Indian Railway is the state-owned railway company of India, which owns and operates most of the country's rail transport. It is overseen by the Ministry of Railways of the Government of India It's provides the full knowledge about Indian railways & its signalling system and it's gives the knowledge about rail-net and the network used in Indian rail and the topology used in indian railway for the internet .

1. A
REPORT
ON
INDUSTRIALTRAINING
IN
SIGNAL AND TELECOMMUNICATION ENGINEERING
DIVISIONAL RAILWAY MANAGER OFFICE, NEW DELHI
SUBMITTED IN PARTIAL FULFILLMENT OF THE REQUIREMENT
FOR THE AWARD OF THE DEGREE OF
BACHELOR OF TECHNOLOGY
IN
Electronics & Communication Engineering
Submitted By
Ramakant Tyagi
1219431055

2. DECLARATION
I hereby declare that all the work presented in this report in the partial fulfillment
of the requirement for the award of the degree of Bachelor of Technology in
Electronics & communication Engineering, H.R Institute of Technology UPTU U.P,
is an authentic record of the workdone during the IndustrialInternship carried out
in Northern Railway under the guidance of
Date:
Signature

3. ACKNOWLEDGEMENT
I am very much gratefulto the authorityof the organization for taking initiative for
the industrial training to upgrademyknowledge by placing me at Northern
Railway. I owe many thanks to several people who helped and supported me
during this training.
I wish to express my gratitude to the officials and other members of Northern
Railway who rendered their help during the period of my training.
I express my sincere thanks to senior section engineer, who through her expert
guidance helped me throughout the course of this training. If it was not her
motivation and encouragement, I would nothave seen through this training course
in an honest course to the splendor of success.
Ramakant Tyagi
(Electronics & Communication
Engineering)
H.RInstitute of Technology

4. ABSTRACT
This report takes a pedagogical stance in demonstrating how results from
theoretical computer science may be applied to yield significant insight into the
behavior of the devices computer systems engineering practice seeks to put in
place, and that this is immediately attainable with the present state of the art.
The focus for this detailed study is provided by the type of solid state
signaling and various communication systems currently being deployed
throughout mainline railways. Safety and system reliability concerns dominate in
this domain. With such motivation, two issues are tackled: the special problem of
software quality assurance in these data-driven control systems, and the broader
problem of design dependability. In the former case, the analysis is directed
towards proving safety properties of the geographic data which encode the
control logic for the railway interlocking; the latter examines the fidelity of the
communication protocols upon which the distributed control system depends.

5. TABLE OF CONTENTS
 CHAPTER 1: INTRODUCTION
1.1 ABOUT INDIAN RAILWAYS
1.2 GENESIS OF INDIAN RAILWAYS
1.3 OTHER MILESTONES
1.4 THE NEED FOR A RAILWAY NETWORK
1.5 RECENT DEVELOPMENTS
 CHAPTER 2: OPTICAL FIBRE COMMUNICATION
SYSTEM
2.1 OPTICAL FIBER
2.2 FIBER GEOMETRY PARAMETERS
2.3 OPTICAL FIBRE COMMUNICATION
2.4 PULSE CODE MODULATION
2.5 MULTIPLEXING
2.6 FIBER OPTIC SOURCES
2.7 FIBER OPTIC DETECTORS
2.8 OPTICAL NETWORK CONFIGURATION
2.9 NETWORK ARCHITECTURE
 CHAPTER 3: RAILNET
3.1 INTRODUCTION
3.2 OBJECTIVES
3.3 RAILNET GENERAL ARRANGEMENT
3.4 THE RAILNET WORK
3.5 NETWORK TOPOLOGY
3.6 CATEGORIES OF NETWORK

6.  CHAPTER 4 : PRS & UTS Network
4.1 INTRODUCTION
4.2 INTERCONNECTION OF PRS & UTS SERVERS
4.3 PREVIOUS SET UP AT PRS/DELHI
4.4 CONCERT APPLICATION ARCHITECTURE
4.5 OTHER ASPECTS OF PRS
4.6 BENIFITS OF PRS
4.7 TECHNOLOGY USED
4.8 FUTURE ENHANCEMENTS
 CHAPTER 5 :EXCHANGE
5.1 INTRODUCTION
5.2 POWER SUPPLY UNIT CARD
5.3 RAX CONTROL PROCESSOR(RCP)
5.4 SWITCHING NETWORK(TIC)
5.5 TONE GENERATOR WITH DIAGNOSTIC CARD(TGS)
5.6 SIGNAL PROCESSOR (SP) CARD
5.7 SUBSCRIBER LINE CARD(SLC) OR LINE CIRCUIT CARD(LCC)
6: CONCLUTION

7. 1. INDIAN RAILWAY
INTRODUCTION
Indian Railway is the state-owned railway company of India, which owns and
operates most of the country's rail transport. It is overseen by the Ministry
of Railways of the Government of India.
Indian Railways has one of the largest and busiestrail networks in the world,
transporting over 18 million passengers and morethan 2 million tons of freight
daily. Itis the world's largestcommercial or utility employer, with more than
1.4 million employees. The railways traversethelength and breadth of the
country, covering 6,909 stations over a total route length of more than
63,327 kilometers (39,350 mi). As to rolling stock, IRowns over 200,000 (freight)
wagons, 50,000 coaches and 8,000 locomotives.
By 1947, theyear of India's independence, there were forty-two railsystems. In
1951 the systems werenationalized as one unit, becoming one of the largest
networks in the world. IRoperates both long distance and suburban railsystems
on a multi-gauge network of broad, metre and narrow gauges. Italso owns
locomotive and coach production facilities.

8. 1.1 About Indian Railways
Indian Railways, a historical legacy, are a vital force in our economy. The first railway on
Indian sub-continent ran from Bombay to Thane on 16th April 1853. Fourteen railway carriages
carried about 400 guests from Bombay to Thane covering a distance of 21 miles (34 Kilometers).
Since then there has been no looking back. Today, it covers 6,909 stations over a total route
length of more than 63,028 kilometers. The track kilometers in broad gauge (1676 mm) are 86,
526 kms, meter gauge (1000 mm) are 18, 529 kms and narrow gauge (762/610 mm) are 3,651
kms. Of the total route of 63,028 kms, 16,001 kms are electrified. The railways have 8000
locomotives, 50,000 coaching vehicles, 222,147 freight wagons, 6853 stations, 300 yards, 2300
goodsheds, 700 repair shops, and 1.54 million work force. Indian Railways runs around 11,000
trains every day, of which 7,000 are passenger trains. Presently, 9 pairs of Rajdhani and 13 pairs
of Shatabdi Express Trains run on the rail tracks of India.
It is interesting to note that though the railways were introduced to facilitate the
commercial interest of the British, it played an important role in unifying the country. Railways
are ideally suited for long distance travel and movement of bulk commodities. Regarded better
than road transport in terms of energy efficiency, land use, environment impact and safety it is
always in forefront during national emergency.
Indian railways, the largest rail network in Asia and the world's second largest under one
management are also credited with having a multi gauge and multi traction system. The Indian
Railways have been a great integrating force for more than 150 years. It has helped the economic
life of the country and helped in accelerating the development of industry and agriculture. Indian
Railways is known to be the largest railway network in Asia.
The Indian Railways network binds the social, cultural and economic fabric of the
country and covers the whole of country ranging from north to south and east to west removing
the distance barrier for its people. The railway network of India has brought together the whole
of country hence creating a feeling of unity among Indians.

