Summar Training on BSNL

1. APEX INSTITUTE OF TECHNOLOGY
Affiliated by AKTU (Formally UPTU), Lucknow,
College Code-280, Kaushalganj, Rampur, UP (India)
2016-2017
TRAINING REPORT
On
Submitted for partial fulfilment of award of
BACHELOR OF TECHNOLOGY
Degree
In
DEPARTMENT OF ELECTRONICS AND
COMMUNICATION ENGINEERING
Submitted to:
Mrs. Pratima Verma
(Assistant Professor)
(ECE, Dept)
Submitted By:
Amit Kirti Saran
1328031002
ECE, 4th
year

2. ACKNOWLEDGEMENT
It gives us immense pleasure to express ours profound gratitude to ours bonafide University,
Dr. APJ Abdul Kalam University (formally UPTU) 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 Mr. S. SONI (SDE) & Mr.
Jaswant Singh (JTO), who encouraged us to undergo this implant training at BSNL’s
Training Centre, Rampur.
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, Rampur.
Amit Kirti Saran.

3. APEX INSTITUTE OF TECHNOLOGY
Affiliated by AKTU (Formally UPTU), Lucknow,
College Code-280, Kaushalganj, Rampur, UP (India)
2016-2017
ABSTRACT
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.
Since time immemorial, a man has tried hard to bring the world as close to himself as
possible. His thirst for information is hard to quench so he has continuously tried to develop
new technologies, which have helped to reach the objective.
The world we see today is a result of the continuous research in the field of communication,
which started with the invention of telephone by Graham Bell to the current avatar as we see
in the form INTERNET and mobile phones. All these technologies have come to existence
because man continued its endeavour towards the objective.
This project report of mine has been a small effort in reviewing the trends technologies
prevailing, Spending a period of four weeks with Telecommunication Networking. The report
on how the BSNL Basic Telecom Network work and how to exchange work and how the
company work with telecommunication Network.

4. TABLE OF CONTENTS
CHAPTER NO. TITLE PAGE NO.
TITLE…………………………………………………………………………………………………………………………………………..i
CERTIFICATE………………………………………………………………………………………………………………………………ii
ACKNOWLEDGEMENT……………………………………………………………………………………………………………….iii
ABSTRACT…………………………………………………………………………………………………………………………………iv
TABLE OF CONTENT……………………………………………………………………………………………………………………v
LIST OF FIGURE……………………………………………………………………………………………………………………………vi
CHAPTER 01…………………………………………………………………………………………………………………………………1
1.1 Introduction………………………………………………………………………………………………………………….1
1.2 Profile……………………………………………………………………………………………………………………………2
CHAPTER 02…………………………………………………………………………………………………………………………………4
2.1 About the exchange………………………………………………………………………………………………………4
2.1.1 Type of Exchange……………………………………………………………………………………………………4
CHAPTER 03…………………………………………………………………………………………………………………………………8
3.1 DIGITAL CARD………………………………………………………………………………………………………………8
CHAPTER 04……………………………………………………………………………………………………………………………….10
4.1 PCM……………………………………………………………………………………………………………………………10
CHAPTER 05………………………………………………………………………………………………………………………………12
5.1 Fiber-Optics Communication……………………………………………………………………………………….12
CHAPTER 06………………………………………………………………………………………………………………………………19
6.1 Mobile Communication………………………………………………………………………………………………19
CHAPTER 07………………………………………………………………………………………………………………………………22
7.1 Introduction of GSM Technology…………………………………………………………………………………22
CHAPTER 08………………………………………………………………………………………………………………………………25
8.1 Spread Spectrum Principle…………………………………………………………………………………………..25
CHAPTER 09………………………………………………………………………………………………………………………………27
9.1 Introduction of Internet and Broadband…………………………………………………………………….27
CONCLUSION……………………………………………………………………………………………………………………………31

5. 1
CHAPTER 1
1.1 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
 1980 - First satellite earth station for domestic communications established
at scikandarabad.

6. 2
 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).
1.1PROFILE
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.

7. 3
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.

8. 4
CHAPTER 2
2.1 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.
2.1.1 TYPE’S OF EXCHANGE
1 Manual exchange
2 Strowger exchange
3 Cross bar exchange
4 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.
Figure 2.1 Diagram of a simple Selector

9. 5
In Figure 2.1 (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 3, below.
Figure 2.2 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.

