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A Report onOne month vocational Training

At BHEL, Haridwar

A training Report submitted in partialfulfilment of the requirement for the award of

degree of Bachelor of Technology in

“ELECTRONICS & COMMUNICATIONENGINEERING”

Submitted By:Submitted to:Dilip Sipani Mr. Vishal Verma(DGM)Roll No - 08EAREC031

Telecommunication Dept., BHEL, HEEP, HaridwarBranch - ECE

SIR CHOTU RAM INSTITUTE OFENGINEERING

CCS University MEERUT

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CERTIFICATETO WHOM IT MAY CONCERN

This is to certify that Ms. RASHMI PANDEY student of B.Tech,

Electronics and Communication Engineering, ROLL NO. 097041, from “SIR

CHOTU RAM INSTITUTE OF ENGINEERING & TECHNOLOGY,MEERUT” has undergone 4 week industrial training in telecommunicationsystems under the guidance of Mr. Vishal Verma, D.G.M at telecom division of Heavy Electrical Equipment Plant (HEEP), Bharat Heavy Electricals Limited(BHEL), Haridwar from JUNE 11TH 2011 to JULY 9TH , 2011. Her disciplineand performance during the training period was excellent. We wish her a very

prosperous and bright career in future.

Mr. Vishal Verma Mr. V.K JoshiDeputy General Manager Sr. TechnicianWEX – Telecom WEX - TelecomHEEP, BHEL, HEEP,BHEL,Haridwar - 249403 Haridwar– 249403

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ACKNOWLEDGEMENT

First and foremost, I would like to thank my respected parents, who alwaysencouraged me and taught me to think and workout innovatively what soever be the field of life.

I pay my greatest regards to Mr. Vishal Verma (D.G.M. – Telecom), whoprovided me valuable guidance and all technical support, which was veryessential for completion of the training.

I also wish to thanks Mr. V.K Joshi, (Sr. Technician – Telecom) for theirkind and continual support and constructive suggestions given during thecourse of this training. Who helped me a lot in giving minute details of Telecom Department and enlightened me with the knowledge of Exchangeequipment and their working.

Last but not the least I would like to thanks to all the staff of HEEP (BHEL)who devoted their time for me despite their busy schedule.

NAME RASHMI PANDEY

BRANCH Electronics & Communication Engineering INSTITUTE SIR CHOTU RAM INSTITUTE OF ENGINEERING &

TECHNOLOGY, MEERUT

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Contents

1. Introduction to Organisation 5- 7

2. Introduction to Telephonic System 8

3. Telecommunication

4. Electronic exchanges10 - 14

5. Telephone Lines

6. Connection Types 16

8. General faults Occurring in an Exchange17 - 21

9. Special Features for users in various Exchanges22 - 23

10. Optical Fibre System24

11. Maintenance25

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INRODUCTION TOORGANISATION

BHEL – An Overview

Bharat Heavy Electricals limited, BHEL,is the largest engineering andmanufacturing enterprise in India withglobal credentials. Today it ranksamong the leading power Equipmentmanufacturers in the world. Set up in mid-fifties, BHEL has diversified its products

base over the years and today BHEL caters to the need of all key sectors of theeconomy. BHEL‘s products cater to the wide spectrum of customers in various fieldslike power generation & transmission, oil exploration & production, transportation,steel & metals, fertilizers & petrochemicals, refineries, cement plant, heavyengineering industries, non-conventional energysources, defence equipments, etc. More than 65% of the installed capacity forelectrical power in India is contributed by BHEL. The wide network of BHEL‘s 14manufacturing divisions, 8 service centres, 4 power sector regional centres, 18regional offices and over 150 sites spread all over India & abroad enables thecompany to promptly serve its customers & provide them suitable products systems

and services at competitive rates. BHEL manufactures almost all high technologyproducts required for power sectors viz. Steam Turbines, Gas Turbines, Nuclearturbines, Generators, Boilers, Heat Recovery System Generators, Pump &Compressors, Heat Exchangers, and Control Instrumentation etc. BHEL has carriedout ‘System Engineering’ and ‘Turnkey Execution’ of projects involving coal, liquid &gas based power plants not only in India but also in countries like Malta, Cyprus,Malaysia, Saudi Arabia, Oman, Libya etc. BHEL‘s technology for products/systems isat par with the latest/best in the world. BHEL has collaborated with leadingcompanies in world like M/s Siemens, Germany; M/s General Electric, USA; M/sAlstom, France etc.