9. 1.1.1 OrganizationOverview
The Ministry of Railways under Government of India controls Indian Railways. The
Ministry is headed by Union Minister who is generally supported by a Minster of State. The
Railway Board consisting of six members and a chairman reports to this top hierarchy. The
railway zones are headed by their respective General Managers who in turn report to the Railway
Board. For administrative convenience Indian Railways is primarily divided into 16 zones:
1.1.2 The Ministry of Railways has following nine undertakings:
1. Rail India Technical & Economic Services Limited (RITES)
2. Indian Railway Construction (IRCON) International Limited

10. 3. Indian Railway Finance Corporation Limited (IRFC)
4. Container Corporation of India Limited (CONCOR)
5. Konkan Railway Corporation Limited (KRCL)
6. Indian Railway Catering & Tourism Corporation Ltd (IRCTC)
7. Railtel Corporation of India Ltd. (Rail Tel)
8. Mumbai Rail Vikas Nigam Ltd. (MRVNL)
9. Rail Vikas Nigam Ltd. (RVNL)
Indian Railways have their research and development wing in the form of Research,
Designs and Standard Organization (RDSO). RDSO functions as the technical advisor and
consultant to the Ministry, Zonal Railways and Production Units.
1.1.3 RailwayBudget
Since 1924-25, railway finances have been separated from General Revenue. Indian
railways have their own funds in the form of Railway Budget presented to the Parliament
annually. This budget is presented to the Parliament by the Union Railway Minster two days
prior to the General Budget, usually around 26th February. It has to be passed by a simple
majority in the Lok Sabha before it gets final acceptance. Indian Railways are subject to the
same audit control as other government revenues and expenditure.
1.1.4 PassengerTraffic
The passenger traffic has risen from leaps and bounds from 1284 million in 1950-51 to
5112 million in 2002-2003.
1.1.5 FreightTraffic
The revenue fright traffic has also grown immensely from 73.2 million tons in 1950-51 to
557.39 million tones. Indian railways carry huge variety of goods such as mineral ores,
fertilizers, petrochemicals, agricultural produce and others. It has been made possible with

11. measures such as line capacity augmentation on certain critical sectors and modernization of
signaling system and increase in roller bearing equipped wagons. Indian Railways make huge
revenue and most of its profits are from the freight sector and uses these profits to augment the
loss-making passenger sector.
Here, it is important to note that computerization of freight operations --- Freight
Operations Information System (FOIS) has been achieved with the implementation of Rake
Management System.
1.1.6 Facilities forPassengers
Computer based unreserved ticketing takes care of the large chunk of unreserved segment
of passengers. This facility allows issuance of unreserved tickets from locations other than
boarding station.
1.1.7 Indian RailwayCatering and Tourism Corporation(IRCTC):
IRCTC has launched on line ticketing facility with the aid of Center for Railway
Information System, which can be booked on www.irctc.co.in. For the convenience of customers
queries related to accommodation availability, passenger status, train schedule etc are can all be
addressed online. Computerized reservation facilities have made the life easy of commuters
across India.
National Train Enquiry system is another initiative of Indian Railways which offers train
running position on a current basis through various output devices such as terminals in the
station enquiries and Interactive Voice Response Systems (IVRS) at important railway stations.
Indian Railways are committed to provide improved telecommunication system to its
passengers. For this Optical Fibre Communication (OFC) system has been embraced, which
involves laying optical fibre cable along the railway tracks. In recent years Indian Railways have
witnessed the marked rise of collaboration between private and public sectors. Few of the
notable examples here are the broad gauge connectivity to Pipya Port where a joint venture
company is formed with Pipava Port authority. Similarly Memorandums of Understanding has

12. been signed between Railways and State governments of Andhra Pradesh, Karnataka,
Maharashtra, West Bengal, Tamil Nadu and Jharkhand,
1.1.8 Rolling Stock
Today, Indian Railways have become self-reliant in production of rolling stock. It
supplies rolling stock to other countries and non-railway customers. The production units are at
Diesel Locomotive Works, Varanasi, Chittaranjan Locomotive Works, Chittaranjan, Diesel-Loco
Modernisation Works, Patiala, Integral Coach Factory, Chennai, Rail Coach Factory, Kapurthala,
Wheel & Axle Plant, Bangalore and Rail Spring Karkhana, Gwalior.
1.2 GENESIS OF INDIAN RAILWAYS
The story of the Indian Railways (IR) is not just a saga of mundane statistics and miles of
rolling stock. It is the glorious tale of a pioneering institution that has blazed a trail for nearly a
century and a half, making inroads into far-flung territory and providing a means of
communication.
Indian Railway is one of India's most effective networks that keep together the social,
economic, political and cultural fabric of the country intact. Be it cold, mountainous terrain or
the long stretches through the Rajasthan desert, Indian Railways cover the vast expanse of the
country from north to south, east to west and all in between.
More than a hundred years ago, on the 16 April 1853, a red-letter day appeared in the
glorious history of the Indian Railways. On the day, the very first railway train in India ran over
a stretch of 21 miles from Bombay to Thane. This pioneer railway train consisting of 14 railway
carriages carrying about 400 guests, steamed off at 3:30 pm amidst the loud applause of a vast
multitude and to the salute of 21 guns. It reached Thane at about 4.45 pm. The guests returned to
Bombay at 7 pm on the next day, that is, April 17. On April 18, 1853, Sir Jamsetjee Jeejeebhoy,
Second Baronet, reserved the whole train and traveled from Bombay to Thane and back along
with some members of his family and friends. This was the humble beginning of the modern
Indian Railway system known today for its extraordinary integration of high administrative

13. efficiency, technical skill, commercial enterprise and resourcefulness. Today the Indian Railway
(IR) is one of the most specialized industries of the world.
1.3 OTHER MILESTONES
Under the British East India Company's auspices, the Great Indian Peninsula Railway
Company (GIPRC) was formed on July 15, 1844. Events moved at a fast pace. On October 31, 1850,
the ceremony of turning the first sod for the GIPRC from Bombay to Kalyan was performed. The
opening ceremony of the extension to Kalyan took place on May 1, 1854. The railway line from
Kalyan to Khopoli was opened on May 12, 1856. It was further extended to Poona on June 14, 1858
when the traffic was opened for public use. In the eastern part of India, the first passenger train
steamed out of Howrah station for Hooghly, a distance of 24 miles, on August 15, 1854. This marked
the formation of the East Indian Railway.
This was followed by the emergence for the Central Bengal Railway Company. These small
beginnings multiplied and by 1880, the IR system had a route mileage of 9,000 miles in India. The
Northeastern Railway also developed rapidly. On October 19, 1875, the train between Hathras Road
and Mathura Cantonment was started. By the winter of 1880-81, the Kanpur-Farukhabad line became
operational and further east, the Dibrugarh-Dinjan line became operational on August 15, 1882. In
South India, the Madras Railway Company opened the first railway line between Veyasarpaudy and
the Walajah Road (Arcot) on July 1, 1856. This 63-mile line was the first section, which eventually
joined Madras and the west coast. On March 3, 1859, a length of 119 miles was laid from Allahabad
to Kanpur.
In 1862, the railway line between Amritsar and Attari was constructed on the Amritsar-
Lahore route. Some of the trains started by the British are still in existence. The Frontier Mail is one
such train. It was started on September 1, 1928 as a replacement for the Mumbai-Peshawar mail. It
became one of the fastest trains in India at that time and its reputation in London was very high. The
Kalka Mail from Howrah to Kalka was introduced with the specific goal of facilitating the annual
migration of British officials, their families and their retinue of servants and clerks from the imperial
capital at Calcutta to the summer capital in Shimla. From Kalka, there was the remarkable toy train
service to Shimla. Plans for this narrow-gauge train had started as early as 1847, but it was at the
intervention of the Viceroy, Lord Curzon, that work actually began. Hence this train service was also
known as the Viceroy's Toy Train. In order to prevent any head-on collisions on the single-track

