A

Industrial Training REPORT ON

SIGNAL AND TELECOMMUNICATION

UNDERTAKEN AT

NORTH EASTERN RAILWAY

GORAKHPUR

Submitted in partial fulfillment of the

Requirement for the award of the degree of

BACHELOR OF TECHNOLOGY

IN

ELECTRICAL AND ELECTRONICS ENGINEERING

SUBMITTED BY: - SUBMITTED TO:-

SAURABH PARASHAR MR.AMIT KUMAR

(ROLL NO. -10060108031) (ASST. PROFESSOR)

DEPARTMENT OF ELECTRICAL ENGINEERING

COLLEGE OF ENGINEERING ROORKEE (UTTRAKHAND TECHNICAL UNIVERSITY,DEHRADUN)

SESSION 2013-2014

CERTIFICATE

This is to certify that SAURABH PARASHAR, a III year student of Electrical

and Electronics branch from College of Engineering Roorkee had completed a

4week training with Northern Eastern Railways (NER) in the following

modules:-

1. OPTICAL FIBRE CABLE EQUIPMENT AND CABLES

2. ELECTRONIC EXCHANGE

3. NETWORKING

During this period he showed keen interest in every field. We wish him success for

his future.

Date: - 11 July 2013

CONTENTS

1. ACKNOWLEDGEMENT

2. ABSTRACT

3. INTRODUCTION

4. HISTORY

5. STRUCTURE

6. ZONAL RAILWAYS AND HEADQUARTER

7. COMMUNICATION

8. OPTICAL FIBRE CABLE EQUIPMENT AND CABLES

9. ELECTRONIC EXCHANGE

10. NETWORKING

11. CONCLUSION

12. REFERENCES

ACKNOWLEDGEMENT

Behind the completion of any successful work there lies the contribution of not one but many

individuals who may have directly or indirectly contributed to it.

First and foremost I am grateful to the management of NORTH EASTERN RAILWAY,

GORAKHPUR for providing me the opportunity to undertake my “Summer Industrial

Training” in the organization. I specially convey my thanks to all the staff members for their

precious guidance during our training and in completion of this project. I feel privileged to

express my deep regards and gratitude to all the Engineers and staffs of MICROWAVE

CENTRE, N.E RLY, GORAKHPUR and SIGNAL WORKSHOP, N.E RLY,

GORAKHPUR.

I am thankful to all my teachers who have best owed upon me their knowledge and have

been guiding light throughout my course. They have cast an indelible impression on my

existence.

I am much indent to my friends whose moral support always inspired me to come out with

the best. It’s great pleasure to extend my heartfelt thanks to everybody who helped me through

the successful completion of my training.

The acknowledgement would be incomplete if I fail to express deep sense of my obligation

and reverence to my parents without whom this work would not have seen the light of the day.

SAURABH PARASHAR

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.

HISTORY

The first railway on Indian sub-continent ran over a

stretch of 21 miles from Bombay to Thane.

The idea of a railway to connect Bombay with

Thane, Kalyan and with the Thal and Bhore Ghats

inclines first occurred to Mr. George Clark, the Chief

Engineer of the Bombay Government, during a visit to

Bhandup in 1843.

The formal inauguration ceremony was performed on 16th April 1853, when 14 railway

carriages carrying about 400 guests left Bori Bunder at 3.30 pm "amidst the loud applause of a

vast multitude and to the salute of 21 guns."

The first passenger train steamed out of Howrah station

destined for Hooghly, a distance of 24 miles, on 15th

August, 1854. Thus the first section of the East Indian

Railway was opened to public traffic, inaugurating the

beginning of railway transport on the Eastern side of the

sub-continent.

In south the first line was opened on Ist July, 1856 by the

Madras Railway Company. It ran between Veyasarpandy and Walajah Road (Arcot), a distance

of 63 miles. In the North a length of 119 miles of line was laid from Allahabad to Kanpur on 3rd

March 1859. The first section from Hathras Road to Mathura Cantonment was opened to traffic

on 19th October, 1875.

These were the small beginnings which is due course developed into a network of railway lines

all over the country. By 1880 the Indian Railway system had a route mileage of about 9000

miles.

