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INDEX

About BSNL 2

What is communication

Introduction: The Evolution of Mobile

Telephone Systems

3

4

GSM 7

GSM Network 12

GSM Network Areas 16

GSM Specification 18

Subscribers Identity Module 19

GSM Subscriber Services 21

Supplementary Services

Types of exchanges

EWSD

MDF

Air Conditioning

22

24

25

26

27

1



1. About BSNL

Bharat Sanchar Nigam Ltd. Formed in oct. 2000, is world’s 7th largest

telecommunications company providing comprehensive range of telecom

services in India: wire line, CDMA mobile, GSM mobile, internet,

broadband, carrier services. Within a span it has become the one of the

largest public sector unit in India.

BSNL is the only service provider, making focused efforts and planned

initiatives to bridge the rural –urban digital divide ICT sector. In fact there is

no telecom operator in the country to beat it reach with its wide network

giving services I every nook & corner of country and operates across India

except Delhi & Mumbai.

BSNL cellular service cellone, has more than 20.7 million cellular

customers, garnering 24 % of all mobile users as its subscribers. That means

that almost every fourth mobile user in the country has a BSNL connection.

In basic services, BSNL is miles ahead of its rivals, with 35.1 million Basic

Phone Subscribers i.e. 85 % share of the subscribers and 92 % share in

revenue terms.

BSNL has set up a world class multi-gigabit, multi-protocol convergent IPinfrastructure that provides convergent services like voice, data and video

through the same Backbone and broadband access network. At present there

are 0.6 million Data one broadband customers.

The turnover, nationwide coverage, reach, comprehensive range of the

telecom services and the desire to excel has made BSNL the no. 1 telecom

company of India.

2



What is Communication?

Communication can be defined as transfer of information from one

point to another as per the desire of the user under control of system.

The following elements are in communication network:

Switching,Transmission,

Signalling,

Network elements.

SWITCHING: It is basically establishing temporary path or connection b/w

two points. There are two modes of switching:-

CIRCUIT SWITCHING:- Is a telecommunications technology by which two

network nodes establish a dedicated communications channel (circuit)

connecting them for the duration of the communication session before the

nodes may communicate.

PACKET SWITCHING:- In which packets are transmitted over a shared

network which routes each packet independently from all others and

allocates transmission resources as needed.

3



2. Introduction: The Evolution of Mobile Telephone

Systems

Cellular is one of the fastest growing and most demanding

telecommunications applications. Today, it represents a continuously

increasing percentage of all new telephone subscriptions around the world.

Currently there are more than 45 million cellular subscribers worldwide, and

nearly 50 percent of those subscribers are located in the United States. It is

forecasted that cellular systems using a digital technology will become the

universal method of telecommunications. By the year 2005, forecasters

predict that there will be more than 100 million cellular subscribers

worldwide. It has even been estimated that some countries may have more

mobile phones than fixed phones by the year 2000.

Figure 1. Cellular Subscriber Growth Worldwide

The concept of cellular service is the use of low-power transmitters where

frequencies can be reused within a geographic area. The idea of cell-based

mobile radio service was formulated in the United States at Bell Labs in the

early 1970s. However, the Nordic countries were the first to introduce

cellular services for commercial use with the introduction of the NordicMobile Telephone (NMT) in 1981.

4



Cellular systems began in the United States with the release of the advanced

mobile phone service (AMPS) system in 1983. The AMPS standard was

adopted by Asia, Latin America, and Oceanic countries, creating the largest

potential market in the world for cellular.

In the early 1980s, most mobile telephone systems were analog rather than

digital, like today's newer systems. One challenge facing analog systems wasthe inability to handle the growing capacity needs in a cost-efficient manner.

As a result, digital technology was welcomed. The advantages of digital

systems over analog systems include ease of signaling, lower levels of

interference, integration of transmission and switching, and increased ability to

meet capacity demands. Table 1 charts the worldwide development of

mobile telephone systems.

