G.L. Bajaj Institute of Technology & Management

Computer Science & Engineering Department

(Session: 2012-13) Industrial Training Report

On BSNL_____________________

Submitted by:

PRAMOD KUMAR MAURYA

0919210069

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CS 4th year

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ACKNOWLEDGEMENT

It is a pleasure to acknowledge many people who knowingly and

unwittingly helped us, to complete our training . First of all let us thank

God for all the blessings, which carried us through all these years.

We extend our utmost gratitude to Mr. Atul Jain J.T.O who has always

stood by our side and guided, appreciated and encouraged us to get

into more and more ventures. Continuing the same, he enlightened us

in the various stages during the training and provided us with many

insights and useful examples, which proved to be of immense help in

successful completion of this course.

Name- Pramod Kumar Maurya

. Roll.no-0919210069

INDUSTRY PROFILE

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NDUSTRY PROFILE The telecom industry is one of the meteoric growing industries in India. India has nearly 200 million earpiece lines making it the third largest in the world after China and USA. With a growth rate of 45%, Indian telecom industry has the highest growth rate in the world. fib of Indian Telecommunications started in 1851 when the original operational land lines were position by the government near Calcutta (seat of British power). Telephone function were introduced in India in 1881. In 1883 telephone helps were coordinated with the postal system. Indian Radio Telegraph Company (IRT) was make in 1923. After independence in 1947, all the unlike telecommunication companies were nationalized to form the Posts, Telephone and Telegraph (PTT), a monopoly electric discharge by the governments Ministry of Communications. Telecom sector was considered as a strategic profit and the government considered it best to bring chthonic states control. The first wind of reforms in telecommunications sector began to tend in 1980s when the private sector was allowed in telecommunications equipment manufacturing. In 1985, Department of Telecommunications (DOT) was established.

It was an exclusive provider of domestic and long- distance service that would be its own regulator (separate from the postal system). In 1986, two wholly government-owned companies were created: the Videsh Sanchar Nigam Limited (VSNL) for international telecommunications and Mahanagar Telephone Nigam Limited (MTNL) for service in metropolitan areas. In 1990s, telecommunications sector benefited from the general commencement up of the economy.

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ContentsTopics Page No.

INTRODUCTION………………………………….…………………………………….6 E-10B exchange OCB exchange 5ESS exchange

TELEPHONE EXCHANGE……………………………………………………………7 Manual Exchange

Automatic Exchange

TELEPHONE INSTRUMENT…….………………..….…………………..…………8Rotatory Dial TypeElectronic Push Button Type

TELEPHONING SYSTEM……………….……….…………………………………...9

POWER PLANT ……………………………………………………………………….14Float RectifierBattery ChargerSwitching Cubical

FLOAT SYSTEM………………………………………………………………………15

OPTICAL COMMUNICATION…………………………………….…………….....16

ADVANTAGE OF OPTICAL FIBRE………………………………..………………17

MICROPROCESSOR………………………………………..……………………….18

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

ELECTRONIC EXCHANGE FACILITIES…………..………..…………………..19Facilities to SubscriberFacilities to AdministrationVersatilityFacilities to maintenance PersonalI.D.N.I.S.D.N.

CONTROL SYSTEM………………………………………………..…………………22

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ELECTRONIC EXCHANGE…………………………………………………………24Types of electronic exchange

Function of an electronic exchange

TYPES OF SWITCHING SYSTEM………………………………………………….28Time division switching systemSpace division switching system

SWITCHING PROCESSOR….……..……………………………………………….28

SWITCHING PERIPHERALS….………………………………………………….…29

LINE INTERFACE…………..………………………………………………………..30Analog Subscribers line interfaceTransmisssion interface Signalling interface

SIGNALING……………..……………………………………………………………..31Channel associated signallingCommon channel signalling

BASIC MODULES…….………………………………………………………………33

CENTRE FOR DEVELOPMENT OF TELEMATICS ……………………………35

CONCLUSION…………………………………………………………………………37

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 into sounds.