STRUCTURE

Indian Railways has one of the largest and busiest rail networks in the world, transporting over

18 million passengers and more than 2 million tons of freight daily. It is the world's largest

commercial or utility employer, with more than 1.4 million employees. The railways traverse the

length 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, IR owns over 200,000 (freight) wagons,

50,000 coaches and 8,000 locomotives. Indian Railways operates about 9,000 passenger trains

and transports 18 million passengers daily across twenty-eight states and one union territory.

Sikkim, Arunachal Pradesh and Meghalaya are the only states not connected by rail. The

passenger division is the most preferred form of long distance transport in most of the country.

Indian Railways is divided into zones, which are further sub-divided into divisions. The number

of zones in Indian Railways increased from six to eight in 1951, nine in 1952, and finally 16 in

2003. Each zonal railway is made up of a certain number of divisions, each having a divisional

headquarters. There are a total of sixty-seven divisions.

Each of the sixteen zones, as well as the Kolkata Metro, is headed by a General Manager (GM)

who reports directly to the Railway Board. The zones are further divided into divisions under the

control of Divisional Railway Managers (DRM). The divisional officers of engineering,

mechanical, electrical, signal & telecommunication, accounts, personnel, operating, commercial

and safety branches report to the respective Divisional Manager and are in charge of operation

and maintenance of assets. Further down the hierarchy tree are the Station Masters who control

individual stations and the train movement through the track territory under their stations'

administration. (See fig.)

RAILWAY BOARD

ZONAL RAILWAYS

DIVISIONS

ENG

G.

OPERAT

AING

PERSONNE

L ACC. SAFE

TY

MEC

H

ELEC

T

S&T COM

M

ZONAL RAILWAYS AND HEADQUARTER

Sl.

No Name Abbr.

Date

Established Headquarters Divisions

1. Central CR November 5,

1951 Mumbai

Mumbai, Bhusawal, Pune, Solapur,

Nagpur

2. East Central ECR October 1,

2002 Hajipur

Danapur, Dhanbad, Mughalsarai,

Samastipur, Sonpur

3. East Coast ECoR April 1, 2003 Bhubaneswar Khurda Road, Sambalpur,

Visakhapatnam

4. Eastern ER April, 1952 Kolkata Howrah, Sealdah, Asansol, Malda

5. North

Central NCR April 1, 2003 Allahabad Allahabad, Agra, Jhansi

6. North

Eastern NER 1952 Gorakhpur Izzatnagar, Lucknow, Varanasi

7. North

Western NWR

October 1,

2002 Jaipur Jaipur, Ajmer, Bikaner, Jodhpur

Northeast

Frontier NFR 1958 Guwahati

Alipurduar, Katihar, Lumding, Rangia,

Tinsukia

9. Northern NR April 14,

1952 Delhi

Delhi, Ambala, Firozpur, Lucknow,

Moradabad

10. South

Central SCR

October 2,

1966 Secunderabad

Secunderabad, Hyderabad, Guntakal,

Guntur, Nanded, Vijayawada

11. South East

Central SECR April 1, 2003 Bilaspur, CG Bilaspur, Raipur, Nagpur

12. South

Eastern SER 1955 Kolkata

Adra, Chakradharpur, Kharagpur,

Ranchi

13. South

Western SWR April 1, 2003 Hubli Hubli, Bengaluru, Mysore

14. Southern SR April 14,

1951 Chennai

Chennai, Madurai, Palakkad, Salem,

Tiruchchirappalli, Thiruvanathapuram

15. West

Central WCR April 1, 2003 Jabalpur Jabalpur, Bhopal, Kota

16. Western WR November 5,

1951 Mumbai

Mumbai Central, Vadodara, Ratlam,

Ahmedabad, Rajkot, Bhavnagar

COMMUNICATION

Today, it would be difficult for us to imagine life without the telephone. World-wide, there are

some 750 million telephone connections in use and the number of Internet users has exploded in

the last few years. By the year 2010, according to a forecast from Nortel, there will be almost

475 million Internet users and the number of services provided will also grow rapidly.

To control the working of employers and to ensure the proper running of trains, we need fast and

reliable means of communication. To ensure this we have “SIGNAL &

TELECOMMUNICATION” department. They provide path and sources (Equipments) to

communicate. Their work is to provide the line and maintain it.

