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1. COMPANY PROFILE

Every day we make phone calls from our telephone sets quite easily but are unaware

of the technology used behind it. The technologies used in telecommunication is a bit

complicated but at the same time interesting too.

Here it has been tried to give an idea of the different technologies used for

telecommunication by one of the biggest service provides to India, i.e., BHARAT

SANCHAR NIGAM LTD.

The service provided by BSNL to its customers is:-

-Basic local telephony

-National and International call service

-Mobile Communication

-Internet Service

The basic telephony i.e., the local call facility provided to the consumers by BSNL

comprises of the following:-

-Exchange

-Main Distribution Frame

-Line Connection

-Power Plant

The exchange is the basic part of telecommunication system. It is through this exchange that

a subscriber gets connected to different parts of the world by means of a telephone. There

are different types of exchanges depending upon the technology used.

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2. INTRODUCTION

All industries operate in a specific environment which keeps changing and the firms

in the business need to understand it to dynamically adjust their actions for best results. Like

minded firms get together to form associations in order to protect their common interests.

Other stake holders also develop a system to take care of their issues. Governments also

need to intervene for ensuring fair competition and the best value for money for its citizens.

This handout gives exposure on the Telecom Environment in India and also dwells on the

role of international bodies in standardizing and promoting Telecom Growth in the world.

The Indian postal and telecom sectors saw a slow and uneasy start. In 1850, the first

experimental electric telegraph line was started between and . In 1851, it was opened for

the use of. The Posts and Telegraphs department occupied a small corner of the Public

Works Department, at that time.

Subsequently, the construction of 4,000 miles (6,400 km) of telegraph lines

connecting Kolkata (then Calcutta) and Peshawar in the north along with Agra, (then

Bombay) through Sindwa Ghats, and well as and was started in November 1853. , who

pioneered the and in India, belonged to the Public Works Department, and worked towards

the development of telecom throughout this period. A separate department was opened in

1854 when telegraph facilities were opened to the public.

In 1880, two namely The Ltd. and The Anglo-Indian Telephone Company Ltd.

approached to establish the permission was refused on the grounds that the establishment of

telephones was a Government monopoly and that the Government itself would undertake

the work. In 1881, the Government later reversed its earlier decision and a licence was

granted to the Limited of for opening telephone exchanges at ,and and the first formal

telephone service was established in the country. On the 28th January 1882, Major E.

Baring, Member of the 's Council declared open the Telephone Exchanges in Calcutta,

Bombay and Madras. The exchange in Calcutta named the "Central Exchange", was opened

at third floor of the building at 7, Council House Street, with a total of 93 subscribers. Later

that year, Bombay also witnessed the opening of a telephone exchange.

2.1 Further milestones and developments

1907 - First Central Battery of telephones introduced in 1913-1914 - First Automatic

Exchange installed in kanpur.

1927 - Radio-telegraph system between the and India, with beam stations at khadki and

dhundh..

1933 - system inaugurated between the UK and India.

1953 - 12 channel carrier systemoduced.

1960 - First route commissioned between delhi and Kanpur

1975 - First system commissioned between Mumbai city and andheri telephone

exchanges.

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1979 - First optical fibre system for local junction commissioned at pune

1980 - First satellite earth station for domestic communications established

at scikandarabad.

1983 - First analog signal Stored Program Control exchange for trunk line

commissioned at Mumbai.

1984 – c-dot exchange established for indigenous development and production

of digital exchanges.

1995 - First mobile telephone service started on non-commercial basis on 15 August

1995 in delhi

1995 - Internet Introduced in India starting with Delhi, Bombay, Calcutta, Chennai and

Pune on 15 August 1995

2.2 Modern policies

All villages shall receive telecom facilities by the end of 2002.

A Communication Convergence Bill introduced in the Parliament on August 31, 2001

is presently before the Standing Committee of Parliament on Telecom and IT.

National Long Distance Service (NLD) is opened for unrestricted entry.

The International Long Distance Services (ILDS) have been opened to competition.

The basic services are open to competition.

In addition to the existing three, a fourth cellular operator, one each in four metros and

thirteen circles, has been permitted. Cellular operators have been permitted to provide

all types of mobile services including

voice and non-voice messages, data services and public call office utilizing any type of

network equipment, including circuit and/or package switches that meet certain required

standards

Policies allowing private participation have been announced as per the New Telecom

Policy (NTP), 1999 in several new services, which include Global Mobile Personal

Communication by Satellite (GMPCS) Service, digital Public Mobile Radio Trunked

Service (PMRTS) and Voice Mail/ Audiotex/ Unified Messaging Services.

Wireless Local Loop has been introduced to provide telephone connections in urban,

semi-urban and rural areas promptly.

Two telecom PSUs, VSNL and HTL have been disinvested.

Steps are being taken to fulfill Universal Service Obligation (USO), funding, and

administration.

A decision to permit Community Phone Service has been announced.

Multiple Fixed Service Providers (FSPs) licensing guidelines were announced.

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Internet Service Providers (ISPs) have been allowed to set up International Internet

Gateways, both Satellite and Landing stations for submarine optical fiber cables.

Two categories of infrastructure providers have been allowed to provide end-to-end

bandwidth and dark fiber, right of way, towers, duct space etc.