Electronic exchanges play major role in this system. It’s a workplace that serves telecommunication facilities where lines from telephones can be connected together to permit communication. The switching center that houses the terminating and switching equipment is called TELEPHONE EXCHANGE. Following are the types of exchanges where upon we have done training and prepared this report:

1) E10B - This was the first ever fully electronic exchange of our country established in 1990. This name stands for Electronic-10,000 subscribers’ capacity- B (series code). It had given first ever speeded dialing feature in telephony.

2) OCB - This name stands for Optical-Cable-B (series code). It was established in India in 1997. And it had first ever introduced concepts of mobile exchange, call tracing, caller ID, ISDN etc. in our country along with significantly increasing the number of connected subscribers per exchange.

3) 5ESS - This name stands for 50,000 subscribers’ limit- Electronic-Sub-Subscribers. It had implemented concept of sub-subscribers to increase the subscribers’ limits.

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TELEPHONE EXCHANGE

The switching center that houses the terminating and switching equipment is called TELEPHONE EXCHANGE.

TELEPHONE EXCHANGE

Manual exchange Automatic exchange

Cordless Cord Type Strowger Crossbar Electronic (PBX Board) magneto switch CB switchboard

Analog DigitalFig 1: Types of Telephone exchanges

Manual Exchange - Manually operated by a attendant called telephone operator.

Automatic Exchange -Operated by automatic switching equipment.

Local Battery System -Battery bar locally provided with the subscribess for energising the transmitter of their telephone for speech service.

Magneto Switch -Ringing was done by a hand generator producing 17 cps at 75v Magneto type subscriber telephone instrument is used with this system which has a hand -Generator set within it.

Central Battery -Battery was provided centrally at exchange and it provided energy to all the telephone connected to the exchange.

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TELEPHONE INSTRUMENT

Telephone instruments are mainly of three types –1 Magneto Telephone Instrument2 C.B. Telephone Instrument3 Automatic Telephone Instrument

AUTOMATIC TELEPHONE INSTRUMENT

Rotary Dial Type Electronic Push button Type IPT677 Type is allowed for Electronic Exchange

D.T.M.F. Decadic

Fig 2: Telephone Instruments

Rotary Dial Telephone - It comprises three type of circuit (Fig)

1. Dialing Circuit – Impulse spring produces make break pulses. Dial of normal (DON springs are also provided).

2. Ringing Circuit – In ringing circuit 1.8 Micro Farad condensor allows only A.C. ringing current and does not allow D.C. to flow throw it and thus save energy.

3. Speech Circuit – Transmitters converts acoustical energy into electrical energy and receiver converts electrical energy into acoustical energy.

Push Button Type – In decadic dialing make break pulses are generated and in dual tone multi-frequency (DTMF) is generated by mixing of two frequencies from two sets of frequency one set of lower and other set of higher frequency (fig-2).

Difference between DTMF & Decadic Dialing

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Decadic Dialing DTMF Dialing

Make break pulse dialing Store dialing. Dialing speed slow 0.8

digits per second. Different digits take

different times in dialing.

Frequency dialing. Instantaneous dialing. Dialing is faster, 7digits

per second. Same time is consumed in

dialing any digit.

TELEPHONING SYSTEM

Telephonic System can be divided into two parts (fig-3)

1 Internal – Exchange side equipment fall in this category such as –

Main Distribution Frame (MDF) Switching Equipment Power Plant Carrier Station and Microwave station.

2 External – it comprises equipments from MDF to rosselt of telephone such as – (a) U/G Cable Section: MDF to Distribution point box.(b) O/H Line Section: Distribution point to Subscribes window.(c) Internal Wiring: Subscribes window to rosselt of telephone.

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Primary Cables - From main Distribution Frame to cabinet the underground cables are called Primary Cables. It has 600, 800, 1000, 1400 pairs.

D.P.