Railway communication provides uninterrupted motion of trains. Due to faster means of

communication there is increase in the efficiency and greater control. To communicate we

require some media, which carry our signal. In past, railway use iron wires, copper wires or

aluminum wires for signal propagation. Now, a day we railway use Microwave, Quad cable,

Optical Fiber cable & satellite communication.

The explosion in demand for network bandwidth is largely due to the growth in data traffic,

specifically Internet Protocol (IP). Leading service providers report bandwidths doubling on their

backbones about every six to nine months. This is largely in response to the 300 percent growth

per year in Internet traffic, while traditional voice traffic grows at a compound annual rate of

only about 13 percent.

OFC EQUIPMENT AND CABLES

OPTICAL FIBRE EQUIPMENT

STM-1 Optical to STM-1 Electrical Converter

Valiant VCL-STM-1 Optical to STM-1 Electrical converter provides a simple and cost-effective

conversion between STM-1 optical interfaces to STM-1 electrical interface.

VCL-STM-1 Optical to STM-1 Electrical converter is interface conversion equipment supplied

with one STM-1 electrical interface and one STM-1 optical interface.

VCL-STM-1 Optical to STM-1 Electrical converter is a compact solution housed in a 19" rack

1U high, which can be placed on the desktop or installed in a standard 19 inch rack.

This unit offers dual (1+1) power supply options. Options for the power supply to the

equipment include:

1. Dual DC -48V Inputs (range -18V DC to -72V DC)

2. Dual AC Inputs (range 110V AC to 240V AC, 50 / 60Hz)

STM-1 Optical to STM-1 Electrical converters converter complies with ITU-T and the

relevant SDH specifications. The rear panel includes power socket and alarm output

terminal interface.

Features and Highlights

1+0 STM-1 Optical to STM-1 Electrical

1+1 STM-1 Optical to STM-1 Electrical options available

SFP based design. Provides field removable / upgradeable optical SFPs

Short haul (1310nm), long haul (1550nm) and multi-mode (850nm) optical SFP

modules

Provides low cost STM-1 Optical to STM-1 Electrical conversion

Management options:

Serial RS232 Port (COM Port)

10/100 BaseT Remote Management over LAN Telnet

10/100 BaseT Telnet over TCP-IP Network

SNMP V2

USB interface

Network Management System (NMS)

High reliability, complies to ITU-T G.703 and G.957

State-of-the-art design, ensure normal working under difficult environments

Supports local and remote loop-back on electrical or optical interface for system

diagnostics.

Simple operation and maintenance

Compact design and low power consumption.

75 Ohms compliant with ITU-T G.703 and Telcordia GR-253 155Mbps electrical interfaces

(BNC connector).

ITU-T G.783 compatible loss of signal detects.

Handles over 12.7dB of cable loss.

Duplex LC optical interface.

Hot-pluggable.

Supports DDM function for read back of transmit and received optical power.

Class 1 laser safety.

Compliant with ITU-T G.957 STM-1.

Management options

Serial RS232 Port (COM Port).

10/100 BaseT Remote Management over LAN Telnet.

10/100 BaseT Telnet over TCP-IP Network.

SNMP V2.

USB interface.

Network Management System (NMS).

INTRODUCTION

The demand for high-capacity long-haul Signal & telecommunication systems is increasing at a

steady rate, and is expected to accelerate in the next decade. At the same time, communication

networks which cover long distances and serve large areas with a large information capacity are

also in increasing demand. To satisfy the requirements on long distances, the communication

channel must have a very low loss. On the other hand, a large information capacity can only be

achieved with a wide system bandwidth which can support a high data bit rate (> Gbit/s).

Reducing the loss whilst increasing the bandwidth of the communication channels is therefore

essential for future telecommunications systems. Of the many different communication channel

available optical fiber proved to the most promising due to its low attenuation, low losses and

various other advantages over twisted cables and other means of transmission.

Communication between stations and signalmen is done through telephone. In some places, IR

still uses twisted pair cables and elderly stronger exchanges. Drivers and guards were equipped

with VHF radio systems in 1999 to communicate with each other and with station masters.