Guidelines have been issued by the Government to open up Internet telephony (IP).

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3. ABOUT THE EXCHANGE

In the field of a telephone exchange or telephone switch is a system of electronic

components that connects telephone calls. A central office is the physical building used to

house equipment including telephone switches, which make "work" in the sense of making

connections and relaying the speech information.

3.1 TYPES OF EXCHANGE

3.1.1 Manual exchange

3.1.2 Strowger exchange

3.1.3 Cross bar exchange

3.1.4 Electronics exchange (analog and digital exchange)

3.1.1 MANUAL EXCAHNGE

With manual service, the customer lifts the receiver off-hook and asks the operator to

connect the call to a requested number. Provided that the number is in the same central

office, the operator connects the call by plugging into the jack on

the switchboard corresponding to the called customer's line. If the call is to another central

office, the operator plugs into the trunk for the other office and asks the operator answering

(known as the "inward" operator) to connect the call.

3.1.2 STROWGER EXCHANGE

Strowger developed a system of automatic switching using an electromechanical switch

based around electromagnets and pawls. With the help of his nephew (Walter S. Strowger)

he produced a working model in 1888 .selector starts in the 'home' position and with each

'impulse' the wiper contacts would progress round the output bank to the next position. Each

output would be connected to a different subscriber, thus the caller could connect to any

other subscriber who was connected to that bank, without any manual assistance from an

operator.

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Figure 3.1 Diagram of a simple Selector

In Figure 1.1 (above), the selector has 10 outputs, so a caller can choose to connect to any

of 10 different subscribers by dialing any digit from 1 to 0 (0=10). This sort of automatic

selector is known as a Uni-selector, as it moves in just one plane (rotary).

By mounting several arcs of outlets on top of each other, the number of outlets can be

increased significantly but the wipers are then required to move both horizontally to select

a bank and then vertically to move around that bank to the required outlet. Such a selector

is known as a Two-Motion Selector. Two-motion selectors typically have 10 rows of 10

outlets, thus 100 possible outlets altogether. A two-motion selector can therefore accept two

dialed digits from a subscriber and route the call to any of 100 numbers. The selector 'wipers'

always start in their resting 'home' position. The first digit moves the selector vertically up

to the corresponding level and then the second digit moves the wipers around the contacts

of that level. This is shown in figure 1.2, below.

Figure 3.2 A Two-Motion "Final" Selector

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The type of selector shown above is known as a Final Selector as it takes the final two

digits of the number dialed. Most numbers dialed are several digits longer, and therefore

pass through a chain of selectors. Selectors previous to the Final Selectors are different; they

are called Group Selectors. Group selectors take only ONE digit from the caller, and step

up the number of levels according to the digit dialed. The rotary movement is then

automatic; the wipers search around that level to find a free outlet - i.e. the next free selector

in the chain. This is covered in more depth later.

3.1.3.CROSS BAR EXCHANGE

In , a crossbar switch (also known as cross-point switch, crosspoint switch, or matrix switch)

is a connecting multiple inputs to multiple outputs in a matrix manner. Originally the term

was used literally, for a matrix switch controlled by a grid of crossing . A crossbar switch is

an assembly of individual switches between multiple inputs and multiple outputs.

The switches are arranged in a matrix. If the crossbar switch has M inputs and N outputs,

then a crossbar has a matrix with M x N cross-points or places where the "bars" cross. At

each crosspoint is a switch; when closed, it connects one of M inputs to one of N outputs.

A given crossbar is a single layer, non-blocking switch. Collections of crossbars can be used

to implement multiple layer and/or blocking switches. A crossbar switching system is also

called a co-ordinate switching system.

3.1.4 ELECTRONICS EXCHANGE

It is based on the automatic control by stored programmed in computer linked to it. It cover

all the main drawbacks of above mentioned exchange. It may be digital or analog but mostly

digital electronics exchanges are now common. It base on the principal time division

switching or space division switching. Space division switching is used for analog

electronics exchange and time division switching is used for digital exchange.

Figure-3.3 Space Division switching System

In a space Division Switching system, a continuous physical path is set up between input

and output terminations. This path is separate for each connection and is held for the entire

duration of the call. Path for different connections is independent of each other. Once a

continuous path has been established., Signals are interchanged between the two

terminations. Such a switching network can employ either metallic or electronic cross

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points. Previously, usage of metallic cross-points using reed relays and all were favored.

They have the advantage of compatibility with the existing line and trunk signaling

conditions in the network.

3.1.4.1. Time Division Switching System

In Time Division Switching, a number of calls share the same path on time division sharing

basis. The path is not separate for each connection, rather, is shared sequentially for a

fraction of a time by different calls. This process is repeated periodically at a suitable high

The repetition rate is 8 KHz, i.e. once every 125 microseconds for transmitting speech on

telephone network, without any appreciable distortion. These samples are time multiplexed

with staggered samples of other speech channels, to enable sharing of one path by many

calls. The Time Division Switching was initially accomplished by Pulse Amplitude.