.Customer Training Programme – A comprehensive training program on theDesign Features, System Philosophy, Operation & Maintenance, troubleshooting etc.of turbo generators is offered to the customer engineers and technicians to impartknowledge. Experienced faculty from concerned disciplines provide the conceptualinputs followed up by shop visits.

Quality & Reliability

Quality is prime concern for BHEL. Turbo generators manufactured by BHEL are

certified ISO: 9001. The certificate is testimonial of BHEL‘s tryst with quality. It isendeavour to achieve excellence in all business processes BHEL has adopted and

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implemented new concepts to ensure compliance to standards/specifications atvarious stages of the project viz. engineering, manufacturing, testing, erection,commissioning etc.

In past few years the field of communication has been developing with no leaps orbounds. It has become a necessity of each human being to be connected with eachother. Telephone is rapidly becoming a tool to quench this thirst.

In Automatic Telephony, operators are not required to establish connectionsmanually between the different calling and the called subscribers as are required inthe case of manual telephone systems. In these system subscribers those selvesestablish required connections by operating the different switches placed at the

central place known as the EXCHANGE from their telephones at remote place from it. The automatic telephone systems are rapidly replacing manual ones due to theiroutstanding merits over the latter types, some of which are enumerated below:

• In Automatic Telephony higher level of secrecy is maintained due to absence of Operators who can overhear the conversation if they like in the manualtelephone Systems. The working of an Automatic Telephone system does notdepend for its

• efficiency on the personal efficiencies of the operators.

• There is no possibility of the calls being missed or wrong metering being done

due to faults of

• The operators or due to phonetic errors between subscribers and the operators.

• As no operator is required, the running cost of the exchange is reduced.

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“ The modulate signals has to be transferred from the transmitter to the receiverthrough a medium and this medium is also called a channel” The channels menaslong transmission path. The various channel available today is cable, radio wave andlight wave

-

Radio system characterstics

When a radio frequency current flows in to a transmitting antenna,power is a radiated in a no. of direction is called an electro-magnetic

wave.The radiated energy will reach the receiving station by one or morefive different mode.

1. Surface wave2. Sky wave3. Space wave4. via a satellite5. Scattering

USAGE :1. World wide communication in LF Band & Broad

casting in MF Band2. Long distance, Radio telephone, sound brodacasting3. Sound and TV broadcasting4. Multi channel telephone system

5. Use in UHF & SHF band to provide Multi channeltelephoniy lines

Modulation of signal :

1.Amplitude modulation2.Frequency modulation3.pulse modulation

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The band width require for the transmission of commercial qualityspeech is 300-3400 Hz .

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Telephone Network, BHEL

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INTRODUCTIN OF ELECTRONIC EXCHANGE:

CommunicationVisualAudio

Generation of Exchange

Two phone instrumentsManual telephone exchangeManual automatic exchangeElectronics exchange

Electronic Exchange

Cross bar exchangeC dot exchangePulse code modulation exchangeDigital exchange

“Any exchange has to section”

• Indoor

Switch roomBattery roomOperator roomM.D.F

• Outdoor

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Switch roomExchange cabinetDifferent PCB cardPRI CARD

TELEPHONE

Inventor - Alexander graham bell

Launch year - 1876

Available - World wide

The telephone (in the Greek language tele means “far” and phonemeans “voice”)

C dot Exchange (max exchange) : It can be configured fromfour basic modules

1. Basic modules2. Central modules3. Administrative modules4. Input – output modules

Electronic Exchanges are of two types:1. Tone type2. Pulse type

1. Tone type: In this type of exchange sine waves are used. Their speed of dialingfor a given number is more than that of Pulse type.

2. Pulse type: In this type of exchange square wave is used due to which thedialing speed is lesser. The telephone apparatus used for both types are different

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in construction. But now days both types of apparatus are integrated in a singlemachine in which switch-over can be made via a selector switch.

TONES USED IN MODERN TELEPHONY

Dial Tone: When handset is picked up from the cradle, then Dial tone is heard if afree line is available. This means that the instrument is ready to send the signals tothe exchange. When the subscriber takes up the receiver then signals are sent M.D.F.then to I.D.F., line Number block and to Peripherals where in various line-cards aremounted in a shelf. When corresponding number on the line-card is free then theRinger section of that Peripheral generates a signal called tone. This tone is acontinuous burble sound of 400 Hz modulated by 25Hz and is sent to the callingsubscriber as soon as his line seizes the free line. The subscriber must not dial before

receiving this tone; otherwise he is liable to get wrong connection. If he does not getthis tone, he should try after some time.