OPTICAL FIBER COMMUNICATION SYSTEM

A thin glass strand designed for light transmission. A single hair-thin fiber is capable of

transmitting trillions of bits per second. In addition to their huge transmission capacity, optical

fibers offer many advantages over electricity and copper wire. Light pulses are not affected by

random radiation in the environment, and their error rate is significantly lower. Fibers allow

longer distances to be spanned before the signal has to be regenerated by expensive "repeaters."

Fibers are more secure, because taps in the line can be detected, and lastly, fiber installation is

streamlined due to their dramatically lower weight and smaller size compared to copper cables.

Optical fiber v/s copper cable

The optical fiber acts as a low loss, wide bandwidth transmission channel. A light source is

required to emit light signals, which are modulated by the signal data.

To enhance the performance of the system, a spectrally pure light source is required. Advances

in semiconductor laser technology, especially after the invention of double hetero structures

(DH), resulted in stable, efficient, small-sized and compact semiconductor laser diodes (SLDs).

Using such coherent light sources increases the bandwidth of the signal which can be transmitted

in a simple intensity modulated (IM) system.

Other modulation methods, such as phase shift keying (PSK) and frequency-shift keying (FSK),

can also be used. These can be achieved either by directly modulating the injection current to the

SLD or by using an externals electro or acousto-optic modulator.

ORIGIN AND CHARACTERISTICS OF OPTICAL FIBER

In the late 1970s and early 1980s, telephone companies began to use fibers extensively to rebuild

their communications infrastructure. According to KMI Corporation, specialists in fiber optic

market research, by the end of 1990 there were approximately eight million miles of fiber laid in

the U.S. (this is miles of fiber, not miles of cable which can contain many fibers). By the end of

2000, there were 80 million miles in the U.S. and 225 million worldwide. Copper cable is

increasingly being replaced with fibers for LAN back bones as well, and this usage is expected to

increase substantially.

Pure Glass

An optical fiber is constructed of a transparent core made of nearly pure silicon dioxide (SiO2),

through which the light travels. The core is surrounded by a cladding layer that reflects light,

guiding the light along the core. A plastic coating covers the cladding to protect the glass surface.

Cables also include fibers of Kevlar and/or steel wires for strength and an outer sheath of plastic

or Teflon for protection. ro or acousto-optic modulator.

Enormous Bandwidth

For glass fibers, there are two "optical windows" where the fiber is most transparent and

efficient. The centers of these windows are 1300 nm and 1550 nm, providing approximately

18,000GHz and 12,000GHz respectively, for a total of 30,000GHz. This enormous bandwidth is

potentially usable in one fiber. Plastic is also used for short-distance fiber runs, and their

transparent windows are typically 650 nm and in the 750-900 nm range.

Single mode and Multimode

There are two primary types of fiber. For intercity cabling and highest speed, single mode fiber

with a core diameter of less than 10 microns is used. Multimode fiber is very common for short

distances and has a core diameter from 50 to 100 microns. See laser, WDM, fiber optics glossary

and cable categories.

OPERATION OF OPTICAL FIBER

In an optical fiber, a refracted ray is one that is refracted from the core into the cladding.

Specifically a ray having direction such that where r is the radial distance from the fiber axis,

φ(r) is the azimuthally angle of projection of the ray at on the transverse plane, θ(r )is the angle

the ray makes with the fiber axis, n (r ) is the refractive index at r, n (a ) is the refractive index at

the core radius, a . Refracted rays correspond to radiation modes in the terminology of mode

descriptors.

For the fiber to guide the optical signal, the refractive index of the core must be slightly higher

than that of the cladding. In different types of fibers, the core and core-cladding boundary

function slightly differently in guiding the signal. Especially in single-mode fibers, a significant

fraction of the energy in the bound mode travels in the cladding.

The light in a fiber-optic cable travels through the core (hallway) by constantly bouncing from

the cladding (mirror-lined walls), a principle called total internal reflection. Because the cladding

does not absorb any light from the core, the light wave can travel great distances. However, some

of the light signal degrades within the fiber, mostly due to impurities in the glass. The extent that

the signal degrades depends on the purity of the glass and the wavelength of the transmitted light

(for example, 850 nm = 60 to 75percent/km; 1,300 nm = 50 to 60 percent/km ; 1,550 nm is

greater than 50 percent/km). Some premium optical fibers show much less signal degradation --

less than 10percent/km at 1,550 nm.