Year Mobile System

1981 Nordic Mobile Telephone (NMT) 450

1983 American Mobile Phone System (AMPS)

1985 Total Access Communication System (TACS)

1986 Nordic Mobile Telephony (NMT) 900

1991 American Digital Cellular (ADC)

1991 Global System for Mobile Communication (GSM)

1992 Digital Cellular System (DCS) 1800

1994 Personal Digital Cellular (PDC)

1995 PCS 1900—Canada

1996 PCS—United States

Table 1. The Development of Mobile Telephone Systems

Throughout the evolution of cellular telecommunications, various systems

have been developed without the benefit of standardized specifications. This

presented many problems directly related to compatibility, especially with

5



the development of digital radio technology. The GSM standard is intended

to address these problems.

From 1982 to 1985 discussions were held to decide between building an

analog or digital system. After multiple field tests, a digital system was

adopted for GSM. The next task was to decide between a narrow or

broadband solution. In May 1987, the narrowband time division multipleaccess (TDMA) solution was chosen.

3. GSM

6



The growth of cellular telephone systems started in the early 1980s,

particularly in Europe. The lack of a technological standardization prompted

the European Conference of Postal and Telecommunications

Administrations (CEPT) to create the Group Special Mobile (GSM) in 1982

with the objective of developing a standard for a mobile telephone system

that could be used across Europe

In 1989, GSM responsibility was transferred to the European

Telecommunications Standards Institute (ETSI), and phase I of the GSM

specifications were published in 1990. The first GSM network was launched

in 1991 by Radiolinja in Finland. By the end of 1993, over a million

subscribers were using GSM phone networks being operated by 70 carriers

across 48 countries.[

The Global System for Mobile communications (GSM: originally from

Group Special Mobile) is the most popular standard for mobile phones in the

world. GSM service is used by over 2 billion people across more than 212

countries and territories. Its ubiquity makes international roaming very

common between mobile phone operators, enabling subscribers to use their

phones in many parts of the world. GSM differs significantly from its

predecessors in that both signaling and speech channels are digital call

quality, and so is considered a second generation (2G) mobile phone system.

This has also meant that data communication was built into the system from

the 3rd Generation Partnership Project (3GPP).

7

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The GSM logo is used to identify compatible handsets and equipment

The key advantage of GSM systems to consumers has been higher digital

voice quality and low cost alternatives to making calls, such as the Short

message service (SMS, also called "text messaging"). The advantage for

network operators has been the ease of deploying equipment from any

vendors that implements the standard. Like other cellular standards, GSM

allows network operators to offer roaming services so that subscribers can

use their phones on GSM networks all over the world.

Newer versions of the standard were backward-compatible with the original

GSM phones. For example, Release '97 of the standard added packet data

capabilities, by means of General Packet Radio Service (GPRS). Release '99

introduced higher speed data transmission using Enhanced Data Rates for

GSM Evolution About GSM

Radio interface

GSM is a cellular network, which means that mobile phones connect to it by

searching for cells in the immediate vicinity. GSM networks operate in four

different frequency ranges. Most GSM networks operate in the 900 MHz or

1800 MHz bands. Some countries in the Americas (including Canada andthe United States) use the 850 MHz and 1900 MHz bands because the 900

and 1800 MHz frequency bands were already allocated.

The rarer 400 and 450 MHz frequency bands are assigned in some countries,

notably Scandinavia, where these frequencies were previously used for first-

generation systems.

In the 900 MHz band the uplink frequency band is 890-915 MHz, and the

downlink frequency band is 935-960 MHz. This 25 MHz bandwidth is

subdivided into 124 carrier frequency channels, each spaced 200 kHz apart.

Time division multiplexing is used to allow eight full-rate or sixteen half-

rate speech channels per radio frequency channel. There are eight radio

timeslots (giving eight burst periods) grouped into what is called a TDMA

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frame. Half rate channels use alternate frames in the same timeslot. The

channel data rate is 270.833 kbit/s, and the frame duration is 4.615 ms.

The transmission power in the handset is limited to a maximum of 2 watts in

GSM850/900 and 1 watt in GSM1800/1900.

GSM has used a variety of voice codes to squeeze 3.1 kHz audio into between 6 and 13 kbit/s. Originally, two codecs, named after the types of

data channel they were allocated, were used, called "Full Rate" (13 kbit/s)

and "Half Rate" (6 kbit/s). These used a system based upon linear predictive

coding (LPC). In addition to being efficient with bit rates, these codecs also

made it easier to identify more important parts of the audio, allowing the air

interface layer to prioritize and better protect these parts of the signal.