Busy Tone: When the called subscriber is engaged with other call, this tone is heard.It consists of a sound of 400 Hz which is regularly interrupted at equal intervals. It isgenerally on for 0.75 sec and off for also 0.75 sec

Ringing Tone: When a number is dialed then telephone of the called subscriberstarts ringing. Calling subscriber should get this information and this is indicated bysending ringing tone of interrupted 400 Hz supplies modulated by 25 Hz and itsdurations are generally equal to the duration of ringing current, which rings the bell.It may be 0.4 sec on, 0.2 sec off or it may be 0.75 sec on and 0.75 sec off and so on.When this ringing tone is received, the calling subscriber knows that the connectionis completed and that the bell of the called subscriber is ringing.

Number Unobtainable Tone: This tone is sent when the number dialed cannot beobtained. If any subscriber dials which is not actually connected to the exchange, thisindication is send. This is also a tone of 400 Hz with interruption of 200 ms at every 3sec.

Now-a-days push button type telephone apparatus are used. This apparatus can beexploded into following sections:

1. Ringer section2. Speech section (Transmitter and Receiver section)3. Voltage limiter section

From telephone exchange two wires or connectors run for each number, in which oneis neutral and the other is main or positive. For the telephone circuit to work thenecessary supply is provided by the exchange. Like other circuits telephone alsooperates when a circuit is established between calling and called subscriber. Whenone dials a number then the corresponding relays at the exchange established a

circuit automatically. The telephone exchange supplies 40-60 volt DC and 110/20 Hz to operate this circuit. This is required because of voltage drop that may creep in

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long transmission wires. As soon as the handset is picked-up this 48-volt DC supply isavailable at voltage limiter section, dialing pulse generator and speech section.

In telephone dialing two types of frequencies are used which are:

• High band tone (1216 Hz. to 1645 Hz.)

• Low band tone (701 Hz. to 936 Hz.)

Frequencies used in Telephony

The numbers from 1 to 5 falls in low band and 6 to 9, 0 falls in high band. Till thehandset is on-hook, the ringing section of the apparatus is on through telephone linebut on lifting the handset the ringing section becomes off, also the dialing andspeech section becomes ready. On lifting the handset first the dial tone is receivedwhich is amplified by the amplifier of speech section.

When a number is pressed on the keyboard, the dialing pulses are made on and off

according to the number dialed. For example if 5 is pressed then dialing pulses aremade on and off 5 times. This process can be heard on the receiver. There is a gap of 1 sec. between consecutively pressed numbers.

When the handset is placed on or is lifted from the instrument a switch is operatedcalled the hook-switch. The main function of this switch is to toggle betweentelephone-line and ringer, dialing & speech sections of the telephone. When thehandset is on the telephone then ringer section of the telephone is on while on liftingit ringer section is disconnected and dialing section is connected.

How the telephone call is made:

Telephone call is characterized into two sections:

1. Outgoing calls: Generally a voltage of 48V-60V DC always remains on thetelephone line but as the handset is picked-up the voltage limiter drops this voltageto 9-12V on hearing the dial tone it is confirmed that the apparatus is ready to workand after dialing the number a ringing pulse is send to the called party. When thecalling party picks-up the handset the billing meter of the exchange becomesactivated. There is a counter in the exchange, which counts the pulse and converts

them into calls.

2. Incoming calls: These are just opposite of outgoing calls. In the incoming callsthe telephone detects the ringing signal from the exchange and provides the ring. Atthe instance of ringing signal, there remains a voltage of 75-110V/20 Hz on thetelephone. A high voltage (AC) is sent from the ringer section of the exchange tostart the ringer circuit of the telephone. When the ringing signal is received it shouldbe properly isolated as it may give a shock. This ringing circuit is on until the handsetis not picked-up at the called party. The duration of this tone, if unattended, is 1minute after which an engage tone is heard. After lifting the handset a circuit is

established and a call is made.

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There are various powers providing circuits available in the exchange to run thecircuitry. These are broadly categorizedin two categories:

• Outside the exchange

• Inside the exchange

Outside the Exchange:

Since the voltage supplied in IndianSubcontinent is 220-volts/50 Hz AC butfor the normal working of the exchange48(46-53) volts of DC is required.