A FIBER-OPTIC RELAY SYSTEM

To understand how optical fibers are used in communication systems, let's look at an example

from a World War II movie or documentary where two naval ships in a fleet need to

communicate with each other while maintaining radio silence or on stormy seas. One ship pulls

up alongside the other. The captain of one ship sends a message to a sailor on deck. The sailor

translates the message into Morse code (dots and dashes) and uses a signal light (floodlight with

a Venetian blind type shutter on it) to send the message to the other ship. A sailor on the deck of

the other ship sees the Morse code message, decodes it into English and sends the message up to

the captain. Now, imagine doing this when the ships are on either side of the ocean separated by

thousands of miles and you have a fiber-optic communication system in place between the two

ships.

Fiber-optic relay systems consist of the following:

TRANSMITTER - Produces and encodes the light signals

OPTICAL FIBER - Conducts the light signals over a distance

OPTICAL REGENERATOR - May be necessary to boost the light signal (for long distances)

OPTICAL RECEIVER - Receives and decodes the light signals

TRANSMITTER - The transmitter is like the sailor on the deck of the sending ship. It receives

and directs the optical device to turn the light "on" and "off" in the correct sequence, thereby

generating a light signal.

The transmitter is physically close to the optical fiber and may even have a lens to focus the light

into the fiber. Lasers have more power than LEDs, but vary more with changes in temperature

and are more expensive. The most common wavelengths of light signals are 850 nm, 1,300 nm,

and 1,550 nm (infrared, non-visible portions of the spectrum).

Optical Regenerator

As mentioned above, some signal loss occurs when the light is transmitted through the fiber,

especially over long distances (more than a half mile, or about 1 km) such as with undersea

cables. Therefore, one or more optical regenerators is spliced along the cable to boost the

degraded light signals.

An optical regenerator consists of optical fibers with a special coating (doping). The doped

portion is "pumped" with a laser. When the degraded signal comes into the doped coating, the

energy from the laser allows the doped molecules to become lasers themselves. The doped

molecules then emit a new, stronger light signal with the same characteristics as the incoming

weak light signal. Basically, the regenerator is a laser amplifier for the incoming signal.

Optical Receiver

The optical receiver is like the sailor on the deck of the receiving ship. It takes the incoming

digital light signals, decodes them and sends the electrical signal to the other user's computer, TV

or telephone (receiving ship's captain). The receiver uses a photocell or photodiode to detect the

light.

USES OF OPTICAL FIBER

The optical fiber can be used as a medium for telecommunication and networking because it is

flexible and can be bundled as cables. Although fibers can be made out of either transparent

plastic or glass, the fibers used in long-distance telecommunications applications are always

glass, because of the lower optical absorption. The light transmitted through the fiber is confined

due to total internal reflection within the material. This is an important property that eliminates

signal crosstalk between fibers within the cable and allows the routing of the cable with twists

and turns. In telecommunications applications, the light used is typically infrared light, at

wavelengths near to the minimum absorption wavelength of the fiber in use.

Core - Thin glass center of the fiber where the light travels.

Cladding- Outer optical material surrounding the core that reflects the light back into the core.

Buffer coating - Plastic coating that protects the fiber from damage and moisture.

Fibers are generally used in pairs, with one fiber of the pair carrying a signal in each direction,

however bidirectional communications is possible over one strand by using two different

wavelengths (colors) and appropriate coupling/splitting devices.

Fibers, like waveguides, can have various transmission modes. The fibers used for long-distance

communication are known as single mode fibers, as they have only one strong propagation

mode. This results in superior performance compared to other, multi-mode fibers, where light

transmitted in the different modes arrives at different times, resulting in dispersion of the

transmitted signal. Typical single mode fiber optic cables can sustain transmission distances of

80 to 140 km between regenerations of the signal, whereas most multi-mode fiber has a

maximum transmission distance of 300 to 500 meters.

Single mode equipment is generally more expensive than multi-mode equipment. Fibers used in

telecommunications typically have a diameter of 125 μm. The transmission core of single-mode

fibers most commonly has a diameter of 9 μm, while multi-mode cores are available with 50 μm

or 62.5 μm diameters.