14. sections of this railway service, the Neals Token System has been used ever since the train was
inaugurated. The train guards exchange pouches containing small brass discs with staff on the
stations en route. The train driver then puts these discs into special machines, which alert the signals
ahead of their approach. The Darjeeling toy trains, the Matheran toy train from Neral to Matheran,
the Nilgiri Blue Mountain Railway are other engineering marvels running on routes designed and
built by the British. Trains like the Deccan Queen from Bombay to Secunderabad and the Grand
Trunk Express from Delhi to Madras are some other prominent trains initiated by the British. With
the advancement in the railway system, electrifying railway lines began side by side, and it was in
1925, that the first electric train ran over a distance of 16 km from Victoria Terminus to Kurala.
1.4 THE NEED FOR A RAILWAY NETWORK
The British rule in India was governed by three principal considerations to expand the IR
system. These were the commercial advantages, the political aspect and even more importantly,
the inexorable imperial defense of India against the possible military attacks from certain
powerful countries showing signs of extending their orbit of influence into Central Asia.
1.5 RECENT DEVELOPMENTS
Now, to further improve upon its services, the Indian Railways have embarked upon
various schemes, which are immensely ambitious. The railway has changed from meter gauge to
broad gauge and the people have given it a warm welcome. Now, there are the impressive-
looking locomotives that haul the 21st-century harbingers-the Rajdhanis and Shatabdis-at speeds
of 145 kmph with all amenities and comfort. With these, the inconvenience of changing to a
different gauge en route to a destination will no longer be felt. The Research, Designing, and
Standardizing Organization at Lucknow-the largest railway research organization in the world-
was constituted in 1957. It is constantly devising improvements in the signaling systems, track
design and layout, coach interiors for better riding comfort and capacity, etc., along with
improvements in locomotives. Improvements are being planned by engineers. The workshops of
the railways too have been given new equipment to create sophisticated coaches at Perambur and
Kapurthala and diesel engine parts at Patiala. Locomotives are being made at Chittaranjan and
Varanasi. This is in sharp contrast to the earlier British conviction that only minor repairs would

15. be possible in India, so all spare parts including nuts and bolts for locomotives would have to be
imported from England. More trains and routes are constantly being added to the railway
network and services. The British legacy lives on in our railway system, transformed but never
forgotten. Long live the Romance of the Rails! The network of lines has grown to about 62,000
kilometers. But, the variety of Indian Railways is infinite. It still has the romantic toy trains on
narrow gauge hill sections, meter gauge beauties on other and broad gauge bonanzas as one visits
places of tourist interest courtesy Indian Railways! They are an acknowledgement of the
Railways that tourism as an industry has to be promoted and that India is full of unsurpassed
beauty. The Calcutta Metro is a fine example of highly complex engineering techniques being
adopted to lay an underground railway in the densely built-up areas of Calcutta city. It is a treat
to be seen. The Calcuttans keep it so clean and tidy that not a paper is thrown around! It only
proves the belief that a man grows worthy of his superior possessions. Calcutta is also the only
city where the Metro Railway started operating from September 27, 1995 over a length of 16.45
km. There is also a Circular Railway from Dum Dum to Princep Ghats covering 13.50 km to
provide commuter trains.
In time of war and natural disasters, the railways play a major role. Whether it was the
earthquake of 1935 in Quetta (now in Pakistan) or more recently in Latur in Maharashtra, it is the
railways that muster their strength to carry the sick and wounded to hospitals in nearby towns
and to the people of the affected areas. In rehabilitation and reconstruction, too, their role is vital.
During the Japanese war, the Indian Railways added further laurels to their record as they
extended the railway line right up to Ledo in the extreme northeastern part of Assam and thus
enabled the Allied forces under General Stillwell to combat the Japanese menace. In fact, several
townships in Assam like Margherita and Digboi owe their origin to the endeavors of the Indian
Railways. It was the Assam Railway and Trading Company that opened up the isolated regions
of Assam with the laying of the railway lines and thus providing the lifeline to carry coal, tea,
and timber out of the area and bring other necessary commodities to Assam and the adjoining
countryside. Now, the Indian Railways system is divided into 9 zonal railways, a metro railway,
Calcutta, the production units, construction organizations, and other railway establishments.

16. 2. OPTICALFIBRE COMMUNICATION SYSTEM
2.1 OPTICAL FIBRE
An optical fiber is a cylindrical dielectric waveguide
made of low-loss materials such as silica glass. It has a
central core in which the light is guided, embedded in
an outer cladding of slightly lower refractive index.
Light rays incident on the core-cladding boundary at
angles greater than the critical angle undergo total
internal reflection and are guided through the core
without refraction. Rays of greater
inclination to the fiber axis lose part of their power
into the cladding at each reflection and are not guided.
As a result of recent technological advances in
fabrication, light can be guided through 1 km of glass
fiber with a loss as low as = 0.16 dB (= 3.6 %). Optical
fibers are replacing copper coaxial cables as the
preferred transmission medium for electromagnetic
waves, thereby revolutionizing terrestrial
communications. Applications range from long-
distance telephone and data communications to
computer communications in a local area network.

17. 2.1.1 Single-mode and multimode opticalfibres
 Multimode is 50/125 or 62.5/125 

 50 micron is the CORE 

 125 micron is the Cladding 
 Single mode is 8‐10/125 
 8‐10 micron is the CORE 

 125 micron is the Cladding 
2.1.2 Operational Parameters
 1 st Window – 850 nm allows cheap LED‘s to operate over reasonable distances (km) 

 2 nd Window – 1300nm more expensive LED‘s and Lasers operate over longer distances
(10‘s of Km). Fiber attenuation at this level is less than at 850nm 

 3 rd Window – 1550nm employs expensive sophisticated laser /detected systems. Long
distance without repeaters (100‘s of Km) 

18. Multimode optical fibers are dielectric waveguides which can have many propagation modes.
Light in these modes follows paths that can be represented by rays as shown in Figure 1-1a and 1-1b,
where regions 1, 2 and 3 are the core, cladding and coating, respectively. The cladding glass has a
refractive index, a parameter related to the dielectric constant, which is slightly lower tha n the refractive
index of the core glass.
Figure 1-1 – The three principal types of fibres
The fiber in Figure 1-1a is called ―step index‖ because the refractive index changes
abruptly from cladding to core. As a result, all rays within a certain angle will be totally reflected
at the core-cladding boundary. Rays striking the boundary at angles greater than this critical

19. angle will be partially reflected and partially transmitted out through the boundary towards the
cladding and coating. After many such reflections, the energy in these rays will eventually be
lost from the fibre. Region 3, the coating, is a plastic which protects the glass from abrasion.
The paths along which the rays (modes) of this step-index fibre travel differ depending on
their angle relative to the axis. As a result, the different modes in a pulse arrive at the far end of
the fibre at different times, resulting in pulse spreading, which limits the bit rate of a digital
signal that can be transmitted.
The different mode velocities can be nearly equalized by using a ―graded-index‖ fibre as
shown in Figure 1-1b. Here the refractive index changes smoothly from the centre out in a way
that causes the end-to-end travel time of the different rays to be nearly equal, even though they
traverse different paths. This velocity equalization can reduce pulse spreading by a factor of 100
or more. By reducing the core diameter and the refractive index difference between the core and
the cladding only one mode (the fundamental one) will propagate and the fibre is then ―single-
mode‖ (Figure 1-1c). In this case there is no pulse spreading at all due to the different
propagation time of the various modes.
The cladding diameter is 125 μm for all the telecommunication types of fibres. The core
diameter of the multimode fibres is 50 μm, whereas that of the single-mode fibres is 8 to 10 μm.
2.1.3 The Designof Fiber Core and Cladding
An optical fiber consists of two different types of highly pure, solid glass, composed to
form the core and cladding. A protective acrylate coating (see Figure 1) then surrounds the
cladding. In most cases, the protective coating is a dual layer composition.