GSM was further enhanced in 1997 with the GSM-EFR codec, a 12.2 kbit/s

codec that uses a full rate channel. Finally, with the development of UMTS,

EFR was refactored into a variable-rate codec called AMR-Narrowband,

which is high quality and robust against interference when used on full rate

channels, and less robust but still relatively high quality when used in good

radio conditions on half-rate channels.

There are four different cell sizes in a GSM network - macro, micro, Pico

and umbrella cells. The coverage area of each cell varies according to the

implementation environment. Macro cells can be regarded as cells where the base station antenna is installed on a mast or a building above average roof

top level. Micro cells are cells whose antenna height is under average roof

top level; they are typically used in urban areas. Pico cells are small cells

whose coverage diameter is a few dozen meters; they are mainly used

indoors. Umbrella cells are used to cover shadowed regions of smaller cells

and fill in gaps in coverage between those cells.

Cell horizontal radius varies depending on antenna height, antenna gain and

propagation conditions from a couple of hundred meters to several tens of

9



kilometers. The longest distance the GSM specification supports in practical

use is 35 km or 22 miles. There are also several implementations of the

concept of an extended cell, where the cell radius could be double or even

more, depending on the antenna system, the type of terrain and the timing

advance.

Indoor coverage is also supported by GSM and may be achieved by using anindoor picocell base station, or an indoor repeater with distributed indoor

antennas fed through power splitters, to deliver the radio signals from an

antenna outdoors to the separate indoor distributed antenna system. These

are typically deployed when a lot of call capacity is needed indoors, for

example in shopping centers or airports. However, this is not a prerequisite,

since indoor coverage is also provided by in-building penetration of the

radio signals from nearby cells.

The modulation used in GSM is Gaussian minimum-shift keying (GMSK), a

kind of continuous-phase frequency shift keying. In GMSK, the signal to be

modulated onto the carrier is first smoothed with a Gaussian low-pass filter

prior to being fed to a frequency modulator, which greatly reduces the

interference to neighboring channels (adjacent channel interference).

DETAILS:

A nearby GSM handset is usually the source of the "dit dit dit, dit dit dit, ditdit dit" signal that can be heard from time to time on home stereo systems,

televisions, computers, and personal music devices. When these audio

devices are in the near field of the GSM handset, the radio signal is strong

enough that the solid state amplifiers in the audio chain function as a

detector. The clicking noise itself represents the power bursts that carry the

TDMA signal. These signals have been known to interfere with other

electronic devices, such as car stereos and portable audio players. This is a

form of RFI, and could be mitigated or eliminated by use of additional

shielding and/or bypass capacitors in these audio devices. However, the

increased cost of doing so is difficult for a designer to justify..

10



4. The GSM Network

Multiple Access

TDMA/FDMA/FDA

Uplink frequency(mobile to base) 890-915 Mhz

Downlink frequency(base to mobile ) 935-960 Mhz

Channel Bandwidth 200 Khz

Number of channels 124

Channels/carrier 8(full rate),16(half rate)

Frame duration 4.6ms

Interleaving duration 40ms

Modulation GMSK

Speech coding method RPE-LTE convolution

Speech coder bit rate 13kb/s (full rate)

Associated control channel Extra frame

Handoff scheme Mobile assisted

Mobile station power levels 0.8, 2,58 w

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The Switching System

The switching system (SS) is responsible for performing call processing and

subscriber-related functions. The switching system includes the following

functional units.

•

Home location registers (HLR) —The HLR is a database used for storage and management of subscriptions. The HLR is considered the

most important database, as it stores permanent data about

subscribers, including a subscriber's service profile, location

information, and activity status. When an individual buys a

subscription from one of the PCS operators, he or she is registered in

the HLR of that operator.

• Mobile services switching center (MSC) —The MSC performs the

telephony switching functions of the system. It controls calls to andfrom other telephone and data systems. It also performs such

functions as toll ticketing, network interfacing, common channel

signaling, and others.

• Visitor location registers (VLR) —The VLR is a database that

contains temporary information about subscribers that is needed by

the MSC in order to service visiting subscribers. The VLR is always

integrated with the MSC. When a mobile station roams into a new

MSC area, the VLR connected to that MSC will request data about themobile station from the HLR. Later, if the mobile station makes a call,

the VLR will have the information needed for call setup without

having to interrogate the HLR each time.