Because of the remarkably low loss and excellent linearity and dispersion behavior of single-

mode optical fiber, data rates of up to 40 gigabits per second are possible in real-world use on a

single wavelength. Wavelength division multiplexing can then be used to allow many

wavelengths to be used at once on a single fiber, allowing a single fiber to bear an aggregate

bandwidth measured in terabits per second.

Modern fiber cables can contain up to a thousand fibers in a single cable, so the performance of

optical networks easily accommodate even today's demands for bandwidth on a point-to-point

basis. However, unused point-to-point potential band width does not translate to operating

profits, and it is estimated that no more than 1% of the optical fiber buried in recent years is

actually 'lit'.

Modern cables come in a wide variety of sheathings and armor, designed for applications such as

direct burial in trenches, installation in conduit, lashing to aerial telephone poles, submarine

installation, or insertion in paved streets. In recent years the cost of small fiber-count pole

mounted cables has greatly decreased due to the high Japanese and South Korean demand for

Fiber to the Home (FTTH) installations.

Recent advances in fiber technology have reduced losses so far that no amplification of the

optical signal is needed over distances of hundreds of kilometers. This has greatly reduced the

cost of optical networking, particularly over undersea spans where the cost reliability of

amplifiers is one of the key factors determining the performance of the whole cable system. In

the past few years several manufacturers of submarine cable line terminal equipment have

introduced upgrades that promise to quadruple the capacity of older submarine systems installed

in the early to mid-1990s.

ADVANTAGES OF OPTICAL FIBER

Low loss, so repeater-less transmission over long distances is possible

Large data-carrying capacity (thousands of times greater, reaching speeds of up to 3TB/s).

Immunity to electromagnetic interference, including nuclear electromagnetic pulses (but can

be damaged by alpha and beta radiation).

No electromagnetic radiation; difficult to eavesdrop.

High electrical resistance, so safe to use near high-voltage equipment or between areas with

different earth potentials.

Low weight Signals contain very little power.

APPLICATIONS OF OPTICAL FIBER

Fibers can be used as light guides in medical and other applications where bright light

needs to be brought to bear on a target without a clear line-of-sight path.

Optical fibers can be used as sensors to measure strain, temperature, pressure and other

parameters.

Bundles of fibers are used along with lenses for long, thin imaging devices called

endoscopes, which are used to view objects through a small hole. Medical endoscopes are

used for minimally invasive exploratory or surgical procedures (endoscopy). Industrial

endoscopes (see fiberscope or bore scope) are used for inspecting anything hard to reach,

such as jet engine interiors.

In some high-tech buildings, optical fibers are used to route sunlight from the roof to

other parts of the building.

Optical fibers have many decorative applications, including signs and art, articifal

Christmas tree & lighting.

ELECTRONIC EXCHANGE

Telephone exchange

A telephone operator manually connecting calls with cord pairs at a telephone switchboard. In

the field of telecommunications, 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 inside plant equipment including telephone switches, which make telephone calls

"work" in the sense of making connections and relaying the speech information.

The term exchange area can be used to refer to an area served by a particular switch, but is

typically known as a wire center in the US telecommunications industry. The exchange code or

Central Office Code refers to the first three digits of the local number (NXX). It is sometimes

confused with the area code (NPA). In the United States, local exchange areas together make up

a legal entity called local access and transport areas (LATA) under the Modification of Final

Judgment (MFJ).

Manual service exchanges

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. Most urban exchanges were common-

battery, meaning that the central office provided power for the telephone circuits, as is the

case today. In common-battery systems, the pair of wires from a subscriber's telephone to

the switch (or manual exchange) carries -48VDC (nominal) from the telephone company

end, across the conductors. The telephone presents an open circuit when it is on-hook or

idle. When the subscriber goes off-hook, the telephone puts a DC resistance short across

the line. In manual service, this current flowing through the off-hook telephone flows

through a relay coil actuating a buzzer and lamp on the operator's switchboard. The

buzzer and lamp would tell an operator the subscriber was off-hook (requesting service).