O/H

CABINET PILLER SUBS WINDOW IIIII

U/G ROSSETT

Fig 3: TELEPHONING SYSTEM

SWITCHING EQUIPMENT

ANALOG SWITCHING- the term analog switching is used as a synonym for space division switching. A path in an analog switching system consists of number of path elements called links, which are interconnected by cross points.

CROSS POINTS- It is a miniaturized switch, which is used to connect various links of speech path. It has two stable states- Closed connecting (0.1 to 200 ohms) Open blocking (10 to 25 mega ohms)

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SW R O O m

MDF

ABBREVIATIONS USED IN TELEPHONE EXCHANGE

PCM Pulse code modulationSSTD Subscriber’s trunk dialing OTD Operators trunk dialingISD International subscriber’s dialingFAX Facsimile auto XeroxTAX Trunk auto exchangePCO Public call officeIDN Integrated digital networkISDN Integrated service digital networkCBNM Central battery non multipleCBM Central battery multiplePABX Private auto branch exchangePBX Private branch exchangePMBX Private Manual Branch ExchangeEPABX Electronic Private Auto Branch Exchange ALU Arithmetic Logic Unit LDCA Long Distance Charging AreaSDCA Short Distance Charging Area CDOT Center for Development of Telematics LAN Local Area NetworkWAN Wide Area NetworkE-MAIL Electronic MailI-NET Computer Network within LandINTERNET International Computer NetworkTELEX Telegraphic ExchangeCTO Center Telegraph OfficeDTO District Telegraph OfficeSPC Stored Programme ControlDTMF Dual Tone Multi FrequencyRAX Rural Auto Exchange

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Fig 4: Various types of cross points

Various types of cross points have been evolved, but sealed contact type reed relays are commonly used in analog switching networks. Memories are preferred. A basic switching stage consists of reed relay arranged in a row and columns in the form of a matrix. Several such stages connected in tandem constitute a switching network. There are two types of switching network viz. Unidirectional and bi-directional. Transit exchanges are unidirectional network. Whereas the subscriber local exchange are bi-directional networks.

DIGITAL SWITCHING: Digital switching has become a synonym for time division multiplex. In digital switching system, digital

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CROSS POINT

ELECTRO MECHANICAL ELECTRONIC

CROSSBARDERIVATIVESWITCHES

SEALEDSWITCHES BIPOLAR

FIELD EFFECT

REED RELAY

OTHERS THYR TRANSISTOR FET MOS CMOS

ELECTRICALLY LATCHEDMAGNETI

signals are switched in two nodes, time switching and space switching. Time switching basically involves rearrangement of channel sequence in the same PCM from whereas space switching involves interconnection of same channels of a different PCM high way. In a practical digital switching both time and space switching stage is employed to increase the traffic handling capacity of the switch at minimum cost. Among the various possible combinations TST structure is most commonly used. Synchronization of various exchange clocks in a digital network is essential to provide required services. Causing a slip due to mismatch between the clocks will result in multination of information and description of services. Hence, slip has to be controlled using plesiochronous and synchronous approaches.

MODULATION: Often the message signal is not suitable for transmission over the medium in its original forms. Therefore, the message signal is located in a carrier wave, which is more suited for transmission over the medium. This process is called modulation of the carrier wave. At the receiving end station the message signal received back from the incoming modulated carrier wave by a process is called demodulation which is inverse of modulation.

MULTIPLEXING: Modulation enables multiple message signals to be simultaneously transmitted over the same medium without interfering each other. Transmission of multiple message signals simultaneously over a medium is called multiplexing. Modulation is essentially a process of relocation of a message signal in a carrier wave, which is more suitable for transmission for transmission over the medium than the message signal itself.Three types of modulation can occur-1. Amplitude modulation2. Frequency modulation3. Pulse modulation

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POWER PLANT

One of the primary requirements of any computer system is that service will be available to the subscriber at any time. In the vast majority of exchanges the electrical energy required for signaling, switching, speed transmission mains. The exchange power system is designed to provide continuous and uninterrupted telephone service even when the public electric fails. We can divide power plant in three major blocks such as