3.2 DIGITAL CARD

It is programmed data card which is used for automatic control of call set up and call

termination as well as providing various services to the customer. There are three types of

digital card which are as follow

3.2.1 TERMINATION CARD

3.2.2 SERVICE CARD

3.2.3 CONTROL CARD

3.2.1 Termination card: its main aim to connect the customer on trunk line .other features

of terminating card is battery feed, over voltage protection,check weather call is STD or

LOCAL or ISD

3.2.2 Service card: the service like dial tone ,call waiting ,call confrencing etc is given by

this card.

3.2.3Control card: it is there to see whether the call has been established or not. If

established then requisite unit has been established or not.

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4.Local and Trunk Network

4.1 Trunk Lines

The term Trunk Line in telecommunications refers to the high-speed connection

between telephone central offices in the. Trunk lines are always digital. The wiring between

central offices was originally just pairs of twisted copper wire (the twists in the wiring

prevented things known as crosstalk and noise). Because it is expensive to string up (or lay

trenches for buried cables), the phone company researched ways in which to carry more data

over the existing copper lines. This was achieved by using. Later, when fiber-optic

technology became available, phone companies upgraded their trunk lines to fiber optics

and used statistical time-division multiplexing, , coarse or dense wave division multiplexing

and optical switching to further improve transmission speeds.

The signaling information exchanged between different exchanges via inter

exchange trunks for the routing of calls is termed as Inter exchange Signaling. Earlier in

band /out of band frequencies were used for transmitting signaling information. Later on,

with the emergence of PCM systems, it was possible to segregate the signaling from the

speech channel. A trunk line is a connecting (or other switching equipment), as

distinguished from local loop circuit which extends from telephone exchange switching

equipment to individual or information origination/termination equipment. When dealing

with a private branch exchange (PBX), trunk lines are the phone lines coming into the PBX

from the telephone provider. This differentiates these incoming lines from extension

telephone lines that connect the PBX to (usually) individual phone sets. Trunking saves cost,

because there are usually fewer trunk lines than extension lines, since it is unusual in most

offices to have all extension lines in use for external calls at once. Trunk lines transmit voice

and data in formats such as analog, digital signal 1, ISDN or primary rate interface. The dial

tone lines for outgoing calls are called DDCO (Direct Dial Central Office) trunks.

A travelling over a trunk line is not actually flowing any faster. The electrical signal

on a voice line takes the same amount of time to traverse the wire as a similar length trunk

line. What makes trunk lines faster is that the has been altered to carry more data in less

time using more advanced multiplexing and techniques. If you compared a voice line and

a trunk line and put them side by side and observed them, the first pieces of information

arrive simultaneously on both the voice and trunk line. However, the last piece of

information would arrive sooner on the trunk line. No matter what, you can't break the laws

of physics. Electricity over copper or laser light over fiber optics, you cannot break the speed

though that has rarely stopped uneducated IT or IS managers from demanding that cabling

perform faster instead of upgrading equipment.

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Trunk lines can contain thousands of simultaneous calls that have been combined using.

These thousands of calls are carried from one central office to another where they can be

connected to a de-multiplexing device and switched through digital access cross connecting

switches to reach the proper exchange and local phone number.

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5. PCM

A long distance or local telephone conversation between two persons could

be provided by using a pair of open wire lines or underground cable as early as

mid of 19th century. However, due to fast industrial development and an increased

telephone awareness, demand for trunk and local traffic went on increasing at a rapid

rate. To cater to the increased demand of traffic between two stations or between

two subscribers at the same station we resorted to the use of an increased number

of pairs on either the open wire alignment, or in underground cable. This could

solve the problem for some time only as there is a limit to the number of open

wire pairs that can be installed on one alignment due to headway consideration and

maintenance problems. Similarly increasing the number of open wire pairs that can

be installed on one alignment due to headway consideration and maintenance problems.

Similarly increasing the number of pairs to the underground cable is uneconomical

and leads to maintenance problems. It, therefore became imperative to think of new

technical innovations which could exploit the available bandwidth of transmission media

such as open wire lines or underground cables to provide more number of circuits on one

pair. The technique used to provide a number of circuits using a single transmission link is

called Multiplexing.

5.1Basic Requirements for PCM System:

To develop a PCM signal from several analogue signals, the following processing steps are

required:

-Filtering

-Sampling

-Quantising

-Encoding

5.2 Duplexing Methodology:

Duplexing is the technique by which the send and receive paths are separated over the

medium, since transmission entities (modulator, amplifiers, demodulators) are involved.

There are two types of Duplexing:

5.2.1 Frequency Division Duplexin

5.2.2 Time Division Duplexing (TDD)

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5.2.1 Frequency Division Duplexing (FDD): Different frequencies are used for send and

receive paths and hence there will be a forward band and reverse band. Duplexer is needed

if simultaneous transmission (send) and reception (receive) methodology is adopted.

Frequency separation between forward band and reverse band is constant.

5.2.2 Time Division Duplexing (TDD): TDD uses different time slots for transmission and

reception paths. Single radio frequency can be used in both the directions instead of two as

in FDD. No duplexer is required. Only a fast switching synthesizer, RF filter path and fast

antenna switch are needed. It increases the battery life of mobile pho

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6. FIBER-OPTICS COMMUNICATION

6.1 FIBER OPTICS:

The use and demand for optical fiber has grown tremendously and optical-fiber

applications are numerous. Telecommunication applications are widespread, ranging from

global networks to desktop computers. These involve the transmission of voice, data, or

video over distances of less than a meter to hundreds of kilometers, using one of a few

standard fiber designs in one of several cable designs.