In the largest U.S. cities, it took many years to convert every office to automatic

equipment, such as panel switches. During this transition period, it was possible to dial a

manual number and be connected without requesting an operator's assistance. This was

because the policy of the Bell System was that customers should not need to know

whether they were calling a manual or automated office. If a subscriber dialed a manual

number, an inward operator would answer the call, see the called number on a display

device, and manually connect the call. For instance, if a customer calling from TAylor

4725 dialed a manual number, Adams 1233, the call would go through, from the

subscriber's perspective, exactly as a call to Lennox 5813, in an automated exchange.

In contrast to the common-battery system, smaller towns with manual service often had

magneto, or crank, phones. Using a magneto set, the subscriber turned a crank to generate

ringing current, to gain the operator's attention. The switchboard would respond by

dropping a metal tab above the subscriber's line jack and sounding a buzzer. Dry cell

batteries (normally two large "No 6" cells) in the subscriber's telephone provided the DC

power for conversation.

Magneto systems were in use in one American small town, Bryant Pond, Woodstock,

Maine as late as 1983. In general, this type of system had a poorer call quality compared

to common-battery systems.

Many small town magneto systems featured party lines, anywhere from two to ten or

more subscribers sharing a single line. When calling a party, the operator would use a

distinctive ringing signal sequence, such as two long rings followed by one short.

Everyone on the line could hear the rings, and of course could pick up and listen in if

they wanted. On rural lines which were not connected to a central office (thus not

connected to the outside world), subscribers would crank the correct sequence of rings to

reach their party.

Circuit Diagram

The analogue circuitry comprises the following parts:

Call sensor

Originating loop

Destination loop

Transmission Bridge

Tone generator

Ring Trip

Call sensor

When the exchange is idle, power is applied to the call sensor via a TLP598G photo-relay. The

sensor comprises 8 CNX35U opto-isolators - one for each line. When an extension is lifted "off-

hook", its associated opto-isolator asserts a sense line. If only one sense line is asserted, the

controller latches the binary code of the originating extension and initiates a call. The call sensor

is powered-down until the end of the call.

Originating Loop

The calling line is connected to the originating loop by an opto-triac. Loop current flows through

transformer T1 secondary, and through the CNX35U loop status opto-isolator which detects

dialing pulses and, ultimately, hang-up.

A small time delay is allowed for things to settle down before dial tone is delivered to the caller

via the primary of transformer T1. If the loop is not closed at the end of the time delay, the

exchange reverts to the idle state.

Destination loop

The called extension is connected to the destination loop by an opto-triac. There are two paths

through the loop: for DC only via transformer T2 and a TLP598G photo-relay; and for AC via

the AC ringing generator and a TLP3043 opto-triac. The paths are switched alternately

producing the required ring-ring effect interspersed with silence. The 598 and 3043 light emitting

diodes are connected back-to-back as a safety interlock. The TLP3043 contains a zero-crossing

circuit to ensure a clean switch.

Ring Trip

The ringing voltage applied to the line is that of the ringing generator plus a DC offset. The

average voltage equals the DC supply. Only AC can flow during ringing because telephone bells

are AC coupled. Answering creates a DC path through the telephone allowing DC to flow.

The 47-ohm resistor samples the line current. The voltage across it is low-pass filtered to

attenuate the AC component. When the call is answered, the DC component operates the BC640

PNP transistor which asserts the Trip input to the controller. A high voltage PNP transistor is

required. The BC640 has a VCEO of 80V.

Transmission Bridge

The secondaries of transformers T1 and T2, and the 2μ2 coupling capacitor form the

transmission bridge. The transformers act as low frequency chokes, passing DC to the carbon

microphones whilst presenting high impedance to audio frequencies.

The transformers were salvaged from an old cordless telephone. Similar types can also be found

in modems and other mains-powered telephone appliances.

The primary of T1 is connected to the tone generator. The primary of T2 could be used for an

outside line facility.

Tone generator

The tone generator takes up approximately one quarter of the analogue board area. It was felt

that high quality sinusoidal tones were worth having. Square waves and /or 50Hz mains hum

sound unpleasant and are not user-friendly. This little exchange sounds like the real thing!

An LM324 quad op-amp generates three independent sine waves. The fourth amplifier is used as

a supply splitter to generate a 2.5V virtual earth. Wien bridge oscillators are used with a simple

diode shaping circuit to control the amplitude. The resultant harmonic distortion is minimized by

adjustment of the presets and by subsequent low pass filtering.