FLOAT RECTIFIER

BATTERY CHARGER

SWITCHING CUBICAL FLOAT RECTIFIERS: - It constitutes one item of telephone exchange power plant. The function of float rectifier is to drive power supply A.C. mains and deliver to the telephone exchange equipments continuous and filtered D.C. supply at nominal voltage of 50 volt (actual terminal voltage is 51.5 volt). The voltage of supply is to be maintain with closed limits of +-0.5 volt unvarying impact voltage and output load currents, on set or more batteries are normally floated across the float rectifier in parts are as follows 3-phase step down transfer

Half controlled 3phase bridge rectifier

Filter circuit and controller

BATTERY CHARGER- It is a part of power plant in an exchange and provides initial, refresher and boost charging for the batteries. The 24 lead acid cell battery can be charged from 1.8V per cell to 2.7 volt per cell.A.C. INPUT 350V, 370V, 390V, 410V, 430V+- 10%

50Cps+-2Cps

3-phase 4wire system

D.C. INPUT For 24 cells charging

44volt to 54volt at 150 Ampere

45 volt to 65 volt at 75 Ampere

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COMPONENTS 3-phase step-down main transformer

Ballast chokes

3phase full wave rectifier

SWITCHING CUBICAL: -

It provides facility for

Floating any one or more batteries

Charging any one battery at a time

Supervisory alarms for all associated units

Incorporates auto-paralleling panel, which contains the circuiting for sequential switching i.e., for switching ‘ON’ and ‘OFF’ automatically to suit exchange load one or more float rectifiers whose output are in parallel.In case where exchange load is met directly from the mains, provision is also made for alternate source of supply in the event of mains failure .The emergency energy is derived from

Battery of secondary cells.

A combination of batteries of secondary cells and prime mover generator sets. Secondary cell or accumulators used in department are mostly of bad acid type and hard rubber container

FLOAT SYSTEM: In this system the battery supplies only the emergency reserve requirements of the equipments during mains failure. The battery is always kept connector across the load in the float system in a fully charge state but the operating conditions are so maintained that the floated battery does not discharge in to the load as long as the mains power supply is available. As soon as the mains fail the floated battery takes the load of the each. Thus there is absolutely no break in D.C. power supply when the mains power supply fails.Various forms of standby supply arrangements are available, out of which the engine generator sets are most common. This consists of two separate machine an engine and the other generator or alternator. A generator is an electromagnetic

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machine, which converts natural form of energy to mechanical energy. A diesel engine is an internal combustion engine, which operates on liquid fuel.

OPTICAL COMMUNICATION

Optical fiber is a latest means by which we transmit information (speech, data, video), in the form of light through optical fibers (fig. 5). This communication requires five stages. Information is converted in to electrical signals by encoder. Electrical signals are converted in to optical signal by means of a light source. Optical signals are transmitted to the distant station through optical fiber media. At the distant station optical signal are again converted in to electrical signal by means of detector. The electrical signal is further converted in to information (speech data and video) by means of decoder at the distant station.

Optical fibers have following two parts Core (Internal part) Cladding (Outer periphery)Out surface of cladding creates a difference in refractive index due to which total internal refraction phenomenon happens in central core. Core and cladding made of transparent substance like silica or Borosilicate, but the refractive index of cladding is less than core.

ADVANTAGE OF OPTICAL FIBRE Thousands of circuit can be provided through optical fiber. The cable is less in size and diameter and so easily transportable. Noiseless circuit can be provided through this media There is no risk of fire, electric shock and short-circuiting. There is no effect of excessive temperature on it Repeaters are provided at long intervals and repeater less chain is also possible.