10. 6
 CROSS BAR EXCAHNGE
In , a crossbar switch (also known as cross-point switch, cross-point 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.
 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 analogy electronics exchange and time division switching is used for digital
exchange.
Figure 2.3 Telephone C-DOT Electronics 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

11. 7
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.

12. 8
CHAPTER 3
3.1DIGITAL 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 conferencing 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 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

13. 9
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.

14. 10
CHAPTER 4
4.1 PULSE CODE MODULATION (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.
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)
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

15. 11
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.
Time division multiplexing is used at local exchanges to combine a number of incoming voice
signals onto an outgoing trunk. Each incoming channel is allocated a specific time slot on the
outgoing trunk, and has full access to the transmission line only during its particular time slot.
Because the incoming signals are analogue, they must first be digitised, because TDM can only
handle digital signals. Because PCM samples the incoming signals 8000 times per second, each
sample occupies 1/8000 seconds (125 µseconds). PCM is at the heart of the modern
telephone system, and consequently, nearly all time intervals used in the telephone system
are multiples of 125 µseconds.
Because of a failure to agree on an international standard for digital transmission, the systems
used in Europe and North America are different. The North American standard is based on a
24-channel PCM system, whereas the European system is based on 30/32 channels. This
system contains 30 speech channels, a synchronisation channel and a signalling channel, and
the gross line bit rate of the system is 2.048 Mbps (32 x 64 Kbps). The system can be adapted
for common channel signalling, providing 31 data channels and employing a single
synchronisation channel. The following details refer to the European system.
The 30/32 channel system uses a frame and multi frame structure, with each frame consisting
of 32 pulse channel time slots numbered 0-31. Slot 0 contains the Frame Alignment Word
(FAW) and Frame Service Word (FSW). Slots 1-15 and 17-31 are used for digitised speech
(channels 1-15 and 16-30 respectively). In each digitised speech channel, the first bit is used
to signify the polarity of the sample, and the remaining bits represent the amplitude of the
sample. The duration of each bit on a PCM system is 488 nanoseconds (ns). Each time slot is
therefore 3.904 µseconds (8 bits x 488 ns). Each frame therefore occupies 125 milliseconds
(32 x 3.904 ms).
In order for signalling information (dial pulses) for all 30 channels to be transmitted, the multi
frame consists of 16 frames numbered 0-15. In frame 0, slot 16 contains the Multi frame
Alignment Word (MFAW) and Multi frame Service Word (MFSW). In frames 1-15, slot 16
contains signalling information for two channels. The frame and multi frame structure are
shown below. The duration of each multi frame is 2 milliseconds(125 µseconds x 16).
Figure 4.1 The frame and multi frame structures for a 30/32 channel PCM system

16. 12
CHAPTER 5
5.1 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 :
Fibre 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.
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.

17. 13
(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.
Figure 5.1 transmission System
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.
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

18. 14
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 5.2 Cladding index
50m and a cladding diameter of 125m.
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
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

19. 15
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.
Figure 5.3 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.
Figure 5.4 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.
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 5.5 Single-mode fiber

20. 16
OPTICAL FIBRE PARAMETERS
Optical fiber systems have the following parameters.
(I) Wavelength.
(II) Frequency.
(III) Window.
(IV) Attenuation.
(V) Dispersion.
(VI) Bandwidth.
 WAVE LENGTH
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.
(2) Scattering - Light Rays Travelling in the Core Reflect from small Imperfections into a
New Pathway that may be Lost through the cladding.
Fig. 5.6 Scattering
Light
Ray
Light is lost

21. 17
 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.
Figure 5.7 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
Micro bend
Micro bend
Fig. Loss and Bends
Micro bend

22. 18
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.
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
Figure 5.8 Aperture of fiber
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.

23. 19
CHAPTER 6
6.1MOBILE COMMUNICATION
A mobile phone uses radio wave signal for its connectivity with the subscriber.
Mobile Phone Towers
Figure 6.1 Ya-uda antenna
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 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.

24. 20
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.

25. 21
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.

26. 22
CHAPTER 7
7.1 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.

27. 23
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
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

28. 24
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.

29. 25
CHAPTER 8
8.1SPREAD 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 transmission and Receiver System
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.
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):

30. 26
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.

31. 27
CHAPTER 9
9.1INTRODUCTION 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.
Figure 9.1 Setup connection
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 Systematic flow of connectivity

32. 28
Data Terminal
Modem
Telephone line
Exchange
Internet Gateway
Figure 9.3 Flow diagram of internet Connectivity
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.
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.”

33. 29
 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.
 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.

34. 30
 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.

35. 31
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.