This document is an inplant training report submitted by Aswinkumar.R during his training at BSNL in Chennai from July 24th to August 7th 2014. It includes sections on the company profile of BSNL, an introduction to telecommunication technologies used including exchanges, local and trunk lines, PCM, fibre optics and mobile communication technologies like GSM and CDMA. It provides a high-level overview of the technologies and systems used at BSNL for telecom services.

1. INPLANT TRAINING
AT
BSNL,CHENNAI
BY:
ASWINKUMAR.R
ECE 3RD YEAR

2. Inplant Training Report
Submitted By
ASWINKUMAR.R
In partial fulfillment
Of
Bachelor of Technology
In
Electronics and Communication Engineering
From 24/07/2014 to 07/08/2014

3. ACKNOWLEDGEMENT
It gives us immense pleasure to express ours profound gratitude to ours bonafide
University, Srm University to encourage students to undergo summer training to gain
valuable practical experiences from various industries and companies. We extend my
thanks to SDE in charge of training Mrs. Meenakshi, who encouraged us to undergo this
inplant training at BSNL’s Advanced Training Centre, chennai.
We also extend my thanks to all the faculties and teaching staff at BSNL for their
invaluable support and assistance.
Lastly we would like to thank all the employees/respondents of BSNL, chennai.
Aswinkumar.R.

4. CONTENT
COMPANY PROFILE
INTRODUCTION
ABOUT THE EXCHANGE
LOCAL AND TRUNK LINE
PCM
FIBRE OPTICS COMMUNICATION
OVERVIEW OF MOBILE COMMUNICATION
GSM TECHNOLOGY
CDMA TECHNOLOGY
INTRODUCTION TO INTERNET AND BROADBAND
CONCLUSION

5. 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.

6. 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.
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.
 1979 - First optical fibre system for local junction commissioned at pune

7.  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
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.
 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).

8. 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.
TYPE’S OF EXCHANGE
 Manual exchange
 Strowger exchange
 Cross bar exchange
 Electronics exchange (analog and digital exchange)
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.
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.
Diagram of a simple Selector

9. In Figure 2 (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 3, below.
A Two-Motion "Final" Selector
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.
CROSS BAR EXCAHNGE
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.

10. 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.
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 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.
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 rate. 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.

11. 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
1) TERMINATION CARD
2) SERVICE CARD
3) CONTROL CARD
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
Service card: the service like dial tone ,call waiting ,call confrencing etc is given
by this card.
Control card: it is there to see whether the call has been established or not. If
established then requisite unit has been established or not.
Local and trunk Network
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

12. 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 of light--though that has rarely stopped
uneducated IT or IS managers from demanding that cabling perform faster instead of upgrading
equipment.
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.
What is Trunking?
In telecommunications systems, trunking is the aggregation of multiple user circuits into a single
channel. The aggregation is achieved using some form of multiplexing.
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

13. 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.
Basic Requirements for PCM System:
To develop a PCM signal from several analogue signals, the following processing steps are
required:
1. Filtering
2. Sampling
3. Quantisation
4. Encoding
5. Line Coding
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:
1. Frequency Division Duplexing (FDD)
2. Time Division Duplexing (TDD)

14. 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.
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 phones.
FIBER-OPTICS COMMUNICATION
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.
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.

15. • RESISTANCE: Greater resistance to electromagnetic noise such as radios, motors or other
nearby cables.
• MAINTENANCE: Fiber optic cables costs much less to maintain.
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 :
(1) Information is Encoded into Electrical Signals.
(2) Electrical Signals are Coverted into light Signals.
(3) Light Travels Down the Fiber.
(4) A Detector Changes the Light Signals into Electrical Signals.
(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.
Principle of Operation - Theory
 Total Internal Reflection - The Reflection that Occurs when a Ligh Ray Travelling in
One Material Hits a Different Material and Reflects Back into the Original Material
without any Loss of Light.