Carriers use optical fiber to carry plain old telephone service (POTS) across their

nationwide networks. Local exchange carriers (LECs) use fiber to carry this same service

between central office switches at local levels, and sometimes as far as the neighborhood or

individual home (fiber to the home [FTTH]).

Optical fiber is also used extensively for transmission of data. Multinational firms

need secure, reliable systems to transfer data and financial information between buildings

to the desktop terminals or computers and to transfer data around the world. Cable television

companies also use fiber for delivery of digital video and data services. The high bandwidth

provided by fiber makes it the perfect choice for transmitting broadband signals, such as

high-definition television (HDTV) telecasts. Intelligent transportation systems, such as

smart highways with intelligent traffic lights, automated tollbooths, and changeable

message signs, also use fiber-optic-based telemetry systems.

Another important application for optical fiber is the biomedical industry. Fiber-

optic systems are used in most modern telemedicine devices for transmission of digital

diagnostic images. Other applications for optical fiber include space, military, automotive,

and the industrial sector.

6.2 ADVANTAGES OF FIBRE OPTICS :

Fiber Optics has the following advantages :

• SPEED: Fiber optic networks operate at high speeds - up into the gigabits

•BANDWIDTH:large carrying capacity

• DISTANCE: Signals can be transmitted further without needing to be "refreshed" or

strengthened.

RESISTANCE: Greater resistance to electromagnetic noise such as radios, motors or

other nearby cables.

• MAINTENANCE: Fiber optic cables costs much less to maintain.

6.3 Fiber Optic System :

Optical Fibre is new medium, in which information (voice, Data or Video) is transmitted

through a glass or plastic fibre, in the form of light, following the transmission sequence

give below :

6.3.1 Information is Encoded into Electrical Signals.

6.3.2 Electrical Signals are Coverted into light Signals.

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6.3.3 Light Travels Down the Fiber.

6.3.4 A Detector Changes the Light Signals into Electrical Signals.

6.3.5 Electrical Signals are Decoded into Information.

Inexpensive light sources available. Repeater spacing increases along with operating speeds

because low loss fibres are used at high data rates.

Figure-6.1 Principle of Operation

6.4 Total Internal Reflection

The Reflection that Occurs when a Ligh Ray Travelling in One Material Hits a Different

Figure-6.2- total internal reflection

Material and Reflects Back into the Original Material without any loss of light.

6.5 PROPAGATION OF LIGHT THROUGH FIBER

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The optical fiber has two concentric layers called the core and the cladding. The

inner core is the light carrying part. The surrounding cladding provides the difference

refractive index that allows total internal reflection of light through the core. The index of

the cladding is less than 1%, lower than that of the core. Typical values for example are a

core refractive index of 1.47 and a cladding index of 1.46. Fiber manufacturers control this

difference to obtain desired optical fiber characteristics. Most fibers have an additional

coating around the cladding. This buffer coating is a shock absorber and has no optical

properties affecting the propagation of light within the fiber. Figure shows the idea of light

travelling through a fiber. Light injected into the fiber and striking core to cladding interface

at greater than the critical angle, reflects back into core, since the angle of incidence and

reflection are equal, the reflected light will again be reflected. The light will continue

zigzagging down the length of the fiber. Light striking the interface at less than the critical

angle passes into the cladding, where it is lost over distance. The cladding is usually

inefficient as a light carrier, and light in the cladding becomes attenuated fairly. Propagation

of light through fiber is governed by the indices of the core and cladding by Snell's law.

Such total internal reflection forms the basis of light propagation through a optical fiber.

This analysis consider only meridional rays- those that pass through the fiber axis each time,

they are reflected. Other rays called Skew rays travel down the fiber without passing through

the axis. The path of a skew ray is typically helical wrapping around and around the central

axis. Fortunately skew rays are ignored in most fiber optics analysis.

The specific characteristics of light propagation through a fiber depends on many

factors, including

- The size of the fiber.

- The composition of the fiber.

- The light injected into the fiber.

Figure-6.3- core and cladding.

50m and a cladding diameter of 125m.

Jacket

Cladding

Core

Cladding

Angle of

reflection

Angle of

incidence

Light at less than

critical angle is

absorbed in jacket

Jacket

Light is propagated by

total internal reflection

Jacket

Cladding

Core

(n2)

(n2)

Fig. Total Internal Reflection in an optical Fibre

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6.6 FIBER TYPES

The refractive Index profile describes the relation between the indices of the core and

cladding. Two main relationship exists :

(I) Step Index

(II) Graded Index

The step index fiber has a core with uniform index throughout. The profile shows a sharp

step at the junction of the core and cladding. In contrast, the graded index has a non-uniform

core. The Index is highest at the center and gradually decreases until it matches with that of

the cladding. There is no sharp break in indices between the core and the cladding.