The tones are coupled to the originating loop via transformer T1. An emitter follower drives the

primary. The required tone combination is selected using a 4016 quad bilateral switch. To

prevent clicks, the 2.5V virtual earth is connected in the gaps between rings. When all the

switches are off, the emitter follower goes tri-state and thus does not load the speech path.

Controller

The controller, comprising 3 programmable logic devices (PLDs) plus discrete HCMOS,

occupies an entire euro card. RC delays and Schmitt triggers are used for timing. I would use a

single chip micro-controller if I were making more than one of these!

The Atmel ATF16V8B PLDs were programmed using the Atmel version of WinCUPL

downloaded from www.atmel.com for free.

IC INSIDE

NETWORKING

RAIL NET

The Indian Railways is Asia's largest and the world's second largest rail network. Adopting e-

Governance in right earnest and to reap the benefit of IT explosion, Indian Railways have

established a 'Corporate Wide Information System' (CWIS) called RAILNET.

It provides smooth flow of information on demand for administrative purposes, which would

enable taking quicker and better decisions?

Realizing the important role that information plays in customer services and in railways

operations, IR had embarked on its computerization program. IR developed dedicated skeletal

communication network, as a basic requirement for train operation.

After the early introduction of basic computer applications e.g. Pay rolls, Inventory Control and

Operating Statistics, Railways went for deployment of computers for productivity improvement

through building up operational databases.

IVRS

(INTERACTIVE VOICE RESPONSE SYSTEM)

Interactive voice response (IVR) is a technology that allows a computer to interact with

humans through the use of voice and DTMF keypad inputs.

In telecommunications, IVR allows customers to interact with a company’s database via a

telephone keypad or by speech recognition, after which they can service their own inquiries by

following the IVR dialogue. IVR systems can respond with prerecorded or dynamically

generated audio to further direct users on how to proceed. IVR applications can be used to

control almost any function where the interface can be broken down into a series of simple

interactions. IVR systems deployed in the network are sized to handle large call volumes. IVR

technology is also being introduced into automobile systems for hands-free operation. Current

deployment in automobiles revolves around satellite navigation, audio and mobile phone

systems.

It has become common in industries that have recently entered the telecommunications industry

to refer to an automated attendant as an IVR. The terms, however, are distinct and mean different

things to traditional telecommunications professionals, whereas emerging telephony and VoIP

professionals often use the term IVR as a catch-all to signify any kind of telephony menu, even a

basic automated attendant. The term voice response unit (VRU) is sometimes used as well.

PRS- PASSENGER RESERVATION SYSTEM

Reserved travel by Indian Railways is facilitated by the Passenger Reservation System (PRS).

PRS provides reservation services to nearly 1.5 to 2.2 million passengers a day on over 2500

trains running throughout the country. The PRS Application CONCERT (Country-wide Network

of Computerized Enhanced Reservation and Ticketing) is the world’s largest online reservation

application, developed and maintained by CRIS. The system currently operates from 5 Data

centers. The server clusters are connected together by a core network that enables universal

terminals across country, through which the travelling public can reserve a berth on any train,

between any pair of station for any date and class.

PRS web site was awarded Web Ratna Platinum Icon Award in year 2009 under Citizen Centric

Service category. PRS application has been awarded by Computer Society of India for best IT

usage in the year 1999. If you have any further questions or suggestions email us at

prs@cris.org.in.

ROUTER

A router is a device that forwards data packets between telecommunications networks, creating

an overlay internetwork. A router is connected to two or more data lines from different networks.

When data comes in on one of the lines, the router reads the address information in the packet to

determine its ultimate destination. Then, using information in its routing table or routing policy,

it directs the packet to the next network on its journey or drops the packet. A data packet is

typically forwarded from one router to another through networks that constitute the internetwork

until it gets to its destination node.[1]

The most familiar type of routers are home and small office routers that simply pass data, such as

web pages and email, between the home computers and the owner's cable or DSL modem, which

connects to the Internet (ISP). However more sophisticated routers range from enterprise routers,

which connect large business or ISP networks up to the powerful core routers that forward data

at high speed along the optical fiber lines of the Internet backbone.

A PICTURE OF ROUTER-BY CISCO