• Authentication center (AUC) —A unit called the AUC provides

authentication and encryption parameters that verify the user's identity

and ensure the confidentiality of each call. The AUC protects network

operators from different types of fraud found in today's cellular world.

• equipment identity register (EIR) —The EIR is a database thatcontains information about the identity of mobile equipment that

prevents calls from stolen, unauthorized, or defective mobile stations.

The AUC and EIR are implemented as stand-alone nodes or as a

combined AUC/EIR node.

13



The Base Station System (BSS)

All radio-related functions are performed in the BSS, which consists of base

station controllers (BSCs) and the base transceiver stations (BTSs).

• BSC —The BSC provides all the control functions and physical links

between the MSC and BTS. It is a high-capacity switch that providesfunctions such as handover, cell configuration data, and control of

radio frequency (RF) power levels in base transceiver stations. A

number of BSCs are served by an MSC.

• BTS —The BTS handles the radio interface to the mobile station. The

BTS is the radio equipment (transceivers and antennas) needed to

service each cell in the network. A group of BTSs are controlled by a

BSC.

The Operation and Support System

The operations and maintenance center (OMC) is connected to all equipment

in the switching system and to the BSC. The implementation of OMC is

called the operation and support system (OSS). The OSS is the functional

entity from which the network operator monitors and controls the system.

The purpose of OSS is to offer the customer cost-effective support for

centralized, regional, and local operational and maintenance activities that

are required for a GSM network. An important function of OSS is to providea network overview and support the maintenance activities of different

operation and maintenance organizations.

14



Additional Functional Elements

Other functional elements shown in Figure 2 are as follows:

• Message center (MXE) —The MXE is a node that provides

integrated voice, fax, and data messaging. Specifically, the MXE

handles short message service, cell broadcast, voice mail, fax mail, e-mail, and notification.

• Mobile service node (MSN) —The MSN is the node that handles the

mobile intelligent network (IN) services.

• Gateway mobile services switching center (GMSC) —A gateway is

a node used to interconnect two networks. The gateway is often

implemented in an MSC. The MSC is then referred to as the GMSC.

• GSM interworking unit (GIWU) —The GIWU consists of both

hardware and software that provides an interface to various networks

for data communications. Through the GIWU, users can alternate

between speech and data during the same call. The GIWU hardware

equipment is physically located at the MSC/VLR.

15



5. GSM Network Areas

The GSM network is made up of geographic areas. As shown in Figure 3,

these areas include cells, location areas (LAs), MSC/VLR service areas, and public land mobile network (PLMN) areas.

Figure 3. Network Areas

The cell is the area given radio coverage by one base transceiver station. The

GSM network identifies each cell via the cell global identity (CGI) number

assigned to each cell. The location area is a group of cells. It is the area in

which the subscriber is paged. Each LA is served by one or more base

station controllers, yet only by a single MSC (see Figure 4). Each LA is

assigned a location area identity (LAI) number.

16



Figure 4. Location Areas

An MSC/VLR service area represents the part of the GSM network that is

covered by one MSC and which is reachable, as it is registered in the VLR

of the MSC (see Figure 5).

Figure 5. MSC/VLR Service Areas

The PLMN service area is an area served by one network operator (see

Figure 6 ).

6. GSM Specifications

17



Before looking at the GSM specifications, it is important to understand the

following basic terms:

• bandwidth —the range of a channel's limits; the broader the

bandwidth, the faster data can be sent

• bits per second (bps) —a single on-off pulse of data; eight bits are

equivalent to one byte

• frequency —the number of cycles per unit of time; frequency is

measured in hertz (Hz)

• kilo (k) —kilo is the designation for 1,000; the abbreviation kbps

represents 1,000 bits per second

• megahertz (MHz) —1,000,000 hertz (cycles per second)

• milliseconds (ms) —one-thousandth of a second

• watt (W) —a measure of power of a transmitter

Specifications for different personal communication services (PCS) systems

vary among the different PCS networks. Listed below is a description of the

specifications and characteristics for GSM.

• Frequency band —The frequency range specified for GSM is 1,850

to 1,990 MHz (mobile station to base station).