By this classification there are three types of fibers :

(I) Multimode Step Index fiber (Step Index fiber)

(II) Multimode graded Index fiber (Graded Index fiber)

(III) Single- Mode Step Index fiber (Single Mode Fiber)

6.6.1 STEP-INDEX MULTIMODE FIBER- has a large core, up to 100 microns in

diameter. As a result, some of the light rays that make up the digital pulse may travel a direct

route, whereas others zigzag as they bounce off the cladding. These alternative pathways

cause the different groupings of light rays, referred to as modes, to arrive separately at a

receiving point. The pulse, an aggregate of different modes, begins to spread out, losing its

well-defined shape. The need to leave spacing between pulses to prevent overlapping limits

bandwidth that is, the amount of information that can be sent. Consequently, this type of

fiber is best suited for transmission over short distances, in an endoscope, for instance.

Figure-6.4 STEP-INDEX MULTIMODE FIBER

6.6.2 GRADED-INDEX MULTIMODE FIBER- contains a core in which the refractive

index diminishes gradually from the center axis out toward the cladding. The higher

refractive index at the center makes the light rays moving down the axis advance more

slowly than those near the cladding.

Figure-6.5 GRADED-INDEX MULTIMODE FIBER

Also, rather than zigzagging off the cladding, light in the core curves helically

because of the graded index, reducing its travel distance. The shortened path and the higher

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speed allow light at the periphery to arrive at a receiver at about the same time as the slow

but straight rays in the core axis. The result: a digital pulse suffers less dispersion.

6.6.3 SINGLE-MODE FIBER- has a narrow core (eight microns or less), and the index of

refraction between the core and the cladding changes less than it does for multimode fibers.

Light thus travels parallel to the axis, creating little pulse dispersion. Telephone and cable

television networks install millions of kilometers of this fiber every year.

Figure-6.6 SINGLE-MODE FIBER

6.7 OPTICAL FIBRE PARAMETERS

Optical fiber systems have the following parameters.

(I) Wavelength.

(II) Frequency.

(III) Window.

(IV) Attenuation.

(V) Dispersion.

(VI) Bandwidth.

6.7.1 WAVELENGTH

It is a characteristic of light that is emitted from the light source and is measures in

nanometers (nm). In the visible spectrum, wavelength can be described as the colour of the

light.

For example, Red Light has longer wavelength than Blue Light, Typical wavelength for

fibre use are 850nm, 1300nm and 1550nm all of which are invisible.

6.7.2 FREQUENCY

It is number of pulse per second emitted from a light source. Frequency is measured in units

of hertz (Hz). In terms of optical pulse 1Hz = 1 pulse/ sec.

6.7.3 WINDOW

A narrow window is defined as the range of wavelengths at which a fibre best operates.

6.7.4 ATTENUATION

Attenuation is defined as the loss of optical power over a set distance, a fibre with lower

attenuation will allow more power to reach a receiver than fibre with higher attenuation.

Attenuation may be categorized as intrinsic or extrinsic.

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6.7.4.1 INTRINSIC ATTENUATION

It is loss due to inherent or within the fibre. Intrinsic attenuation may occur as

i)-Absorption - Natural Impurities in the glass absorb light energy.

Scattering - Light Rays Travelling in the Core Reflect from small Imperfections into

a New Pathway that may be Lost through the cladding.

Figure-6.7 Scattering

6.7.4.2 EXTRINSIC ATTENUATION

It is loss due to external sources. Extrinsic attenuation may occur as –

Macrobending - The fibre is sharply bent so that the light travelling down the fibre

cannot make the turn & is lost in the cladding.

Micro bending - Micro bending or small bends in the fibre caused by crushing

contraction etc. These bends may not be visible with the naked eye.

Attenuation is measured in decibels (dB). A dB represents the comparison between the

transmitted and received power in a system.

6.7.5 BANDWIDTH

It is defined as the amount of information that a system can carry such that each pulse of

light is distinguishable by the receiver.

System bandwidth is measured in MHz or GHz. In general, when we say that a system has

bandwidth of 20 MHz, means that 20 million pulses of light per second will travel down the

fibre and each will be distinguishable by the receiver.

6.7.6 NUMBERICAL APERTURE

Numerical aperture (NA) is the "light - gathering ability" of a fibre. Light injected into the

fibre at angles greater than the critical angle will be propagated. The material NA relates to

the refractive indices of the core and cladding.

NA = n12 - n2

2

where n1 and n2 are refractive indices of core and cladding respectively.

In general, fibres with a high bandwidth have a lower NA. They thus allow fewer modes

means less dispersion and hence greater bandwidth. A large NA promotes more modal

dispersion, since more paths for the rays are provided NA, although it can be defined for a

single mode fibre, is essentially meaningless as a practical characteristic. NA in a multimode

fibre is important to system performance and to calculate anticipated performance.

Light

Ray

Light is lost

Light

Ray

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Numerical Aperture of fiber

* Light Ray A : Did not Enter Acceptance Cone - Lost

* Light Ray B : Entered Acceptance Cone - Transmitted through the Core by Total Internal

Reflection.

Figure-6.8- numerical aperture

6.8 OFC SPLICING

Splices are permanent connection between two fibres. The splicing involves cutting of the

edges of the two fibres to be spliced.

6.8.1 Splicing Methods

The following three types are widely used :

-Adhesive bonding or Glue splicing.