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Fig 5: Organization of typical microcomputer

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MICROPROCESSOR

I/P DEVICE

O/P DEVICE

SEMICONDUCTOR MEMORY

FLOPPY DISKS

C.D. CASSETTS

Microprocessor

A microprocessor is a complex electronic processor on a single silicon chip (Large-scale integrated circuit). It is capable of performing arithmetic and logical functions under the control of program. Functional units of microprocessor-1. Arithmetic and logic unit2. Registers (Temporary memory)3. Timing and control unit

Functions1. FETCH2. DECODE3. EXECUTE

Bus SystemVarious switching peripherals are connected to central processor by means of a common bus system. A bus is a group of wires on which data and command pulses are transmitted between the various sub units of a switching processor and switching peripherals. The device to be activated is addressed by sending its address on address bus. The common bus system avoids costly interconnection among various devices (Fig-6).

Address Bus-The address bus normally consists of 16 lines. To access a particular device or memory location, the microprocessor transmits its address on these lines.Data Bus-The data bus usually has parallel conductors. It is a path for transferring data in and out of the processor.

Address bus is unidirectional and data bus is bi-directional.Control Bus-Control bus is used for transmitting and receiving control signals between microprocessor and various I/O devices.

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Electronic Exchange Facilities

Electronic exchange facilities can be divided in three major groups-1. Facilities to subscribers2. Facilities to Administration3. Facilities to maintenance personal

Facilities To Subscriber- MFC Push Button Dialing ( DTMF dialing) Priority subscriber lines Toll (outgoing call) detraction Service interception Abbreviated dialing Call forwarding Do not disturb Conference call Camp on busy Call waiting Call repetition Third party inquiry Priority of calls to emergency position Subscriber charge indicator Call charge print out or immediate billing Malicious call identification Interception or announcement Connection without dialing Automatic wake-up alarm service Hot line or private wire Denied incoming call Instrument locking Free of charge call Collect call

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Facilities To Administration- Reduced switch room accommodation Faster installation and easy extension Versatility Versatility-1. Adopting various signaling and call charging pattern2. Increase facilities in rating and numbering by simple

commands3. MANAGEMENT FACILITIES: Automatic billing, centralized

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

4. Wide range of subscriber services5. Wide range of dial speed( 5 to 22 digits/ second)6. Easily handling of group line (PBX)7. Unlimited possibilities for line translation, digits storage and

route analysis8. Compatibility with new techniques in signaling an data

switching

Facilities To Maintenance personal- Automatic fault processing (Hardware checking) Automatic changeover to standby unit in case of fault in one

unit Diagnosis Statistical programme Blocking facilities Overloading security

I.D.N (Integrated Digital Network)-I.D.N is a network in which both the transmission media and switches employ digital techniques. This network combines the advantages of both switching and transmission. In this system, speech signals are converted to digital signals at transmitting and receiving stations. This system has easy maintenance and supervision, which is carried through computers. This enables more flexibility in terms of remote controller and subscriber units and reserved in saving of circuit cost.

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I.S.D.N (Integrated service digital network)-Presently, there is a multiplicity of services such as telephoning, telex, data cable television etc. that are provided by separate dedicated network for each of them. These non-integrated services require separate switching system. Special subscribers access plants, individual trunk networks and separate operations and maintenance staff. These services are costly to the subscriber as well as to department. In I.S.D.N, these services are provided by one integrated network, which can be accessed by different customer premises equipment.In I.S.D.N, subscriber loop from the local exchange will be terminated at the network terminal (N.T). From N.T the signal will be distributed to the information sockets. These information sockets will be distributed in the premises just like power sockets are distributed for providing on the information sockets, different terminals for voice and nonvoice services can be connected.

Control System

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A system can perform any work by a single processor or multiprocessor.

Fig 6: Functional Division & Segmenting

Functional Division- each processor does only a certain function exclusively allotted to it for the entire exchange.

Segmenting –each processor carrying out all the functions for a certain segment of the exchange (Fig 7). Redundancy- there is different standby methods available in control structure of electronic telephone exchange.