16. PROPAGATION OF LIGHT THROUGH FIBER
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.
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
50m and a cladding diameter of 125m.

17. 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)
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.
STEP-INDEX MULTIMODE FIBER
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.
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 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.

18. 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.
SINGLE-MODE FIBER
OPTICAL FIBRE PARAMETERS
Optical fiber systems have the following parameters.
(I) Wavelength.
(II) Frequency.
(III) Window.
(IV) Attenuation.
(V) Dispersion.
(VI) Bandwidth.
9.1 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.
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.
WINDOW
A narrow window is defined as the range of wavelengths at which a fibre best operates.
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.
INTRINSIC ATTENUATION
It is loss due to inherent or within the fibre. Intrinsic attenuation may occur as
(1) Absorption - Natural Impurities in the glass absorb light energy.
Light
Ray

19. (2) Scattering - Light Rays Travelling in the Core Reflect from small Imperfections into a
New Pathway that may be Lost through the cladding.
Light
Ray
Light is lost
Fig. 10 Scattering
EXTRINSIC ATTENUATION
It is loss due to external sources. Extrinsic attenuation may occur as –
(I) Macrobending - The fibre is sharply bent so that the light travelling down the fibre
cannot make the turn & is lost in the cladding.
Micro and Macro bending
(II) 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.
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.
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 = n1
2 - n2
2
where n1 and n2 are refractive indices of core and cladding respectively.

20. 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.
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.
OFC Splicing
Splices are permanent connection between two fibres. The splicing involves cutting of the edges
of the two fibres to be spliced.
Splicing Methods
The following three types are widely used :
1. Adhesive bonding or Glue splicing.
2. Fusion splicing
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.
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. Afterwards the operation that takes place involve withdrawal of the
fibers to a specified distance, preheating of the fiber ends through electric arc and bringing
together of the fiber ends in a position and splicing through high temperature fusion

21. MOBILE COMMUNICATION
A mobile phone uses radio wave signal for its connectivity with the subscriber.
Mobile Phone Towers
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.
Basic terms in mobile communication are:-
1. MSC: TAX for mobile phones
2. HLR: Home Location Register
3. TRC: Traffic Controller
4. VLR: Visitors Location Register
5. MNC: Mobile Network Code
6. BSC: Base Station Control
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

22. 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.
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.
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.
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.
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.
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.

23. 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.
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.
These store three types of subscriber related information:
1. Fixed data stored before the subscription is sold such as authentication key and security
algorithms.
2. Temporary network data such as the location area of the subscriber and forbidden
PLMNS.
3. Service data such as language preference advice of charge.
There are two types of SIM cards:-
ID-SIM: The format and layout of the ID-SIM complies with ISO standards for integrated circuit
cards.
PLUG-In SIM: The plug-in SIM is smaller than the ID-SIM and is intended for semi permanent
installation in the MNS.

24. INTODUCTION TO GSM TECHNOLOGY
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.
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.
The GSM uses Gaussian Minimum Shift Keying (GMSK) modulation method.

25. 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.
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.
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).
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.
Access 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 :
1. Multi Access Radio Relay
2. Wireless In Local Loop
3. Fibre In the Local Loop

26. Wireless in Local Loop (WILL)
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.
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.
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.

27. 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.

28. INTRODUCTION TO INTERNET AND BROADBAND
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.
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)

29. INTERNET CONNECTIVITY
Telephone Local Exchange (through PCM) LAN
Control Card (routers, packet switching) Modem
WAN Patna (through OFC, B2 Node) Delhi
Network Connection Gateway
OVERVIEW OF BROAD BAND
Definition 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.

30. 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.
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
 Personal Computer
 ADSL Modem
 Land Line Connection
 Splitter for separating telephone from Personal computer.
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.

31.  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
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.
 Wi-Fi
 Web hosting & web co-location.
 Lease line service.

32. 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 nagpur. The area under study was limited to nagpur 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.