•

Duplex distance —The duplex distance is 80 MHz. Duplex distance isthe distance between the uplink and downlink frequencies. A channel

has two frequencies, 80 MHz apart.

• Channel separation —The separation between adjacent carrier

frequencies. In GSM, this is 200 kHz.

• Modulation— Modulation is the process of sending a signal by

changing the characteristics of a carrier frequency. This is done in

GSM via Gaussian minimum shift keying (GMSK).

• Transmission rate —GSM is a digital system with an over-the-air bit

rate of 270 kbps.

• Access method —GSM utilizes the time division multiple access

(TDMA) concept. TDMA is a technique in which several different

• calls may share the same carrier. Each call is assigned a particular

time slot.

18



• Speech coder —GSM uses linear predictive coding (LPC). The

purpose of LPC is to reduce the bit rate. The LPC provides parameters

for a filter that mimics the vocal tract. The signal passes through this

filter, leaving behind a residual signal. Speech is encoded at 13 kbps.

7. Subscriber identity module

A SIM for Bell Mobility (Canada)

One of the key features of GSM is the Subscriber Identity Module (SIM),

commonly known as a SIM card. The SIM is a detachable smart card

containing the user's subscription information and phonebook. This allows

the user to retain his or her information after switching handsets.

Alternatively, the user can also change operators while retaining the handset

simply by changing the SIM. Some operators will block this by allowing the

phone to use only a single SIM, or only a SIM issued by them; this practice

is known as SIM locking, and is illegal in some countries.

In Australia, Canada, Europe and the United States many operators lock the

mobiles they sell. This is done because the price of the mobile phone is

typically subsidized with revenue from subscriptions, and operators want to

try to avoid subsidizing competitor's mobiles. A subscriber can usuallycontact the provider to remove the lock for a fee, utilize private services to

remove the lock, or make use of ample software and websites available on

the Internet to unlock the handset themselves. While most web sites offer the

unlocking for a fee, some do it for free. The locking applies to the handset,

identified by its International Mobile Equipment Identity (IMEI) number,

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not to the account (which is identified by the SIM card). It is always possible

to switch to another (non-locked) handset if such a handset is available.

Some providers will unlock the phone for free if the customer has held an

account for a certain time period. Third party unlocking services exist thatare often quicker and lower cost than that of the operator. In most countries,

removing the lock is legal. Cingular and T-Mobile provide free unlocking

services to their customers after 3 months of subscription

In countries like Belgium, India, Indonesia and Pakistan, etc., all phones are

sold unlocked. However, in Belgium, it is unlawful for operators there to

offer any form of subsidy on the phone's price. This was also the case in

Finland until April 1, 2006, when selling subsidized combinations of

handsets and accounts became legal, though operators have to unlock phones

free of charge after a certain period (at most 24 months).

8. GSM Subscriber Services

There are two basic types of services offered through GSM: telephony (also

referred to as teleservices) and data (also referred to as bearer services).

Telephony services are mainly voice services that provide subscribers with

the complete capability (including necessary terminal equipment) to

communicate with other subscribers. Data services provide the capacity

20



necessary to transmit appropriate data signals between two access points

creating an interface to the network. In addition to normal telephony and

emergency calling, the following subscriber services are supported by GSM:

• Dual-tone multi frequency (DTMF) —DTMF is a tone signaling

scheme often used for various control purposes via the telephone

network, such as remote control of an answering machine. GSMsupports full-originating DTMF.

• Facsimile group III —GSM supports CCITT Group 3 facsimile. As

standard fax machines are designed to be connected to a telephone

using analog signals, a special fax converter connected to the

exchange is used in the GSM system. This enables a GSM–connected

fax to communicate with any analog fax in the network.

• Short message services —A convenient facility of the GSM network

is the short message service. A message consisting of a maximum of

160 alphanumeric characters can be sent to or from a mobile station.

This service can be viewed as an advanced form of alphanumeric

paging with a number of advantages. If the subscriber's mobile unit is

powered off or has left the coverage area, the message is stored and

offered back to the subscriber when the mobile is powered on or has

reentered the coverage area of the network. This function ensures that

the message will be received.

• Cell broadcast —A variation of the short message service is the cell

broadcast facility. A message of a maximum of 93 characters can be

broadcast to all mobile subscribers in a certain geographic area.