1. Hot standby redundancy2. N+1 redundancy3. Synchronous replica duplication4. Load sharing (fig 11)

Hot standby redundancy- there is a standby available for all functional units separately. Even anyone or more units fail. The working of exchange will not be affected (fig 8). Processors when Segmenting is used

P1 P2 P3 PN

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Control System

Single Processor System (Monarchic)Multiprocessor System (Distributed Control)(Oligrachic)

One level System Hierarchical System

Functional Division Segmenting 2 Levels 3 Levels

F1 P1’F2 P2’

F3 P3’ Processes

XGE when Function function

division is used

Fn Pn’

Ultimate capacity of XGE

Fig 7: Functional Division & Segmenting

To switching network

Fig 8: Hot Standby

N+1 Redundancy- one unit is extra added in parallel with N units. In the failure of any one unit, this extra unit takes the load of the failed unit, but if two units will fail, the exchange cannot work (fig 9).

Synchronous replica duplication- the standby unit is always connected and compared by a clock pulse. If there is a difference in two units, it means one unit is faulty (fig 10).

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A1 A2 B1 B2 N1 N2

Electronic Exchange

These are entirely computerized and electronic devices, which work on store programme control. Electronic logic component can do ten thousand times operation during signal in the comparison of electromechanical exchange.

In an electronic exchange a single control device simultaneously process a number of calls on time-sharing basis. Such centralization is more economical, but it is disadvantageous in making switching system more vulnerable to system failure. This, however, can be overcome a standby control devices. These electronic exchanges have powerful processing unit. Part of control equipment capacity utilize for function other than for processing. There are two types of electronic exchange.

Analog Exchange- this exchange uses one physical path for one call. Hence, full availability could not be achieved due to internal blocking.

To switching network

CC

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Fig 9: N+1 Redundancy

Clock

Copartor

Fig 10: Synchronous Replica Duplication

Digital exchange- digital switching enables sharing a single path by several calls. Hence, it provides full availability and there is no change of internal blocking.

Function of a electronic exchange The primary purpose of an exchange is to provide a temporary path for simultaneously bi-directional transmission of speech between

1. Subscriber lines connected to the same exchange (local switching)

2. Subscriber lines and trunks to other exchange (outgoing trunk calls)

3. Subscriber lines and trunks from other exchange (incoming trunk call)

4. pairs of trunks towards different exchange (transit switching)

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MA MB

A BC

~

TELEPHONE ENVIRONMENT

These are called the switching function of an exchange and are implemented through the equipment called the switching network. An exchange which can set up the just first three types of connection is called a subscribers of local exchange it is called a transit or random exchange.

Other distinguish function of an exchange1. Exchange of information with the external environment

(subscriber’s line or other exchange) that is signaling.2. Processing and signaling information and controlling the

operation of switching network that is control.3. Changing and billing.

All these function can be provided more efficiently using computer controlled electronic exchange and functional division of a store programme. Control electronic exchange can be given as (fig 11)

Line & Trunk Terminal Equipment

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SwitchingNetwork

DistributorScanner Marker

CommonChannelSignallingterminal

Channel AssociatedSignallingterminal

BUS

Switching processor

Fig 11: Functional Subdivision Of an SPC Exchange

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Central Control---------------- Memories

Man-Machine Dialogue peripheral

1. Terminal equipment - it provides an individual basis for each subscriber’s line and for inter exchange trunk.

2. Switching network - the main function of switching is setting up the temporary connection between two or more exchange termination and transmission of speech and signals between terminations with reliable accuracy.

Types of switching system

There are following two types of switching system in India(a) Space division switching system - in this system a

continuous physical path is being set up between input and output terminations. This path is separated for each connection and is held for the entire duration of the call.

(b) Time division switching system - in this system a number of connections shares the same path on time division sharing basis. The path is not separate for each connection, rather, is shared sequentially for a fraction of time by different path. This process is repeated periodically at a suitable high rate. The repetition rate is 8 KHz in ones every 125 microseconds for transmitting speech on telephone network.

Functional subdivision of an SPC exchange

1. Switching processors consisting mainly of processors and memories.2. Switching peripherals (scanners distributors and marker) are interface circuit between control system terminal equipment and switching network. 3. Signalling interface depending on type of signaling used.4. Data processing peripherals (tele-type writers, printers e.t.c.) for man machine dialogue for operator and maintenance of exchange.