-Fusion splicing

6.8.2 Adhesive Bonding or Glue Splicing

This is the oldest splicing technique used in fibre splicing. After fibre end preparation, it is

axially aligned in a precision V–groove. Cylindrical rods or another kind of reference

surfaces are used for alignment. During the alignment of fibre end, a small amount of

adhesive or glue of same refractive index as the core material is set between and around the

fibre ends. A two component epoxy or an UV curable adhesive is used as the bonding agent.

6.8.3 Fusion Splicing

The fusion splicing technique is the most popular technique used for achieving very low

splice losses. The fusion can be achieved either through electrical arc or through gas flame.

The process involves cutting of the fibers and fixing them in micro–petitioners on the fusion

splicing machine. The fibers are then aligned either manually or automatically core aligning

(in case of S.M. fiber ) process

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7. MOBILE COMMUNICATION

A mobile phone uses radio wave signal for its connectivity with the subscriber.The

mobile phone works on the frequency signal and each mobile phone connection has its own

frequency. These frequencies are sending from the basic lower station tower. Each tower

has a range of 5 km in the city circle and there are a number of towers in the city to provide

connectivity to each mobile phone subscriber. The city is divided into imaginary hexagon

as its area plans out and each hexagon point has a tower for providing frequency signals to

the mobile subscriber. When the mobile sends signals to the base tower then it is called

uplink signal. When the base tower sends signal to the mobile then its downlink signals on

the highways the range of base tower of sending signal to the mobile phone subscribers is

25 km.

7.1 Basic terms in mobile communication are:-

-MSC: TAX for mobile phones

-HLR: Home Location Register

-TRC: Traffic Controller

-VLR: Visitors Location Register

-MNC: Mobile Network CodeBSC: Base Station Control

7.1.1 MSC:

It acts as a trunk automatic exchange (TAX). All the switching is done here in this TAX.

Each and every call made by the mobile subscribers is first collected from the base station

are send to the MSC where all the necessary verification of the subscriber is made and then

the switching of the call is made by the MSC. The OSS is a component within the MSC

which maintains the MSC. The functions of OSS are maintenance of MSC.

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Figure-7.2-MSC

7.1.2 HLR:

The Home Location Register stores each and every data of the mobile subscriber. Before

the call is switched for the mobile subscriber the MSC verifies the subscriber and all the

verification data is provided by the HLR. When the subscriber is on roaming facility, the

MSC of that area collects all the necessary information of the subscriber from its home MSC

through its HLR.

7.1.3 TRC:

The traffic controller controls the traffic for MSC and also controls the traffic of subscriber

trying to make contact with the MSC when call is made or received.

7.1.4 VLR:

The Visitor Location Register keeps a track record of subscribers who are on roaming

facility and all the records of the visitor coming from a different MSC area.

7.1.5 MNC:

Each and every country and its states have a unique Mobile Network Code (MNC) which

makes a difference between the mobile subscriber of two different countries and also within

the states. The MNC for India is 404and for Jharkhand BSNL mobile is INA76 where INA

refers to the Indian Network.

7.1.6 BSC:

The Base Station acts as important media for call transfer and call receiving for the mobile

subscribers. It sends frequency signals for the connectivity of mobile subscriber. The BSC

is connected to its towers through 2 MB link and is directly connected to the MSC where

all call switching takes place for the mobile subscribers. Each base station is provided 124

frequencies and a time slot of 8 channels for every call.

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Figure-7.3- ramp camp office

7.2 GSM Network Components

The GSM network is divided into two systems. Each of these systems is comprised of a

number of functional units which are individual components of the mobile network. The

two systems are:

Switching System (SS)

Base Station System (BSS)

GSM networks are operated, maintained and managed from computerized centers.

7.3 Subscriber Identity Module (SIM)

SIM card is the key feature of the GSM. It contains information about the subscriber and

must be plugged into the ME to enable the subscriber to use the network with the exception

of emergency calls MS can only be operated if a valid SIM is present.

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8. INTODUCTION TO GSM AND CDMA TECHNOLOGY

8.1 What is GSM?

If you are in Europe, Asia or Japan and using a mobile phone then most probably you

must be using GSM technology in your mobile phone.

GSM stands for Global System for Mobile Communication and is an open, digital

cellular technology used for transmitting mobile voice and data services.

The GSM emerged from the idea of cell-based mobile radio systems at Bell

Laboratories in the early 1970s.

The GSM is the name of a standardization group established in 1982 to create a

common European mobile telephone standard.

The GSM standard is the most widely accepted standard and is implemented

globally.

The GSM is a circuit-switched system that divides each 200kHz channel into eight

25kHz time-slots. GSM operates in the 900MHz and 1.8GHz bands in Europe and

the 1.9GHz and 850MHz bands in the US.

The GSM is owning a market share of more than 70 percent of the world's digital

cellular subscribers.

The GSM makes use of narrowband technique for transmitting signals.

The GSM was developed using digital technology. It has an ability to carry 64 kbps

to 120 Mbps of data rates.

Presently GSM support more than one billion mobile subscribers in more than 210

countries throughout of the world.