Hence a Rectifier circuit, backed withbattery array for power-failures, isused. This rectifier block not onlyrectifies the input supply but also worksas a battery charger. It is known asFloat rectifier cum charger.

Battery backup is utilized for smooth operation of the exchange during powerfailures. For battery back-up lead acid battery array is used in parallel to the supplyfrom the rectifier block, so that during power failures the exchange supplies are notterminated.

Inside the Exchange:

Inside the telephone exchange various types of power supplies are used for powering variousmodules (for example: - Line-cards, Ringer). Some of them are: -

-5 V 12 A +5 V 12 A

inside the exchange +12 V 6A.

From M.D.F. a number of cables, based upon therequirement of a place, are connected to cabinets. Onthe cabinets these cables are divided into cables of 20 pairs. Now every 20 pair cable goes to the distribution box (D.B.). At the D.B. this

20 pair cable is further divided into two parts of 10 pairs each. These pairs are thenconnected to the subscriber ports via jumpers. The line from these ports then goes tothe subscribers through single pair cables which are usually of P.V.C. type. Thesewires are connected to the instrument via Rosette-Box.

M.D.F

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This frame serves the following purposes: -

• It is place where both external and internal cables are terminated. The externalindividuals cable carry conductors from subscribers who are necessarily from thesame locality and as such their numbers cannot be in numerical order. On theother hand, the internal cable conductors come from apparatus side in numerical

order. This cross-section between the two cables is done on the M.D.F through jumper wires.

Old M.D.F

• It carries all the protectors used in the exchange. The different protectors that areused are (a) Fuses, (b) Heat coils, and (c) lightning protectors.

• This M.D.F is an ideal place for testing purpose. Both the internal and theexternal cables are available at this frame and, therefore, both external andinternal wiring and lines can be tested for this purpose.

New MDF in Exchange

I.D.F

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New MDF

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These frames like M.D.F. consists of a large number of verticals with horizontal cross-arms fitted with tag blocks at both the ends. The cable from M.D.F. is terminated onthe multiple sides from where connections are extended to metering and from theexchange side cables are run to the respected line-cards. The two tag blocks are joined by means of jumper wires as in the M.D.F., so that any subscriber can be givenconnection to any uniselector on the line-card. The subscriber and, therefore, their

uniselector are divided into different groups and it is necessary for these groups tooriginate more or less the same amount of traffic for smooth distribution amongdifferent trunks.

Various cards & card holder in EPBAX exchange

1.Analog extension card (Z-24) The alcatel z-24 extension card provide4400 omni connection and this card has 24 port. The cost of

this card is 952 $.

2.Digital extension card (UA-32)This card has 32 port

3. DIT Card used through proper line (ATR-2)These are direct inward dialing card.3*8 = 24 lines

4. Analog trunk card used as a junction to junction(NDDI)

The cost of this card is 852 $8*8 = 64 linesIf we dial a no. using this junction then

the actual no. is not shown at the user displayonly junction no. is shown

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5. CPU 3CPU is a central processing unit. These cards control

the over all functioning of the exchange cabinet.

6. INTOF

INTOF is a interface card. These card are used to interface all the cards with one another. 7. MMSFD

FLOPPY BOARD or FLOPPY DRIVE used by owner

8. SUVG

SUVG is a voice card. It gives the information if no. isbusy

9.IDTL8IDTL8 is a loop dialing card. It

dials a card repeatively untill the callis not transferred to the used.

10. PCM2PCM2 is a digital trunk

card used through OF (optical fiber)

11. GPA1 This card is used forconference call means this card willfunction when more then 1 user are

on call to a single person.

PRI CARDPRI Card is the standard four providing tele

communication services to the office. It is based on T1carrier.(T1) lines in the us. and the e carrier (E1) line inEurope. The T1 line consists of 24 channels. While E1 has 32.

Exchange cabinet

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Reck-1 Reck-0

Reck 0 - Bottem reckReck 1 - up reckReck 2 - down reck

Alcatel exchange

TELEPHONE LINES

In BHEL-Hardwar three types of telephone lines are used. They are: -

•MAX Lines

• EPABX Lines

• C-DOT Lines MAX Lines:

Before MAX Ex. Lines are used only Internal Exchange. But New (CORAL) MAX linesare used for both internal (Intercom) and external communication links BHEL.