Central Control

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It is a high-speed data processing unit that controls the operation of the switching network (fig 12)

Programme Store- in this, set of instructions called programme are stored. The programmes are interpreted and executed by the central control.

Data Store- it provides for the temporary store of transient data, required in processing calls such as digits dialed by subscribers, busy/idle status of lines and trunks e.t.c. Data Store is temporary memory whereas translation and programmes stores are semi permanent type. The information in semi transparent memory does not change during the processing of call but the information in data store changes the continuously origination and termination of each call.

Switching peripherals The time intervals in which the processor operates is in the order of micro second, while the components in telephone switching system operate in millisecond. The equipment known as switching peripherals is interface between two equipment working at different speeds. The interface equipments act as speed, buffer as well as enables conversion of digital logic signals from the processor to the appropriate electrical signal to operate relay cross points etc scanner, distributor and marker fall under this category of devices.Scanner-its purpose is to detect and inform the central control of all significant events on subscriber lines and trunks connected to the exchange.Marker-it performs physical set up and release of paths through the switching network under the control of central control.Distributor- it is a buffer between high speed, low power central control and relatively slow speed high power signaling terminal circuit.

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Line Interface

To enable an electronic exchange to function to the existing outdoor telephone network certain interfaces are required

1. Analog subscriber line interface2. Transmission interface3. Signaling interface

Analog subscriber line interface- The function of a subscribers line interface for each two-wire line is often known by the acronym “BORSHCT” which is

B- Battery FeedO- Overload ProtectionR- RingingS- Supervision of loop statusH- Hybrid C- CODECT- Connection to test equipment

All these functions cannot be performed directly by electronic circuiting so, suitable interfaces are required.

Transmission Interface- transmission interfaces between analog trunks and digital trunks such as A/d and D/A converters known as CODEC. These may be provided per line and per trunk basis ( on the basis of one per 30 speech channels).

Signalling Interface- A typical telephone network may have various exchange systems (manual, stronger, crossbar and electronic e.t.c.) each having different signaling schemes. In such an environment an exchange must be in accordance with several different signaling codes.

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Signaling

There are four types of signaling possible: - 1. Ring Down Signalling 2. DC signaling 3. E & M signaling4. Digital signaling

Digital Signalling can be performed in two ways: -

Channel Associated Signalling- Initially all signaling between automatic exchanges was decadic i.e. telephone numbers were transmitted as trains of 1 to 10 pulses, each train representing one digit. To increase the speed at which the calls could be set up and to improve the reliability of signaling, compelled sequence multi frequency signaling system was then introduced. In this system each signal transmitted as a combination of two out of a group of say 5 or 6 frequencies. In both decadic and multi frequency systems the signal for each call are sent over a channel directly associated with the inter exchange speech transmission circuit is used for that call. This is termed as channel associated signaling.

Common Channel Signalling- recently a different technique has been developed known as common channel signaling. In this technique all the signaling information for a number of calls is sent over a signaling link independent of the inter-exchange speech circuit. Higher transmission rates can be utilized to enable exchange of much larger amount of information. This results in faster called set up. Introduction of new services i.e. abbreviated dialing and more retrials ultimately accomplish higher call completion rate. Moreover it can provide network management and traffic engineering.

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To switching Network

Fig 12: Central Control

Configuration and is based on 32 channels PCM structure. It uses a basic rate of 64 kilo bit per second and 2 mega bit per second . Primary multiplexing control is distributed over the system by using 16 bit microprocessors. All the critical control circuitry as built in redundancy. System hardware utilized advanced concepts in microelectronics for a compact and optimum design. Basic memory unit has been implemented as 2 mega bit dynamic RAM based with 256 kilo bit as the basic dynamic RAM chip.Single chip digital signal processors are used for implementing DTMF and MF receiver. A high performance, high density VLSI chip detects multiple tones simultaneously performs signal filtering on four channels. This approach reduces costs, power dissipation and saves space on PCM. Analog to digital conversion on the line circuit has been achieved by using a per channel coder decoder (CODEC) chip.