The GSM provides basic to advanced voice and data services including Roaming

service. Roaming is the ability to use your GSM phone number in another GSM

network.

A GSM digitizes and compresses data, then sends it down through a channel with two other

streams of user data, each in its own time slot. It operates at either the 900 MHz or 1,800

MHz frequency band.

Specifications for different Personal Communication Services (PCS) systems vary among

the different PCS networks. The GSM specification is listed below with important

characteristics.

8.2 Modulation:

Modulation is a form of change process where we change the input information into a

suitable format for the transmission medium. We also changed the information by

demodulating the signal at the receiving end.

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8.3 Access Methods:

Because radio spectrum is a limited resource shared by all users, a method must be devised

to divide up the bandwidth among as many users as possible.GSM chose a combination of

TDMA/FDMA as its method. The FDMA part involves the division by frequency of the

total 25 MHz bandwidth into 124 carrier frequencies of 200 kHz bandwidth. One or more

carrier frequencies are then assigned to each BS. Each of these carrier frequencies is then

divided in time, using a TDMA scheme, into eight time slots. One time slot is used for

transmission by the mobile and one for reception. They are separated in time so that the

mobile unit does not receive and transmit at the same time.

8.4 Transmission Rate:

The total symbol rate for GSM at 1 bit per symbol in GMSK produces 270.833 K

symbols/second. The gross transmission rate of the time slot is 22.8 Kbps. GSM is a digital

system with an over-the-air bit rate of 270 kbps.

8.5 Frequency Band:

The uplink frequency range specified for GSM is 933 - 960 MHz (basic 900 MHz band

only). The downlink frequency band 890 - 915 MHz (basic 900 MHz band only).

8.6 Speech Coding:

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.

8.7Access Network:

Access network, the network between local exchange and subscriber, in the Telecom

Network accounts for a major portion of resources both in terms of capital and manpower.

So far, the subscriber loop has remained in the domain of the copper cable providing cost

effective solution in past. Quick deployment of subscriber loop, coverage of inaccessible

and remote locations coupled with modern technology have led to the emergence of new

Access Technologies. The various technological options available are as follows :

-Multi Access Radio Relay

-Wireless In Local Loop

-Fibre In the Local Loop

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8.8 Wireless in Local Loop (WLL)

Fixed Wireless telephony in the subscriber access network also known as Wireless in Local

Loop (WLL) is one of the hottest emerging market segments in global telecommunications

today. WLL is generally used as “the last mile solution” to deliver basic phone service

expeditiously where none has existed before. Flexibility and expediency are becoming the

key driving factors behind the deployment of WILL.

WLL shall facilitate cordless telephony for residential as well as commercial complexes

where people are highly mobile. It is also used in remote areas where it is uneconomical to

lay cables and for rapid development of telephone services. The technology employed shall

depend upon various radio access techniques, like FDMA, TDMA and CDMA.

8.9 SPREAD SPECTRUM PRINCIPLE

Originally Spread spectrum radio technology was developed for military use to counter the

interference by hostile jamming. The broad spectrum of the transmitted signal gives rise to

“ Spread Spectrum”. A Spread Spectrum signal is generated by modulating the radio

frequency (RF) signal with a code consisting of different pseudo random binary sequences,

which is inherently resistant to noisy signal environment.

A number of Spread spectrum RF signals thus generated share the same frequency spectrum

and thus the entire bandwidth available in the band is used by each of the users using same

frequency at the same time.

FIGURE-8.1 SPREAD SPECTRUM PRINCIPLE

Frequency of operation: 824-849Mhz and 869-894 Mhz.

Duplexing Mehtod: Frequency Division Duplexing (FDD).

Access Channel per carrier: Maximum 61 Channels.

RF Spacing: 1.25 Mhz.

Coverage: 5 Km with hand held telephones and approx. 20 Km with fixed units.

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Hand Offs in CDMA

As the phone moves through a network the system controller transfers the call from one cell

to another, this process is called “handoff”. Handoffs maybe done with the assistance of the

mobile or the system controller will control the process by itself. Handoffs are necessary to

continue the call as the phone travels. Handoffs may also occur in idle state due to mobility.

Types of Handoffs in CDMA: There are primarily three types of Handoffs in CDMA. They

are

Soft

Hard and

Idle.

The type of handoff depends on the handoff situation.

To understand this we should know the cellular concept used in CDMA.

CDMA frequency- reuse planning (cellular concept):

Each BTS in a CDMA network can use all available frequencies. Adjacent cells can transmit

at the same frequency because users are separated by code channels, not frequency channels.

BTSs are separated by offsets in the short PN code This feature of CDMA, called "frequency

reuse of one," eliminates the need for frequency planning

Soft Handoff:

A soft handoff establishes a connection with the new BTS prior to breaking the connection

with the old one. This is possible because CDMA cells use the same frequency and because

the mobile uses a rake receiver. The CDMA mobile assists the network in the handoff. The

mobile detects a new pilot as it travels to the next coverage area. The new base station then

establishes a connection with the mobile. This new communication link is established while

the mobile maintains the link with the old BTS.

Soft handoffs are also called "make-before-break." Soft handoff can take place only when

the serving cell and target cell are working in the same frequency.