EPABX Lines:

EPABX lines are used for both internal and external communication links in BHEL. If the user wants to dial outside the periphery of BHEL, he can use these lines. Thereare about 500 lines available here. These lines are distributed in 17 line-cards with 24line numbers in each. Its I.D.F. section has 40 tag blocks. 96 numbers available hereare connected via digital lines in which a host of facilities are provided that can beaccessed using code 69. C-DOT Lines:

These lines are the direct telephone lines from C-DOT The facility they provide iscalled DID (Direct Inward Dialing). It has 24 lines and any BHEL number starting withdigit 5 can be accessed using code 48.

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0-27 slots

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CONNECTION TYPES

Types of Connections:1. With wires i.e. Cables

Wireless Microwave Links through Satellite

Cables: Two types of Cables are used. They are:

1. Underground cables: These types of cables run under the earth and are basicallyused to connect the exchange to the subscriber's Distribution Box (D.B.). They arefurther of two types based upon their construction and the insulating materialused.

a. Paper core A.T.C. (Armored Tin Cable)b. Jelly filled A.T.C. (Armored Tin Cable)

2. Overhead cables: These types of cables are used to connect the equipmentsinside the exchange and to connect the peripheral devices to the subscriber'sDistribution Box

(DB) They are generally of P.V.C. type.

In an exchange, based upon the number of conductor pairs, following types of cablesare used:

• Single Pair cable

• 2 Pairs cable

• 5 Pairs cable

• 10 Pairs cable

• 20 Pairs cable

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• 50 Pairs cable100 Pairs cable

Color-coding:

TYPE COLOR OF WIRES

Single pair Blue-White

2 Pair cable Blue-White/Orange-White

5 Pair cable Blue-White/Orange-White/Green-White/Brown-White/Grey-White

10 Pair cable Blue-White/Orange-White/Green-White/Brown-White/Grey-White/Blue-Red/Orange-Red/Green-Red/Brown-Red/Grey-Red

20 Pair cable Blue-White/Orange-White/Green-White/Brown-White/Gray-White/Blue-White-blue/Orange-White-Blue/Green-White-Blue/Brown-White-Blue/Gray-White-Blue/Blue-White-Orange/Orange-White-Orange/Green-White-Orange/Brown-White-Orange/Gray-White-Orange/Blue-White-Green/Orange-White-Green/Green-White-Green/Brown-White-Green/Gray-White-Green.

For 100 pairs cable the color-coding is same as that of the above 20 pairs cableexcept that the mate color is changed after each bunch of 20 pairs.

PAIRMATE COLOR 1st 20 pairs White2nd 20 pairsYellow3rd 20 pairsBlack4th 20

pairsViolet5th 20 pairs Red

General faults occurring in an Exchange

There are mainly two types of faults that often occur in the Exchange. These arebasically

1. Faults that occur from Line2. Faults that occur due to Instrument

1.Faults that occur from Line

Due to line three types of faults may occur. They are categorized as under:

1. Break fault: They are also called as Disconnection faults. They can occur in theconnectors at home, in line or in exchange. In common they are broadly called as"Telephone is dead".

2. Loop fault: They are also called as Line-Shorting faults. In this fault connectorsare shorted prior the instrument forming a local loop. If unattended for a long timethey may cause severe damage to the Exchange.

3. Earth fault: This fault may occur due to:

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Fig.9 – Automatic Line Tester

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• wetting of connectors

• Water in Rosette-Box

• Weak insulation or

• Oxidation of copper wireConnectors can either touch from earth, with other connector or with any conductor(such as metallic table, frame etc.)

Problems that can occur due to line faults:1. Subscriber cannot dial a number.2. Ring Trip i.e. connection from the exchange breaks after one ring.3. False Ring4. Low speech5. One sided speech

Faults that occur due to instrument: These may be:

• The number is not being dialed• One way speech.

• Dial tone breaks after two or three rings. • From second subscriber bell is heard to be going but at first subscriber only dial

tone is heard.

• Instrument circuitry faulty.

• When loop or earth fault is received than exchange can be affected so it iswedged as soon as possible because if not wedge for longer it can damageline-card too.

To sense these faults first line-side is checked and then exchange side is checked atexchange. If however exchange side is correct then line faults after detection arehanded over to the concerned lineman for further checking.

Testing Procedure

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OPTICAL FIBER SYSTEM

Fiber optical transmission medium is fast emerging as an alternative and strongcompetitor to coaxial cables in telecommunication networks.

Long distance data transmission in electrical cables suffers from ground loopproblems. The merits of the optical fiber stem from the fact that the basic materialused in their construction is nonmetallic and electrically nonconductive.

