Practical training seminar

Neha Chouhan12EJTEC045

North Western Railway

• North western railway came into existence on October 1, 2002.

• The North Western Railway is one of the sixteen railway zones in India.

•  It comprises four divisions:• Jodhpur• Ajmer• Jaipur• Bikaner

Conti………• This railway comprises a total of 578 stations .

• Covering a total of 5449.29 route km out of which 2575.03 are broad gauge and 2874.23 are metre gauge

Role of Telecom Department in Indian Railways

During my training period I found that it plays a key role

efficient working of train movement and it is heart of system. I cover some of the topics which is very helpful for working of that system. Topics are:

A. ExchangeB. Optical fiber

OFC (optical fiber cable)

•Optical fiber comm. Means information is send the form of light beam from one end to another end .

• In this system a no. of channels is multiplexed and electrical information convert into light beam and transmit to media to reached another end .

• At another end light beam converts in electrical information and getting through demultiplexing process.

Cont…..• An optical fiber is a hair thin cylindrical fiber of

glass or any transparent dielectric medium.

• The fiber which are used for optical communication are wave guides made of transparent dielectrics.

• • Its function is to guide visible and infrared light

over long distances

• Core – central tube of very thin size made up of optically transparent dielectric medium and carries the light form transmitter to receiver. The core diameter can vary from about 5um to 100 um.

• Cladding – outer optical material surrounding the core having reflecting index lower than core. It helps to keep the light within the core throughout the phenomena of total internal reflection.

• Buffer Coating – plastic coating that protects the fiber made of silicon rubber. The typical

diameter of fiber after coating is 250-300 um.

• 24F armored cable are used in Indian Railway.- Normally used for under ground laying

- It consists 6 loose tubes Blue Orange Natural 1 Natural 2 Natural 3 Natural 4

• Each loose tube contains 4 fibers:Blue Orange Green Natural

• OFC have fibers which are long, thin stands made with pure glass about the diameter of a human hair.OFC consists of Core, Cladding

Type of optical fiber cable• Fiber's are three type according to construction :-

1. Step Index fiber:-corer &cladding have uniformly distributed index

2. Graded Index fiber:-Have refractive index varies gradually

• 3.Single mode fiber:-Have very low core dia(8.3 micro meter)

Applications

• In telecommunication field• In space applications• Broadband applications• Computer applications industrial applications • Mining applications• In medical applications• In military applications etc.

EXCHANGE It is a unit where different subscribers are connected according to their

requests through manual, electromechanical or electronic methods.

There are two type of exchange in jodhpur division

1. ISDN EXCHANGE of 1000 lines

2. C-dot EXCHANGES of 128 ports.

ISDN is the electronic exchange .It is installed in HQ DRMOffice and For road side stations they

use the c-dot exchanges according to No of subscribers.NO of such type of exchanges are Nine

installed at different location like junction station that is Merta Road Jn,Degana Jn,Jaisalmer &so

on

Basic Telephony: General Sound signals can not travel much distance in open space.

Sound signals are converted to electrical signals.

Telephony makes use of electrical/radio/light signals to transmit

speech.

A simple Microphone converts sound signals to electrical signals.

A simple Receiver converts electrical signals to sound signals.

A simple telephone consists of a microphone and a receiver.

A conventional telephone connected to a telephone exchange

consists of microphone, receiver, bell and dialing pad

Basic Telephony: General (contd) Bell is for ringing to draw the attention of the called user.

Calling Party: the user who initiates a call.

Called Party: the user who is called upon by someone.

Telephone was invented by Alexander Graham Bell in 1875.

Entire Telephony equipment's are designed for the speech

band i.e., 300 Hz - 3400 Hz. (4 kHz bandwidth)

Lifting the handset of a telephone is called 'Off Hook'.

Replacing the handset normal is called 'On Hook' condition

In Off hook condition current flows in the line.

In On hook condition no current flows in the line.

Exchange senses the condition of the subscriber telephone by

the current flowing in the line.

Main Function of Exchange

Switching: Switches the subscribers as per dialing codes

Signaling: Dialed information is processed and information is

passed accordingly.

Controlling: Call establishment, metering, monitoring,

releasing and diagnostic features are handled.

Functional Blocks of Telephone Exchange

a) MDF All subscriber lines & trunk lines from the different places are terminated on the MDF using crone arrangement and from there they are connected to the Exchange through IDF using protective devices like GD tubes, Fuses & MOVR• MDF is the most suitable place for testing arrangement(b) Card Frame• It contains different slots for placing various types of cards like SLIC

cards, Trunk cards & Conference cards, these cards are different in different types of exchanges

• c) Mother Board• d) Power Supply Panel• It provides power to different cards of the exchange at different voltage

levels. It includes protective devices like fuses etc. • CB with 1 or 3 layers, all the cards are inter connected

Main functional areas in Telephone Exchange

• a) Switching Function• Switching network provides a temporary path for

simultaneous bi-directional speech between i. Two subscribers connected to the same exchange – local

switching ii.Two subscribers connected to the different exchanges –

Trunk switching iii.Pair of trunks towards different exchanges – Transit

switching

• b) Signaling function: Signaling function enables to establish and supervise the calls It is of two types

i. Subscriber signaling: It enables the exchange to identify calling subscriber line, extend dial tone, receive the dialed digits, extend the ringing voltage to the called subscriber, ring back tone to the called subscriber & if the called subscriber is busy extend busy tone to the calling subscriber

• ii. Inter Exchange signaling: It enables to setup, supervise & clear the call between exchanges.

• c) Controlling function: Performs the processing of signal information & controls the switching network.

i. Wired logic control: Pre wiring is done between devices and control, for introduction of new services requires wiring changes.

Types of switching

1. Manual Switching: Connections are made manually for the

subscribers.

2. Circuit Switching: The circuit is exclusively dedicated to the

connected subscribers for the whole duration of the call.

3. Packet Switching: Information is split into small units called

packets and these packets are transmitted.

4. Message Switching: Information is stored and forwarded

according to the availability of the circuit.

Signaling

• A telecom network establishes & releases temporary connections, in accordance with the instructions received from the subscriber lines & inter exchange trunks in the form of various signals.

Types of Signaling

1. Pulse dialing: The make break of the line.

2. DTMF: Dual Tone Multi Frequency signaling, uses

standard universal tones as input signal which are

processed by the exchange.

3. E&M: Earth no earth signaling, used in Trunk circuits

between exchanges.

Tones generated by Exchange. (DT) Dial Tone: Indicates the readiness of the exchange to

accept dialing.

RBT (Ring Back Tone): Indicates called party is ringing.

BT (Busy Tone): Indicates called party is busy.

NUT (Number Unobtainable Tone): Indicates an invalid

number is dialed.

FT (Feature Tone): Indicates a special feature is invoked.

AT (Assurance Tone): Indicates a given command is accepted.