20. A protective coating is applied to the glass fiber as the final step in the manufacturing
process. This coating protects the glass from dust and scratches that can affect fiber strength.
This protective coating can be comprised of two layers: a soft inner layer that cushions the fiber
and allows the coating to be stripped from the glass mechanically and a harder outer layer that
protects the fiber during handling, particularly the cabling, installation, and termination
processes.
2.1.4 Single-Mode andMultimode Fibers
Multimode fiber was the first type of fiber to be commercialized. It has a much larger
core than single-mode fiber, allowing hundreds of modes of light to propagate through the fiber
simultaneously. Additionally, the larger core diameter of multimode fiber facilitates the use of
lower-cost optical transmitters (such as light emitting diodes [LEDs] or vertical cavity surface
emitting lasers [VCSELs]) and connectors.
Single-mode fiber, on the other hand, has a much smaller core that allows only one mode
of light at a time to propagate through the core. While it might appear that multimode fibers have
higher capacity, in fact the opposite is true. Singlemode fibers are designed to maintain spatial
and spectral integrity of each optical signal over longer distances, allowing more information to
be transmitted. Its tremendous information-carrying capacity and low intrinsic loss have made
single-mode fiber the ideal transmission medium for a multitude of applications. Single-mode
fiber is typically used for longer-distance and higher-bandwidth applications (see Figure 3).
Multimode fiber is used primarily in systems with short transmission distances (under 2 km),
such as premises communications, private data networks, and parallel optic applications.

21. 2.1.5 OpticalFiber Sizes
The international standard for
outer cladding diameter of most single-
mode optical fibers is 125 microns (μm)
for the glass and 245 μm for the coating.
This standard is important because it
ensures compatibility among connectors,
splices, and tools used throughout the
industry.
Standard single-mode fibers are
manufactured with a small core size,
approximately 8 to 10 μm in diameter.
Multimode fibers have core sizes of 50 to
62.5 μm in diameter.
2.2 Fiber Geometry Parameters
The three fiber geometry parameters
that have the greatest impact on
splicing performance include the
following:
 core/clad concentricity (or core-to-cladding offset): how well the core is
centered in the cladding glass region. 

 fiber curl: the amount of curvature over a fixed length of fiber These
parameters are determined and controlled during the fiber-manufacturing
process. As fiber is cut and spliced according to system needs, it is important to 

22. be able to count on consistent geometry along the entire length of the fiber and
between fibers and not to rely solely on measurements made.
2.2.1 Cladding Diameter
The cladding diameter tolerance controls the outer diameter of the fiber, with tighter
tolerances ensuring that fibers are almost exactly the same size. During splicing, inconsistent
cladding diameters can cause cores to misalign where the fibers join, leading to higher splice
losses. The drawing process controls cladding diameter tolerance, and depending on the
manufacturer‘s skill level, can be very tightly controlled.
2.2.2 Core/CladConcentricity
Tighter core/clad concentricity tolerances help ensure that the fiber core is centered in
relation to the cladding. This reduces the chance of ending up with cores that do not match up
precisely when two fibers are spliced together. A core that is precisely centered in the fiber
yields lower-loss splices more often.
Core/clad concentricity is determined during the first stages of the manufacturing
process, when the fiber design and resulting characteristics are created. During these laydown
and consolidation processes, the dopant chemicals that make up the fiber must be deposited with
precise control and symmetry to maintain consistent core/clad concentricity performance
throughout the entire length of fiber.
2.2.3 FiberCurl
Fiber curl is the inherent curvature along a specific length of optical fiber that is exhibited
to some degree by all fibers. It is a result of thermal stresses that occur during the manufacturing
process. Therefore, these factors must be rigorously monitored and controlled during fiber
manufacture. Tighter fiber-curl tolerances reduce the possibility that fiber cores will be
misaligned during splicing, thereby impacting splice loss. Some mass fusion splicers use fixed v-
grooves for fiber alignment, where the effect of fiber curl is most noticeable.

23. 2.2.4Dispersion
Dispersion is the time distortion of an optical signal that results from the time o flight
differences of different components of that signal, typically resulting in pulse broadening (see
Figure 10). In digital transmission, dispersion limits the maximum data rate, the maximum
distance, or the information-carrying capacity of a single-mode fiber link. In analog
transmission, dispersion can cause a waveform to become significantly distorted and can result in
unacceptable levels of composite second-order distortion (CSO).
2.3 OPTICAL FIBRE COMMUNICATION
2.3.1 Historicalperspective of opticalcommunication
The use of light for transmitting information from one place to another place is a very old
technique. In 800 BC., the Greeks used fire and smoke signals for sending information like
victory in a war, alertting against enemy, call for help, etc. Mostly only one type of signal was
conveyed. During the second century B.C. optical signals were encoded using signaling lamps so
that any message could be sent. There was no development in optical communication till the end
of the 18th century. The speed of the optical communication link was limited due to the
requirement of line of sight transmission paths, the human eye as the receiver and unreliable

24. nature of transmission paths affected by atmospheric effects such as fog and rain. In 1791,
Chappe from France developed the semaphore for telecommunication on land. But that was also
with limited information transfer.
In 1835, Samuel Morse invented the telegraph and the era of electrical communications
started throughout the world. The use of wire cables for the transmission of Morse coded signals
was implemented in 1844. In 1872, Alexander Graham Bell proposed the photo phone with a
diaphragm giving speech transmission over a distance of 200 m. But within four years, Graham
Bell had changed the photophone into telephone using electrical current for transmission of
speech signals. In 1878, the first telephone exchange was installed at New Haven. Meanwhile,
Hertz discovered radio waves in 1887. Marconi demonstrated radio communication without
using wires in 1895. Using modulation techniques, the signals were transmitted over a long
distance using radio waves and microwaves as the carrier.
During the middle of the twentieth century, it was realized that an increase of several
orders of magnitude of bit rate distance product would be possible if optical waves were used as
the carrier.
In the old optical communication system, the bit rate distance product is only about 1
(bit/s)-km due to enormous transmission loss (105 to 107 dB/km). The information carrying
capacity of telegraphy is about hundred times lesser than a telephony. Even though the high-
speed coaxial systems were evaluated during 1975, they had smaller repeater spacing.
Microwaves are used in modern communication systems with the increased bit rate distance
product. However, a coherent optical carrier like laser will have more information carrying
capacity. So the communication engineers were interested in optical communication using lasers
in an effective manner from 1960 onwards. A new era in optical communication started after the
invention of laser in 1960 by Maiman. The light waves from the laser, a coherent source of light
waves having high intensity, high monochromaticity and high directionality with less
divergence, are used as carrier waves capable of carrying large amount of information compared
with radio waves and microwaves. Subsequently H M Patel, an Indian electrical engineer
designed and fabricated a CO2 laser.