In contrast, the nonmetallic and totally dielectric fiber optical cable are immune toradio frequency another electromagnetic interferences. Ground loop and commonmode voltage problem do not exist and data can be transmitted between points of vastly different potential. In optical cables the information is transmitted by packetsof photons which have no charge. There is no possibility of sparks or short circuitwhen a fiber is cut. The bandwidth high compared to that of the electrical cables. Thestandard RG-58 coaxial cable has bandwidth distance product of a typical opticalfiber is about 100 MHz-Km.

Fiber cables are about the thickness of a human hair any dirt obstructing the opticalport causes poor transmission. The thin dimension results in a low weight for givenlength when compared to electrical cables. However, being thin and somewhat brittlein nature, fiber tend to break easily if bent beyond a certain limit a direct viewing intothe optical point can be harmful to the eyes.

Broadband optical fiber system

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LIST OF SPECIAL USER FEATURES ON VARIOUSEXCHANGES

1. MAX (Coral India Pvt. LTD, NOIDA)

Manufacturer: Jeumont Schinedier, France

Capacity: 2700 lines

Call Pick Up: 89-xxxx to pick up a call ringing at another locationxxxx.

Call Transfer: 2 Parties conversing, any party can dial 3rd party, thenConversation among them Hang-up. The party on line nowtalks to 3rd party.

Party Conference: While speaking with a party:

(From Pulse Instrument: -- If CALLER requires dialing 3rdparty during conversation and maintaining talks, then dial 4.)(From Tone Instrument: -- If CALLER requires dialing 3rdparty during conversation and maintaining talks, then flash,and dial 4.)

Malicious Call Trace: Dial 29 during conversation, to trace a malicious call From aMAX Extension. Then enquire from 4999 or 4424.

Appointment Reminder: Dial 80-xx-yy {xx=hrs, yy=min}. To Cancel: Dial 27.

2. EPABX = ALCATEL 4400

Manufacturer: ALCATEL, FRANCE Capacity: 500 lines (96 DIGITAL, 404 ANALOG) Technology used: PCM - TDM

Tone Mode Dial: Dial # before no. {If instrument is not tone enabled)

Call Transfer: Hook FLASH: Do Hook Flash -On hearing prompt "Please dial." Dial the no., wait for partyto respond, and then disconnect.

Enquiry Call: FLASH (from Tone mode instrument.) or 2 (from Pulsemode)

During converse put the 1st party on HOLD. Then, dial a 3rd

party and speak.

Broker Call: (After ENQUIRY CALL): Dial 1 To go BACK & FORTH, between two parties (one party inconversation & other On HOLD)

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Conference-3 Party: While talking to 1st party, first make ENQUIRY CALL(Put on hold){FLASH from Tone; or 2 from Pulse}. Then - Dial 3rd party - Flash-- Dial 3.

Auto Callback: Dial 5 to book auto-callback when a busy PABX hangs up.(To cancel auto-callback request: Dial 67 or/and 848)

Password Modification: 847-0000-xxxx (0000=old password; xxxx = newPassword). This facility is available on STD enabledextensions only.

Last caller callback: 851 {to ring the last unattended PABX Caller}

Appointment Reminder: 852 then dial the time as {xx (hr) xx (min)} To cancel: 853

Last no. Redial: 854 User can use this if instrument doesn’t have a

Redial Button.

Call Pickup: 72 - XXXX to pick up a call ringing at another extension.

Call-Park / Retrieve: It is used during an incoming or outgoing call, to speakfrom a different set.

(To park from own (speaking) set: FLASH-855- dial ownextension number. Then “Hang-up". The call is now parked,and the other party is kept on hold.(To pick up from a different set: 855- dial own extension

number)(To pick up from own set (later, if not taken elsewhere) 855)

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MAINTENANCE

The subject of maintenance of Automatic Telephone Exchange can be broadlydivided under two categories: -

1. Prevention of Service Failures.2. Location of Faults and their removal.

Prevention of Service Failures can be done in following ways: -

1. Suitable design and adoption of suitable adjustment standards of theequipment parts of the exchange can minimize failures in service.

2. Some preventive measures may also reduce service failures viz. keeping therooms dust free, maintaining temperature and humidity under tolerable limitsusing air-conditioners.

3. Routine inspection, routine tests and routine adjustments also help inpreventing service failures. When faults occur in some parts of the exchange,they should be detected and removed as quickly as possible.

Various tools are also used to check the faults in the telephone lines and for checkingfault inside the exchange.

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