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Central Control Processor

Programme Store

Translation Store

Data Store

BASIC MODULES

1. Base module (Fig 13)2. Central module3. Administrative module4. Input output module

PART OF BASE MODULE

1. Terminal units for interfacing analog lines and trunks and providing special circuit.

2. Digital terminal unit – for interfacing digital trunks.3. Time switching unit - for message switching and provision

of service circuit.4. Base processor unit - for control message, communication

and call processing function.

CARDS IN TERMINAL UNIT

1. Line circuit card.2. Analog trunk card.3. Signalling processor card - scan/drive function origination

detection, answer detection, digital detection analysis transmission and several detection.

4. Terminal interface card.

TIME SWITCH UNIT

It has a time switch for time switching within the base module, a message switch for controlled message communication within the base module and between base module and a service unit for providing call processing support. Like MF/DTMF circuits Answering circuits and tones e.t.c. 128 channel multiplexing circuits and 16 bit microprocessors.

BASE PROCESSOR UNIT 1. C.P.U card.

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2. Base interface controller card (B.I.C).3. Bus interface device (B.I.D).4. Memory unit (M.U).

CENTRAL MODULE

It is responsible for space switching of inter module calls and communication between base module and administrative module.

LINE MODULE BASE MODULE LINE MODULE

Fig 13: Concentration of base module

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T U

T U

T U

T U

T U

T U

T U

T U

T U

T U

B P U

T S U

T U

T U

T U

T U

T U

T U

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SIGNAL PROCESSOR Signaling information as the dialed digits, ring trip, trunk seizure etc is separated at the terminal interfaces and carried to SP on a time-multiplexed link. The SP passes on this information to the T.I.C similarly, T.I.C uses S.P for effective any device in the terminations. E.g. ringing current.

TERMINAL INTERFACE CONTROLLER It drives the identities of the calling and the called terminals and stabilizes a path through the switching network between these terminals. The T.I.C communicates with the R.C.P on the high data link controller (H.D.L.C) link for all call related information.

R.A.X CONTROLLED PROCESSOR (R.C.P.) It is a microprocessor-based processor, which handles the call processing function. R.C.P stands the terminal connection related information to the T.L.C over the H.D.L.C link.

MANTENANCE PANNEL It is connected to R.C.P viz RS232C link for system for operation and maintenance function A DC-to-DC converter generates the various voltages required for the system operation and also provides ringing for the subscriber loop. CDOT RAX uses integrated circuit based on metal oxide silicon, MOS, CMNOS low power schottkey transistor. In, Transistor logic bipolar 10 types of cards are used.

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DATA PROCESSING PERIPHERALS1. Man machine dialog terminal

a. Tele type writerb. Visual display unitc. Printer

2. Special purpose peripherals employed for carried out repeated function such as subscriber line testing which requires high speed.3. High-speed large capacity data storage

a. Magnetic tape driveb. Magnetic disk unit

These are used for loading software in processor memory.

4. Maintenance peripheral-Such as alarm initiator special console are used primarily to indicate that automatic maintenance procedures are failed and manual attention is necessary.

CONCLUSION- The electronic exchange work on the principle of stored program control (SPC). At the call processing are performed on the basis of a pre designed program which is stored in the memory of a central processor. Though the initially designed electronic exchange had single centralized processor, the control is being decentralized providing dedicated microprocessor controlled subsystem for improved efficiency and security of the system. This modular architecture also adds future expansion.

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Requirements

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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 uses Telephone, electronic equipment that converts sound into electrical signals that can be transmitted over distances and then converts received signals back into sounds.

Electronic exchanges play major role in this system. It’s a workplace that serves telecommunication facilities where lines from telephones can be connected together to permit communication. Thus the switching center that houses the terminating and switching equipment is called TELEPHONE EXCHANGE. Following are the types of exchanges where upon we have done training and prepared this report:

1) E10B - 2) OCB - 3) 5ESS -

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