25. 2.3.2 The birth of fiber optic systems
To guide light in a waveguide, initially metallic and non-metallic wave guides were
fabricated. But they have enormous losses. So they were not suitable for telecommunication.
Tyndall discovered that through optical fibers, light could be transmitted by the phenomenon of
total internal reflection. During 1950s, the optical fibers with large diameters of about 1 or 2
millimeter were used in endoscopes to see the inner parts of the human body.
Optical fibers can provide a much more reliable and versatile optical channel than the
atmosphere, Kao and Hockham published a paper about the optical fiber communication system
in 1966. But the fibers produced an enormous loss of 1000 dB/km. But in the atmosphere, there
is a loss of few dB/km. Immediately Kao and his fellow workers realized that these high losses
were a result of impurities in the fiber material. Using a pure silica fiber these losses were
reduced to 20 dB/km in 1970 by Kapron, Keck and Maurer. At this attenuation loss, repeater
spacing for optical fiber links become comparable to those of copper cable systems. Thus the
optical fiber communication system became an engineering reality.
2.3.3 Basic opticalfiber communication system
Figure 2 shows the basic components in the optical fiber communication system. The input
electrical signal modulates the intensity of light fromthe optical source. The optical carrier can be
modulated internally or externally using an electro-optic modulator (or) acousto-optic modulator.
Nowadays electro-optic modulators (KDP, LiNbO3 or beta barium borate) are widely used as
external modulators which modulate the light by changing its refractive index through the given
input electrical signal. In the digital optical fiber communication system, the input electrical
signal is in the form of coded digital pulses from the encoder and these electric pulses modulate
the intensity of the light from the laser diode or LED and convert them into optical pulses. In the
receiver stage, the photo detector like avalanche photodiode (APD) or positive-intrinsic negative
(PIN) diode converts the optical pulses into electrical pulses. A decoder converts the electrical
pulses into the original electric signal.

26. Figure Basic analog optical fiber communication system.
Table Different generations of optical fiber communication systems
Table 2 shows the different generations of optical fiber communication. In generation I, mostly
GaAs based LEDs and laser diodes having emission wavelength 0.8 micrometer were used from
1974 to 1978, graded index multimode fibers were used. From 1978 onwards, only single mode
fibers are used for long distance communication. During the second generation the operating
wavelength is shifted to 1.3 micrometer to overcome loss and dispersion. Further InGaAsP
hetero-junction laser diodes are used as optical sources. In the third generation the operating
wavelength is further shifted to 1.55 micrometer m and the dispersion-shifted fibers are used.
Further single mode direct detection is adopted. In the fourth generation erbium doped optical

27. (fiber) amplifiers are fabricated and the whole transmission and reception are performed only in
the optical domain. Wavelength Division Multiplexing (WDM) is introduced to increase the bit
rate. In the proposed next generation (V generation), soliton based lossless and dispersion less
optical fiber communication will become a reality. At that time, the data rate may increase
beyond 1000 Tb/s.
2.3.4 Advantages ofoptical fiber communication
1. Wider bandwidth: The information carrying capacity of a transmission system is directly
proportional to the carrier frequency of the transmitted signals. The optical carrier frequency is in
the range 1013 to 1015 Hz while the radio wave frequency is about 106 Hz and the microwave
frequency is about 1010 Hz. Thus the optical fiber yields greater transmission bandwidth than
the conventional communication systems and the data rate or number of bits per second is
increased to a greater extent in the optical fiber communication system. Further the wavelength
division multiplexing operation by the data rate or information carrying capacity of optical fibers
is enhanced to many orders of magnitude.
2. Low transmission loss: Due to the usage of the ultra-low loss fibers and the erbium doped
silica fibers as optical amplifiers, one can achieve almost lossless transmission. In the modern
optical fiber telecommunication systems, the fibers having a transmission loss of 0.002 dB/km
are used. Further, using erbium doped silica fibers over a short length in the transmission path at
selective points, appropriate optical amplification can be achieved. Thus the repeater spacing is
more than 100 km. Since the amplification is done in the optical domain itself, the distortion
produced during the strengthening of the signal is almost negligible.
3. Dielectric waveguide: Optical fibers are made from silica which is an electrical insulator.
Therefore they do not pickup any electromagnetic wave or any high current lightning. It is also
suitable in explosive environments. Further the optical fibers are not affected by any interference
originating from power cables, railway power lines and radio waves. There is no cross talk
between the fibers even though there are so many fibers in a cable because of the absence of
optical interference between the fibers.
4. Signal security: The transmitted signal through the fibers does not radiate. Further the signal
cannot be tapped from a fiber in an easy manner. Therefore optical fiber communication
provides hundred per cent signal security.

28. 5. Small size and weight: Fiber optic cables are developed with small radii, and they are flexible,
compact and lightweight. The fiber cables can be bent or twisted without damage. Further, the
optical fiber cables are superior to the copper cables in terms of storage, handling, installation
and transportation, maintaining comparable strength and durability.
2.4 PULSE CODE MODULATION
Pulse code modulation (PCM) is the process of converting an analog signal into a 2n-
digit binary code. Consider the block diagram shown in Figure 8-9. An analog signal is placed on
the input of a sample and hold. The sample and hold circuit is used to ―capture‖ the analog
voltage long enough for the conversion to take place. The output of the sample and hold circuit is
fed into the analog-to-digital converter (A/D). An A/D converter operates by taking periodic
discrete samples of an analog signal at a specific point in time and converting it to a 2n-bit binary
number. For example, an 8-bit A/D converts an analog voltage into a binary number with 28
discrete levels (between 0 and 255). For an analog voltage to be successfully converted, it must
be sampled at a rate at least twice its maximum frequency. This is known as the Nyquist
sampling rate. An example of this is the process that takes place in the telephone system.
Standard telephone has a bandwidth of 4 kHz. When you speak into the telephone, your 4-kHz
bandwidth voice signal is sampled at twice the 4-kHz frequency or 8 kHz. Each sample is then
converted to an 8-bit binary number. This occurs 8000 times per second. Thus, if we multiply
8 k samples/s × 8 bits/sample = 64 kbits/s
Temporarily store the digital codes during the conversion process. The DAC accepts an n-bit
digital number and outputs a continuous series of discrete voltage ―steps.‖ All that is needed to
smooth the stair-step voltage out is a simple low-pass filter with its cutoff frequency set at the
maximum signal frequency.

29. Figure PCM (a) Block diagram (b) Digital waveforms

30. Figure D/A output circuit
2.5 MULTIPLEXING
The purpose of multiplexing is to share the bandwidth of a single transmission channel among
several users. Two multiplexing methods are commonly used in fiber optics:
1. Time-division multiplexing (TDM)
2. Wavelength-division multiplexing (WDM)
2.5.1 Time-DivisionMultiplexing (TDM)
In time-division multiplexing, time on the information channel, or fiber, is shared among the
many data sources. The multiplexer MUX can be described as a type of ―rotary switch,‖ which
rotates at a very high speed, individually connecting each input to the communication channel
for a fixed period of time. The process is reversed on the output with a device known as a
demultiplexer, or DEMUX. After each channel has been sequentially connected, the process
repeats itself. One complete cycle is known as a frame. To ensure that each channel on the input
is connected to its corresponding channel on the output, start and stop frames are added to
synchronize the input with the output. TDM systems may send information using any of the
digital modulation schemes described (analog multiplexing systems also exist). This is illustrated
in Figure 8-15.
Figure

31. 2.6 FIBER OPTIC SOURCES
Two basic light sources are used for fiber optics: laser diodes (LD) and light-emitting
diodes (LED). Each device has its own advantages and disadvantages as listed in Table.
Fiber optic sources must operate in the low-loss transmission windows of glass fiber.
LEDs are typically used at the 850-nm and 1310-nm transmission wavelengths, whereas lasers
are primarily used at 1310 nm and 1550 nm.
LEDs are typically used in lower-data-rate, shorter-distance multimode systems because of their
inherent bandwidth limitations and lower output power. They are used in applications in which
data rates are in the hundreds of megahertz as opposed to GHz data rates associated with lasers.
Two basic structures for LEDs are used in fiber optic systems: surface-emitting and edge
emitting

