



7.4 DC-AC CONVERTER CARD:

The input for this card is taken from same DC supply given as input to the inverter.

These card facilities to generate control supply (+/- 5V) for Inverter and Ann card &

Driver card and four isolated supplies of +/- 15V for Driver card.

If any inverter is fails the load is transferred to other secondary inverter

automatically.

DC I/P

AC O/P

MAIN PCB

POWER

DEVICE

POWER

TRANS-

FORMER

DRIVER

CARD

STATIC

SWITCH

FIRINGCIRCUIT

FILTER

CIRCUT

WAVE-

FORM

GENERA-TOR

VOLTAGE

FEEDBACK CIRCUIT

CONTROL

CIRCUIT

CURRENT

FEED

BACK

CIRCUIT

ANNUN

CIATION

CIRCUIT

POWER

SUPPLY

CIRCUIT



Specification: 1 KVA 2 KVA 3 KVA

Input voltage range 42 to 57Vdc 42 to 57Vdc 42 to 57Vdc

Output voltage range 207 to 230v 207 to 230v 207 to 230v

AC AC AC

O/P voltage

Regulation Against

I/p voltage variation +/-2% of +/-2% of +/-2% of

From 42 to 57 v DC the set value the set value the set valueLoad current variation

From 0 to 100 %(Full Load)

Load Power Factor

Variation from 0.8Lagging to 0.8 leading

O/P Current 4.34 A 4.34 A 4.34 A

O/P Frequency 50 Hz 50 Hz 50 Hz

O/P Waveform Sine wave Sine wave Sine wave

Efficiency Not less Not less Not less

Than 85% Than 85% Than 85%

Power Factor 0.8 Lagging 0.8 Lagging 0.8 Lagging

Unity 0.8 Unity 0.8 Unity 0.8Leading Leading Leading



7.5 VRLA BATTERIES:

Maintenance Free ‘Valve Regulated Lead Acid’ (VRLA) batteries are supplied

from the factory filled with acid and fully charged. They require no toping up. They are

compact, easily transportable and can be used in any orientation without leakage or

spillage of electrolyte. Normally, they do not emit any corrosive fumes or gases. When

the internal pressure increases abnormally the safety valve opens to release gas from the

cell to restore the normal pressure.

In a conventional flooded battery towards the end of the charge, the process of

electrolyzing the water in the electrodes generating oxygen at the positive plate and

hydrogen at the negative plate dissipates major part of the energy supplied by charging.

These gases are lost in flooded system through the vent holes causing steady depletion of

water, necessitating periodic topping up.

In a VRLA system the design is such that the negative plate are fully charged

even when the positive plate is fully charged. Hence almost no hydrogen gas is

generated from the negative plate although oxygen is generated from the positive plate.This oxygen gas generated at the positive plate migrates towards the negative plate and

reacts with the freshly formed spongy-formed spongy lead and turns into lead monoxide.

The load monoxide in turn reacts with sulfuric acid to turn into lead suphate

causing a partial discharge in the negative plate. Thus the negative plate absorbs the

oxygen evolved at the positive plate without being released to the outside. The negative

plate being always in a state of partial discharge never generates hydrogen. This

completely prevents the loss of water.



Voltage:

VRLA cells are 2v units which are assembled in modular racks to get 2V, 4V, 6V,8V

and 12V modules. These racks are mounted horizontally and can be stacked one above

the other.the recommended float voltage is 2.23 Volts per cell. VRLA cells are normally

rated to an end cell voltage of 1.75 Volts per cell.

Chargers:

VRLA cell should be charged with constant potential chargers.The charging

current should be limited to maximum of 0.2ah capacity.The float charging is at

2.23VPC and the recommended boost charge voltage is 2.30 VPC.

SMPS:

Switch Mode Power Supply (SMPS) which was a breakthrough in the field of

power supplies.compared toconventional power supplies. SMPS has a lot of advantagessuch as its small size, easy maintenance less fault and the high power handling capacity.

Development of MOSFET in high power applications was the basic reason behind SMP

power plants.

Basic Principle:

SMPS power plant works on the basic principle of Pulse Width Modulation

(PWM). Incoming AC supply is directly converted to DC supply through a bridge

rectifier . This DC supply is again inverted to a high frequency voltage of 22-35Hz.By

using a transformer , the high frequency voltage is brought down to the required level,

which is then again rectifier.



This rectifier voltage is subsequently filtered in the output filter.The output is

constantly monitored by using a monitaring circuit and provides a rapid feed back to

the single stage inverter for regulating the output. The function diagram is as shown in

fig. below

RECTIFIER INVERTER TRANSFORMER RECTIFIER FILTER

AC O/P

I/ P DC

PE

FEEDBACK CCT

Specification:

Input voltage:

320V to 480V rms. three phase(Nominal Volatage-400V).

Frequency://

45Hz…65Hz.

Out put voltage:

Nominal Voltage : -54.0 +/-0.5V

Adjustment range : -48.0 to –56.0V

In charge mode : -55.2 V(Max)



Rated current:

100 Amps.

Psophometric noise:

Less than 4 mV without battery floated.

Less than 2 mV with battery floated.

Input power factor:

Greater than 0.98 with 50% to 100% load at nominal input.

Efficiency :

Greater than 90% at full Load and nominal input.

ADVANTAGES:

Short circuit protection.

Input over / under voltage protection.

Output over voltage protection.

Constant current features settable from 50 Amps to 100 Amps in auto float/charge

mode.

Constant current features settable from 25 Amps to 50 Amps in boost mode.



7.6 SMPS RECTIFIER:

Introduction:

The SMPS 48V – 5600W is a tree-phase unity power factor power supply with a

wide input voltage range of 3 *185 Vac (with neutral wire) and with a useful output

power of 5600 W delivered to the load. This unit has been developed for cost effective

but highly intelligent modular telecommunication power systems.

Primary application of the rectifiers SMPS 45V – 5600 W are in the supply of

Telecom Equipment where it can provide temperature dependent charging of back – up

batteries using power systemcontrollers.

The convection-cooled unit may be operated up to 60(Cel) ambient air

temperature. The rectifier operated from a nominal 3*230 Vac rms. (with neutral wire)

source. The main frequency may vary from 45 Hz to 65Hz.total harmonic distortion

(THD) of the input current wave from is below 5%.

The output of the rectifier conforms to the generic requirements of

telecommunication power supplies in terms of noise, voltage programmability, as well as

over voltage, overload and short-circuit protecion.the rectifier SMPS 48V-5600W can be

set in the 2 modes ‘auto float’ and ‘auto charge’ by the power system controller.



BIBLIOGRAPHY :

www.bsnl.com

www.ericsson.com

Active Library Explorer (ALEX)

Ericsson system manuals

www.gsmworld.com

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