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9. INTRODUCTION TO INTERNET AND BROADBAND

9.1 INTERNET

The internet connection requires a computer which has Internet Explorer software

signal and analog signal to digital signal, a telephone line connection. The data is sent

through telephone line connection to the local exchange, from where it is then sent to the

main exchange.

The main exchange consists of a Node. The Node consists of a control card and a modem

from where it is sent to its main. Node is in the form of packets. It has two parts- LAN and

Control Card.

Figure-9.1 Internet networks

The main Node is connected to the main server which is located at New Delhi. From here it

is sent to gateway, which is connected to the World Wide Web (WWW)

Figure-9.2 web path

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9.2 INTERNET CONNECTIVITY

Telephone Local Exchange (through PCM) LAN

Control Card (routers, packet switching) Modem

WAN Patna (through OFC, B2 Node) Delhi

Network Connection Gateway

9.3 OVERVIEW OF BROAD BAND

Broadband is often called high-speed Internet, because it usually has a high rate of data

transmission. In general, any connection to the customer of 256 kbit/s or more is considered

broadband.

9.3.1 HOW IS BROADBAND DIFFERENT FROM DIAL-UP SERVICE?

Broadband service provides higher speed of data transmission—Allows more

content to be carried through the transmission “pipeline.”

Broadband provides access to the highest quality Internet services—streaming

media, VoIP (Internet phone), gaming and interactive services. Many of these

current and newly developing services require the transfer of large amounts of data

which may not be technically feasible with dial-up service. Therefore, broadband

service may be increasingly necessary to access the full range of services and

opportunities that the Internet can offer.

Broadband is always on—does not block phone lines and no need to reconnect to

network after logging off.

9.3.2 What is Broadband Service?

Broadband refers to a connection that has capacity to transmit large amount of data at high

speed. Presently a connection having download speeds of 256 kbps or more is classified as

broadband. When connected to the Internet broadband connection allows surfing or

downloading much faster than a dial-up or any other narrowband connections. BSNL offers

2 Mbps minimum download speed for its Broadband connections.

Requirement for providing Broad Band connection:

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Personal Computer

ADSL Modem

Land Line Connection

Splitter for separating telephone from Personal computer.

9.3.3 Services available through Broadband

High speed Internet Access: This is the always-on Internet access service with speed

ranging from 256 kbps to 8 Mbps.

Bandwidth on Demand: This will facilitate customer to change bandwidth as per his /

her requirement. For example a customer with 256 kbps can change to 1 Mbps during

the video Conferencing session.

Multicasting: This is to provide video multicast services, video-on-demand etc. for

application in distance education, telemedicine etc.

Dial VPN Service: This service allows remote users to access their private network

securely over the NIB-II infrastructure.

Video and Audio Conferencing:

Content based Services: Like Video on Demand, Interactive Gaming, Live and time

shifted TV

Video on Demand: Customers can view any movie of their choice from a pool of

movies stored in a central server. The movies can be viewed either on a TV or a PC.

Audio on Demand: It is a similar service where person can listen to any music of his

choice.

TV channels through broadband connection: The TV channels may be available in

the broadband connection. In fact, there may be other new channels, particularly the

educational and scientific channels, depending on demand. Additional equipments

required in the customer's premises are

Set Top Box (STB) - The STB converts the digital IP based signal to a form

compatible with the TV set.

PC and TV

The TV services envisaged are:

i. S-VoD : Subscription based Video Content, as in Pay Channels.

ii. Video-On-Demand

iii. N-VoD : Near Video-On-Demand. NVOD provides playouts on

fixed time bands which people can watch against payment.

iv. T-VOD : Transaction or Pay-Per-View service.

The video content will have Hindi, international and regional movies, music, soaps

and serials, sports, news, interactive gaming, e-learning and niche channels. "The

driver in entertainment will be on-demand movies, interactive gaming, broadband

Internet connectivity and e-learning,"

Billing: To provide a means to bill for the aforesaid services by either time-based or

volume-based billing. It shall provide the customer with the option to select the

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services through web server To provide both pre-paid and post paid broadband

services

IP Telephony

Messaging: plain and feature rich,

Multi-site MPLS VPN with Quality of Service (QoS) guarantees.

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10. CONCLUSION

The working in the project was an interesting and an all together learning experience.

New technologies, new progress and new competition are the order of the day. The core

area to look for is highly fragmented and information intense activity sequence that involves

a number of player and audiences.

The project mainly revolves around: EWSD, TAX, internet node, mobile communication,

WLL and intelligence network.

The emphasis of the different parts of the project is to throw light on the systems working

in Patna Main Exchange. The project also deals with modern technologies attributes and

the scope of implementation of the same in Patna. The area under study was limited to Patna

Main Exchange.

The scope of the study is very vast and the topic under study deals with the volatile

technology world. After the study, suggestions and strategy has been formulated keeping in

view the limitations of the field.

Evolution of this technological world is occurring every minute. Thanks to telecom and web

technologies, countries are coming closer day by day.

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11. REFERENCES

This report has been compiled with valuable contribution from:

BOOKS:

Training Notes provided by Mr. Anand Prakash Singh (SDE), BSNL, PATNA.

WEB RESOURCES:

www.electronics4u.com

www.projectsguide.com

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