32. In surface-emitting LEDs the radiation emanates from the surface. An example of this is
the Burris diode as shown in Figure 8-21. LEDs typically have large numerical apertures, which
makes light coupling into single-mode fiber difficult due to the fiber‘s small N.A. and core
diameter. For this reason LEDs are most often used with multimode fiber. LEDs are used in
lower-data-rate, shorter-distance multimode systems because of their inherent bandwidth
limitations and lower output power. The output spectrum of a typical LED is about 40 nm, which
limits its performance because of severe chromatic dispersion. LEDs operate in a more linear
fashion than do laser diodes. This makes them more suitable for analog modulation. Figure 8-22
shows a graph of typical output power versus drive current for LEDs and laser diodes. Notice
that the LED has a more linear output power, which makes it more suitable for analog
modulation. Often these devices are pigtailed, having a fiber attached during the manufacturing
process. Some LEDs are available with connector-ready housings that allow a connectorized
fiber to be directly attached. They are also relatively inexpensive. Typical applications are local
area networks, closed-circuit TV, and transmitting information in areas where EMI may be a
problem.
Laser diodes (LD) are used in
applications in which longer distances
and higher data rates are required.
Because an LD has a much higher

33. output power than an LED, it is capable
of transmitting information over longer
distances. Consequently, and given the
fact that the LD has a much narrower
spectral width, it can provide high-bandwidth communication over long distances. The LD‘s
smaller N.A. also allows it to be more effectively coupled with single-mode fiber. The difficulty
with LDs is that they are inherently nonlinear, which makes analog transmission more difficult.
They are also very sensitive to fluctuations in temperature and drive current, which causes their
output wavelength to drift. In applications such as wavelength division multiplexing in which
several wavelengths are being transmitted down the same fiber, the stability of the source
becomes critical. This usually requires complex circuitry and feedback mechanisms to detect and
correct for drifts in wavelength. The benefits, however, of high-speed transmission using LDs
typically outweigh the drawbacks and added expense.
Laser diodes can be divided into two generic types depending on the method of confinement of
the lasing mode in the lateral direction.
 Gain-guided laser diodes work by controlling the width of the drive-current distribution;
this limits the area in which lasing action can occur. Because of different confinement
mechanisms in the lateral and vertical directions, the emitted wavefront from these
devices has a different curvature in the two perpendicular directions. This astigmatism in
the output beam is one of the unique properties of laser-diode sources. Gain-guided
injection laser diodes usually emit multiple longitudinal modes and sometimes multiple
transverse modes. The optical spectrum of these devices ranges up to about 2 nm in
width, thereby limiting their coherence length. 

 Index-guided laser diodes use refractive index steps to confine the lasing mode in both
the transverse and vertical directions. Index guiding also generally leads to both single
transverse mode and single longitudinal-mode behavior. Typical linewidths are on the
order of 0.01 nm. Index-guided lasers tend to have less difference between the two 
perpendicular divergence angles than do gain-guided lasers.
Single-frequency laser diodes are another
interesting member of the laser diode family. These
devices are now available to meet the requirements for

34. high-bandwidth communication. Other advantages of
these structures are lower threshold currents and lower
power requirements. One variety of this type of
structure is the distributed-feedback (DFB) laser diode
(Figure). With introduction of a corrugated structure into the cavity of the laser, only light of a
very specific wavelength is diffracted and allowed to oscillate. This yields output wavelengths
that are extremely narrow—a characteristic required for DWDM systems in which many closely
spaced wavelengths are transmitted through the same fiber. Distributed-feedback lasers have
been developed to emit light at fiber optic communication wavelengths between 1300 nm and
1550 nm.
2.7 FIBER OPTIC DETECTORS
The purpose of a fiber optic detector is to convert light emanating from the optical fiber
back into an electrical signal. The choice of a fiber optic detector depends on several factors
including wavelength, responsively, and speed or rise time. Figure 8-30 depicts the various types
of detectors and their spectral responses.
The process by which light is converted into an electrical signal is the opposite of the
process that produces the light. Light striking the detector generates a small electrical current that
is amplified by an external circuit. Absorbed photons excite electrons from the valence band to
the conduction band, resulting in the creation of an electron-hole pair. Under the influence of a
bias voltage these carriers move through the material and induce a current in the external circuit.
For each electron-hole pair created, the result is an electron flowing in the circuit. Typical
current levels are small and require some amplification as shown in Figure 8-31.

35. The most commonly used photo detectors are the PIN and avalanche photodiodes (APD).
The material composition of the device determines the wavelength sensitivity. In general, silicon
devices are used for detection in the visible portion of the spectrum; InGaAs crystal are used in
the near-infrared portion of the spectrum between 1000 nm and 1700 nm, and germanium PIN
and APDs are used between 800 nm and 1500 nm.
2.8 OPTICAL NETWORK CONFIGURATION
 More complex network than long-haul point-
to-point. 

 Reconfigurable add/drop multiplexers
(ROADM) are the current technology that
enable the network bandwidth to be
dynamically switched based on need. 

 Up to 80 wavelengths separated by 100 GHz =
0.8 nm at 1550 nm, each carrying 10 Gb/s for
a total of 800 Gb/sec. 


36.  This system has been replaced with models
offering well in excess of 1 Tb/s. 
2.9 Network architecture
 Many-layered network from internet browser on your laptop wirelessly connected to a
coffee-shop (application layer = top) to bursts of light on fiber (physical layer = bottom). 

 At the lowest, physical layer, the network is mainly static, point-to-point links. 

 Circuit switching of the physical optical network is starting 

 Packet switching at the physical optical layer is a research topic 






37. 





Railnet – An Overview
3.1 Introduction:
Railnet is the name of the Corporate Wide Information System (CWIS) of Indian Railways. It is
aimed to provide computer connectivity between Railway Board, Zonal Railways, Production units,
RDSO, Centralized Training Institutes, CORE, MTP/Kolkata etc.
3.2 Objectives:
Railnet has been established with these objectives in mind:
●Eliminate the need to move paper documents between different documents and
●Change from “Periodic Reporting” to “Information on Demand.”
Railnet will expedite and facilitate quick and efficient automatic status update between Railway
Board and Zonal Railway, as well as between divisions and Zonal Railway. Internet gateways have
been established at Delhi, Mumbai, Chennai, Kolkatta and Secunderabad for access of Internet
through Railnet.
3.3 Railnet General Arrangement:

38. Fig. 3.3(a)



The general arrangement of the equipment’s used in Railnet is shown in the diagram above. The
WAN link (or the Railnet link) terminates at the router. The router in turn is connected to the switch.
All the computers including the server is connected to the switch. Additional hubs/switches may be
connected to this switch so as to extend the Railnet LAN further.
Railnet users can exchange emails on the Internet. Commercial Dept. is extensively using Railnet
for their “Complaint Center.” Railways have launched their web pages and they keep up to date
information in these web pages. A Railnet authorized user can browse the Internet through Railnet.
A Railnet user can share resources with a co-user on Railnet.
3.4 The Railnet Work:
The Railnet Work was proposed to be completed in three phases. Phase I is planned to connect
all the zonal Railway and production units with Railway Board. Phase II consists of connecting
the divisions to the zonal Railways as well as connection the following to the Railway board.
●RDSO/LKO
●CORE/ALD
●MTP/CAL
●CTIs viz. IRISET, IREEN, IRICEN, RSC, IRMEE
●Major Training centers
Phase III will connect the divisions with the important places like important stations, stores depot
etc.
Phase I of Railnet was commissioned by IRCOT1 through a contract agreement with Tata
Infotech. IRCOT had done the following:
1 .Procurement, Installation and commissioning of Server, Router, switches, modems etc.
2. Testing and commissioning of Data Links.
3. Loading and configuration of system software.
4. Training of Railway personnel.