Typical applications include traffic congestion warnings and reports

on accidents.

• Voice mail —This service is actually an answering machine within the

network, which is controlled by the subscriber. Calls can be forwarded

to the subscriber's voice-mail box and the subscriber checks for

messages via a personal security code.

• Fax mail —With this service, the subscriber can receive fax messages

at any fax machine. The messages are stored in a service center from

which they can be retrieved by the subscriber via a personal security

code to the desired fax number.

21



9. Supplementary Services

GSM supports a comprehensive set of supplementary services that can

complement and support both telephony and data services. Supplementary

services are defined by GSM and are characterized as revenue-generatingfeatures. A partial listing of supplementary services follows.

• Call forwarding — This service gives the subscriber the ability to

forward incoming calls to another number if the called mobile unit is

not reachable, if it is busy, if there is no reply, or if call forwarding is

allowed unconditionally.

• Barring of outgoing calls —This service makes it possible for a

mobile subscriber to prevent all outgoing calls.• Barring of incoming calls —This function allows the subscriber to

prevent incoming calls. The following two conditions for incoming

call barring exist: baring of all incoming calls and barring of incoming

calls when roaming outside the home PLMN.

• Advice of charge (AoC) —The AoC service provides the mobile

subscriber with an estimate of the call charges. There are two types of

AoC information: one that provides the subscriber with an estimate of

the bill and one that can be used for immediate charging purposes.AoC for data calls is provided on the basis of time measurements.

• Call hold —This service enables the subscriber to interrupt an

ongoing call and then subsequently reestablish the call. The call hold

service is only applicable to normal telephony.

• Call waiting —This service enables the mobile subscriber to be

notified of an incoming call during a conversation. The subscriber can

answer, reject, or ignore the incoming call. Call waiting is applicable

to all GSM telecommunications services using a circuit-switched

connection.

• Multiparty service —The multiparty service enables a mobile

subscriber to establish a multiparty conversation—that is, a

simultaneous conversation between three and six subscribers. This

service is only applicable to normal telephony.

22



• Calling line identification presentation/restriction —These services

supply the called party with the integrated services digital network

(ISDN) number of the calling party. The restriction service enables

the calling party to restrict the presentation. The restriction overrides

the presentation.

• Closed user groups (CUGs) —CUGs are generally comparable to a

PBX. They are a group of subscribers who are capable of only calling

themselves and certain numbers.

Types of Exchanges

OLDEN DAYS EXCHANGES:-

Magneto

CB (central battery)

23



Strauzer

Cross bar

NEW EXCHANGES:-

E10B

OCB-283EWSD

5ESS

AXE10

FETEX

C-DOT 256

C-DOT SBM

C-DOT MBMLC-DOT MBMXL

EWSD (Electronic Wheeler Systematic Digital)

SYSTEM FEATURES:-

EWSD is manufactured by M/s SIEMENS, Germany. The name is

abbreviated form of German equivalent of electronic switching

system digital. EWSD switch can support maximum 2,50,000

subscriber or 60,000 incoming or outgoing or both way trunks,

24



when working as a pure tandem exchange. It can carry 25,200

Erlang traffic and can withstand 1.4 million BHCA.

In India it was first setup in Calcutta.

H/w of EWSD:-

DLU: Digital Line Unit: Traffic capacity:100 erlang

Subscriber capacity: 944 half capacity:432

It is also called functional unit.

Subscriber line is terminated here.

LTG: Line and Trunks Groups:Digital trunks and DLU are connected here.

SN: Switching Network:

All the LTG are connected, interconnected subscriber line

and trunk to exchange.

CP: Coordination Processor:

It can provide call route and make all units work properly andfreely.

Each subscriber unit in EWSD carry out practically all the

task arising in there area independently.

CCNC: Common Channelling Network Control:

It transfers the message.

Main Distribution Frame (MDF)

At BSNL two types of networks are used:-

Indoor network

25



Outdoor network

Both the networks are connected on MDF. MDF is the main point

of exchange by which we can locate the total number of

connections and the density of the local area network. It is the

mirror of the telephone exchange by which we can see the working

culture of the employees.

Types of MDF:-

VERTICAL TYPE:- For small exchanges wall type MDF are

used. Capacity of this MDF is 2000 numbers. It is mounted

on the wall with the help of brackets and the underground

cables are terminated at upper side of the box.