39. The maintenance of Railnet infrastructure and the web pages is done by the concerned Railways.
IRCOT has arranged proper training for officers as well as supervisors so that the maintenance
becomes easy.

Railnet Phase I (Connectivity Diagram).
Fig. 3.4(a)
The connectivity diagram of Railnet Phase I is shown above. This constitute the backbone of
Railnet. This phase connects the zonal headquarters of WR, ER, SR, NR to the Railway Board. The
zonal HQ of SER, NFR, NER, CR and SCR are connected to one of the zonal HQ so as to get
connectivity with Railway Board. The production units are also connected to the zones nearest to
then so as to get connected with railway Board.



40. 





Railnet Phase II (Connectivity Diagram).
Fig. 3.4(b)
The Railnet Phase II connectivity diagram is shown below. The backbone was further extended in
this phase by a direct connection between SCR Hqs and Railway Board. The zonal Railways were
connected to their divisions in this phase. The CTIs were connected to zones nearest to them in this
phase. The major training centres were also connected to Railnet in this phase. With the completion
of Railnet Phase II, the major portion of Railnet is in place and working. The Phase III that aims at
extending it further to stores depot etc. is being done at present.



41. 





Railnet Phase IIl (Connectivity Diagram).
Fig. 3.4(c)
The diagram above shows the planned Railnet connectivity after Phase III. Almost all of Indian
Railways will be connected to Railnet after this phase.
3.5 Network Topology:
The network in which the terminals are interconnected with each other for inter communication within

42. and outside the network is called as Topology.
Basically the Topology is categorized in following four types of designs.



(a) Mesh topology-
In mesh topology every device has a dedicated point to point to every
other device. Every device must have (n-1) I/O ports. All WAN is mesh topology.
Fig. 3.5a Fully connected mesh topology (for five devices)
Advantages are:
 It is robust. 
 Each link can carry its own data load. 
 It has privacy or secrecy. 
 Fault identification is easy 

43. 
Mesh disadvantages are larger number of cables & I/O ports are required for each device.
Also the bulk of the wires can be greater than the available space.
(b) Star topology-
In star topology each device has a dedicated point to point link only to central
controller called as HUB as shown. If one device wants to send data to another device, it sends
through the HUB.
Fig. 3.5b Star topology
Advantages are
 It is easy to install and reconfigure. 
 Each device needs only one link. Hence it is less expensive. 
 If a link fails, only that link has to be attended. All other links remain active. 
 It is easy to identify fault. 
 It is also robust. 
(c) Bus topology-
A BUS topology is multipoint. One long cable acts as a backbone to link all devices
in a network. The advantage is the installation is easy.

44. Fig. 3.5c Bus topology
Disadvantages are
 Difficult in fault isolation and reconnection. 
 Difficult to add device to an exsisting system. 
 A fault or break in bus cable stops all transmission. 


(d)Ring topology-
In a ring topology, each has a dedicated point to point connection only with two
devices on either side of it. A data is passed along the ring in one direction, from device to device
until it reaches its destination. Each device in a ring incorporates a repeater.
Fig. 3.5d Ring topology
The advantages are
 It is easy to install & configure. 
 The disadvantages are unidirectional traffic and a break in the ring can disable entire
network. 
 To add or delete a device requires only changing two connections. 

45. 3.6 Categories of Networks:
Networks are categorized in three different categories as
 LAN (Local Area Network) 
 MAN (Metropolitan Area Network) 
 WAN (Wide Area Network) 
Fig. 3.6a Classification of Networks
(a) LAN (Local Area Network)-
Local Area Networks (LANs) are networks that connect computers
and resources together in a building or buildings close together. The computers share resources
such as hard-drives, printers, data, CPU power, fax/modem, applications, etc... They usually have
distributed processing - means that there is many desktop computers distributed around the
network and that there is no central processor machine (mainframe).
Fig. 3.6a Local Area Network
Location: In a building or individual rooms or floors of buildings or connecting nearby buildings
together like a campus wide network like a college or university.

46. b MAN (Metropolitan Area Network)-
Metropolitan Area Networks (MANs) are networks that
connect LANs together within a city. From The Big Picture, we see that telecommunication services
provide the connection (storm clouds) between networks. A local telecommunication service
provides the external connection for joining networks across cities.
Fig. 3.6b Metro Area networks
Location: Separate buildings distributed throughout a city. Examples of companies that use
MANs are universities, colleges, grocery chains, gas stations, department stores and banks.
c WAN (Wide Area Network)-
Wide Area Networks (WAN) are a communication system linking
LANs between cities, countries and continents. The main difference between a MAN and a WAN is
that the WAN uses Long Distance Carriers rather than Local Exchange carriers. Otherwise the same
protocols and equipment are used as a MAN.
Fig. 3.6c Wide area network
Location: City to city, across a country or across a continent. Wide Area Networks (WANs) connect
LANs together between cities or across a country.

47. PRS & UTS Network
4.Introduction:-
With the implementation of computerized passenger reservation system on Northern Railway in
year 1985-86 at New Delhi, a modest beginning was made which has completely revolutionized the
process of passenger reservation service on Indian Railways. To begin with the computerized
reservation at Delhi was implemented on small VAX-750 computer with just 30 terminals. Today it is
a matter of great pride and satisfaction that highly complex but successful network of computerized
reservation is available at more than 20 major towns including 4 metros of India, covering almost
25% of the reservation facility available on IR. PRS is equipped with latest state of art technology
both in the field of computer and data communication systems.
As a matter of policy and due to technical reasons, it was decided to have PRS computers only at
Delhi, Bombay, Madras, Calcutta and Secunderabad which cover bulk of reservation volume and to
have remote terminals at other major cities connected to host PRS computers through data links.
Today all PRS hosts are CRIS to network all the computers to provide an integrated reservation
system on IR.
Unreservation Ticketing System (UTS) is like as PRS but it have an external devise which store
ticketing information and upload on server.
4.1Interconnection of PRS & UTS Servers:
4.2PREVIOUS SET UP AT PRS/DELHI:

48. 4.3CONCERT APPLICATION ARCHITECTURE:
Fig. 2.3a

49. Other aspects of PRS:
Use of satellite data links- The Remote Area Business Messaging Network (RABMN) of Dot
commissioned recently may be tried for linking remote stations where normal BSNL links may not
be available or are unreliable. (E.g. North frontier areas from Calcutta PRS) Direct terminals or
teleprinter interfaces might be used sharing one VSAT link working at 1200 bps, provided the rental
and other maintenance costs do not become prohibitive.
Use of Radio Frequency modems- Trials have been conducted using Radio frequency
modems interfaced to VHF half duplex sets and connecting PRS terminals through this data link.
1200 and 2400 bps speeds have been found to be quite successful on WEBEL make VHF sets.
Extension of 1 or 2 terminals at a radius of 8 to 10 Kms with a reasonable line of sight will be
possible at a cheap cost through these modems.
4.4Benefits of PRS:
(a) To the Passengers-
Transparency
Universal counters for booking
Instant update of status
Instantaneous enquiry
Reduced waiting time
Reservation available at a number of locations in the country
Customer satisfaction
(b) To the Railways-
Increased efficiency
Optimal utilization of berths
Real time availability of Accounting Reports
Planning through MIS reports
Analysis of traffic pattern for better overall planning
Reduction in Revenue losses
Saving on Manpower
Eliminate possibilities of fraud

50. 4.5Technology used:
Hardware
DS20 Alpha machines under Tru 64 Unix 4.0 f
4.6 Software
C,RTR 3.2
Sybase with Replication
4.7Future Enhancements:
Improvements in the response time in the Dynamic (PNR and Seat availability) enquiries.
Other transport information (Road/Air/Water) for major tourist locations
Dynamic Enquiries in Hindi
Providing dynamic enquiries for 24 hours.
4.8New challenges:
Maintenance by remote login by vpn
By HP engineers in US or Bangalore
Regular proactive patch updation

51. Exchange
4.1 Introduction:
C-DOT 128P RAX is a Telephone exchange designed to meet the telecommunication
needs of small sized rural areas. These exchanges are also suitable for Indian Railway applications
where the telephone line capacity is less than 100. Provision is made in the design to expand the
line capacity up to 400 subscribers roughly.
C-DOT (Centre for Development of Telematics) is a Central government organization of India set up
to develop the necessary equipment’s (infrastructure) suitable for Indian climate and environmental
conditions. The system is designed to offer uninterrupted services by using duplicating methods for
control and power supply circuits. Tone generator circuit is also duplicated.
4.2 Power Supply Unit card:
The input voltage is –48+/-4V. The RAX system requires various internal working voltage sources.
PSU card provides the following output voltages for internal working.
1) +5V-8A – For microprocessor and other digital components.
2) –9V-0.5A – Codec
3) +12V-1A – Relays
4) –5V-0.1A – For other digital components.
5) –48V – For speech

52. 4.3 RAX Control processor (RCP):
This card uses 65C02 Micro Processor and has 12K RAM, 48K EPROM & 16K EEPROM
memories. This contains the information pertaining to peripheral cards, metering and other
administrative functions to be performed. Maintenance panel is connected directly to RCP by which
any changes in the data of the exchange can be made (adding, deleting, modifying of subscriber or
trunks etc.).
The main functions RCP are Call processing, Administration and Maintenance . The functional
block diagram is shown in fig 4.3a.
Fig. 4.3a Functional Block diagram of RCP card
1. FUNCTIONAL BLOCKS -
a. Processor and Memory.
b. Clock Generation.
c. Address Decoder and Read/Write Generator.
d. Asynchronous Communication and Timer.
e. Error Monitor.
f. EEPROM and Real Time Clock.
g. High Level Data Link Control.

53. 4.4 Switching Network (TIC):
The TIC/SN is essentially a generic card. It switches voice between the 128 ports, controls
signalling, support diagnostics and duplication under the intelligence of RCP. It can be understood
this way also. The signalling of the termination cards is handled by the signal processor (SP) and
voice by the Switching Network (SN). Both SP and SN are under the control of Terminal Interface
Controller (TIC) which works under instruction from RCP.
1. FUNCTIONS-
1) TIC/SN Switches the PCM (Pulse Code Modulation) digital voice information. This is
to enable the subscribers to converse with each other and to be fed with different tones
at different stages of the call.
2) TIC (Terminal Interface Controller) derives the identities of the calling and called
terminals and establishes a path through SN (Switching Network) between these
terminals. TIC communicates with RCP on HDLC (High Level Data Link Control)
for call related information.
3) Using SPC (Signal Processor Card) it receives status indication for all the 128 port
(terminals) i.e. scan signalling information. This information is passed on to RCP. Also it
gets the message from RCP to drive events on terminals and passes the Drive signalling
information to signal processor. Note: (HDLC) is to ensure that data is transferred
quickly and correctly.
4) It keeps on doing periodic diagnostic on the terminal cards including itself and
informing RCP through HDLC messages.

54. 4.5 Tone generator with Diagnostic card (TGS):
Tone Generator card is used to generate call supervisory and test tones for system like
PABX and RAX. It has also capability to diagnosis the tones it produces and thereby can conform
sanity check of the voice path.
Figure 4.5a TG
(a) A tone is a simple audio signal having distinct frequency or set of frequencies (usually a voice
frequency i.e. between 20 Hz to 20 KHz).
(b) A tone may be continuous or may have cadence i.e. signal has certain ON – OFF period.
(c) A tone consists of one or more tone components.

55. (d) A tone component may mean a single frequency signal (400 Hz) or a modulated frequency
signal (400 Hz modulated by 25 Hz) or it can be an addition of two sine waves of different
frequencies as well.
(e) These tone components which contain the PCM samples of a particular frequency or group of
frequencies reside in a bank of memory called tone memory.
(f) Each bank of this tone memory consist s one tone component.
(g) When a tone consists of more than one tone component the second tone component may be
just silence (regarded as inaudible d. c. signal).
(h) If in a tone (like RBT) there is one tone component followed by silence then the tone is said to
have cadence.
4.6 Signal Processor (SP) card:
Signal processor exchanges signalling information between Termination cards and Terminal
interface controller. The SP card acts as an interface between the terminal cards and Terminal
interface controller cum Switching Network (TIC / SN) card. This interface is primarily for
supervisory, control and data signal.
1. Main functions-
The Signal processor card performs the following functions:
(a) Receiving supervisory signals such as on - hook / off – hook/ hook switch flash
and decadic (dial) pulses from termination and also for transient validation (noise
rejection).
(b) Controlling ringing towards subscriber and providing automatic ring trip when the
called subscriber goes off - hook.
(c) Controlling metering signals.
(d) Recognising incoming ring from incoming junction calls.
(e) Controlling out pulsing towards junction calls.
(f) Channel associated signalling on digital trunks.

56. 4.7 Subscriber line card (SLC) or line circuit card (LCC):
Line circuit card is one of the termination cards and It is the first link in the chain of cards
comprising the exchange.
Line circuit card (LCC) is the direct interface between the exchange and subscriber. Each card has 8
identical circuits on which it receives 8 pairs of subscriber telephone wires. Each of these circuits
does the following function.
1. MAIN FUNCTIONS-
1. D.C feed to subscriber for signalling and energising handset microphone.
2. Detects the status of the corresponding subscriber telephone handset i.e. on –
hook (idle or ringing) or off – hook (call initialisation or ring trip).
3. Enables the voice of the subscriber to reach a point within the exchange for
onward Transmission to the called party or vice-versa.
4. Through control logic, subscriber line card (SLC) performs a diagnostic check on
the basic health of the card.
5. It has provision to operate from any of the two sets of the input signals i.e. copy
– 0 or copy - 1(copy selection).
6. The subscriber line card communicates with the Terminal Interface Controller &
Switching Network (TIC / SN) for voice switching.
7. The subscriber line card communicates with signal processor card (SPC) for
Signalling data.
8. Operates Test Access Rely for a particular subscriber line.
The basic function of Line Circuit Card (Termination cards) is collectively termed as BORSCHT
an acronym for –
B - Battery Feed.( -48v, 35 mA)
O - Over Voltage Protection.
R - Ringing.
S - Supervision.
C - Coding & Decoding
H - Hybrid Conversion ( 2 / 4 wire conversion)
T - Testing.

57. CONCLUSION
Indian Railways, as an organization is a very vast center of
telecommunication in itself. Today the telecommunicating world is getting its
roots, grabbing the new era more firmly. We think that our training was an success
and we think that Indian Railways was an excellent training institute for inquisitive
emerging engineers. In Indian Railways, training is given to engineering aspirant
desiring to secure future in the dynamic world of Telecommunication.
The main achievements of the training at Indian Railways are that we got
familiar with the latest technologies and principles of networking. The main
achievement could be said to get knowledge about recent technologies of LAN.
We got experience as to how to organize the things. After the completion of the
training we consider ourselves capable of facing any other challenge of that type.
The training at Indian Railways cultivated the zeal of inquisitiveness and the
excitement to know more than more about this field in limited duration.