VERTICAL TYPE:- It is used for a huge n/w like that more

than 2000 numbers. It is a long steel rack accessible from

both sides.

Safety point:-

Use of GD tube (gas discharge tube) on vertical of each

subscriber.

Every pillar or cabinet is properly earthed.

Each vertical connected with earthed wire of main Earthing.

AIR CONDITIONING

Air conditioning is an essential requirement for telecom

installation as electronic equipment. It can work satisfactorily in

26



controlled environment condition. This air conditioning system

performs following functions:-

Maintaining air at desired temperature.

Control moisture content of air.

Circulate air properly.

Air conditioning system has refrigeration system which allowstransfer of heat from cooling space to a location where heat can be

easily discarded. The transfer of heat is facilitated by the change of

state as refrigerant needs latent heat to change the state from liquid

to gas at its boiling point. The refrigerant has a much lower BP and

changing pressure varies the boiling point.

The refrigerants used are ammonia, feron-12, feron-22.

Properties of refrigerant:-

LATENT HEAT OF VAPOURIZATION:- It should be high as it

will result in smaller amount of refrigerant for given capacity of air

condition.

CONDENSING PRESSURE:- It should be low otherwise there

will be large expenditure on heavy construction of condenser and

piping.

FREEZING TEPERATURE:- It should be below the evaporating

temperature otherwise there will be ice formation in the air

conditioner.

TOXCITY:- It should be non-toxic, non inflammable and non-

corrosive further the detection of leaks should be easy and should

have very less environment impact.

Components of AC system:-

27



COMPRESSOR:- Compresses and discharge the refrigerant in gas

form to condenser at high pressure because of rapid compression

refrigerant becomes hot.

CONDENSER:- It is intended to cooling the gases and liquefying

under pressure and allow it in the evaporator under low pressure.

EXPANSION VALVE:- Function is to control a regular rate flowof liquid from under pressure and allow it in the evaporator under

low pressure.

EVAPORATOR:- Constitutes cooling unit in which liquid from

under low pressure evaporates.

Types of AC Systems:-

WINDOW TYPE AC:- They are completely self contained unit

with compressor, condenser, evaporator, refrigerating piping all

assembled in compact single unit.

SPLIT TYPE AC:- In this the condenser and compressor unit

(outdoor unit) and cooling coil (indoor unit) are housed in two

separates enclosures and both the indoor and outdoor unit are

connected to refrigerant pipeline and it should not be more than

30ft.

PACKAGE TYPE AC:- These are also very similar the window

model but are very much bigger in size and therefore installed on

the floors. It can be installed in AC space with or without duct

system. The control panel is conveniently located on unit itself.

CENTRAL AC Plant:- It becomes a necessity when the air of a

conditioning is large. The system is highly flexible and better

controls are possible.

Factors affecting AC load:-

28



Orientation and location of the building.

Building material used.

Number and types of windows used.

Utility of space.

Physical dimensions of space.

Lighting

Occupancy.

Appliance and equipment.

Ventilation

29



PREFACE

Industrial training is must for every student pursuing professional

degree because the ultimate goal of every student is to get the

information the industrial training helps us to get an idea of things.We should known in order to get a good job i.e. have a

good professional carrier. Industrial training teaches us a lot of

things. It helps us to know the kind of environment we would be

getting in an industry and help us to get with the kind of

environment. Industrial training helps us to know what kind of

grade an engineer of specific branch plays in an industry. It help us

to get used to working in groups of known people in it teach usteam work because my work in industrial is accomplished by a

group and not an individual.

In totality the industrial teaches us industrial ethics. Some

advance technical knowledge how and help us to acquired with

industrial working style.

30



Acknowledgement

First of all, let us thank the Almighty God who is the most

graceful and merciful for His blessing that Contributed to the

successful completion of our project.

I would like to pay my sincere gratitude to Mr. A. K. Sharma

(D/E, I/D) boundary road, who gave me this opportunity to

undergo my summer training at BSNL, Meerut. I would also like

to thanks Mr. Vinod Kumar Yadav, who gave me his time to help

me in Switching, Power Plant, Engine Alternator, Transmission,

Indoor n/w, Outdoor n/w, different type of exchanges.

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