NORTH WESTERN RAILWAYS
Optical fiber can be used as a medium for telecommunication
and networking because it is flexible and can be bundled as
Optical fiber can be used to supply a low level of power (around
one watt) to electronics situated in a difficult electrical
This method is most commonly used in front sights.
An optical fiber doped with certain rare earth elements such as
erbium can be used as the gain medium of a laser of optical
Both wavelengths of light are transmitted through the doped
fiber, which transfers energy from the second pump wavelength
to the signal wave.
Principle of operation
An optical fiber is a cylindrical dielectric waveguide
(nonconducting waveguide) that transmits lights along its axis,
by the process of total internal reflection.
The fiber consists of a core surrounded by a cladding layer,
both of which are made of dielectric material.
To confine the optical signal in the core, the refractive index of
the core must be greater than that of the cladding.
The boundary between the core and cladding may either be
abrupt, in step-index fiber, or gradual, in graded-index fiber.
Total internal reflection
When light traveling in a dense medium hits a boundary at a
steep angle (lager than the “critical angle” for the boundary), the
light will be completely reflected.
In simpler terms, there is a maximum angle form the fiber axis
at which light may enter the fiber so that I tit will propagate, or
travel, in the core of the fire, the since of this maximum angle is
the numerical aperture (NA) of the fiber.
Optical fiber types.
In 1933 a French scientist established communication across the
English Channel with an I Watt transmitter operating on 170 um
This he called " It is multi channel directional narrow band radio
relay system. Microwave MICRO" .
The Microwave frequency spectrum is usually taken to extend from
1 GHz to 1000 GHz. The electromagnetic wave spectrum of interest
Ultra high frequency (UHF) from 300 to 3000 MHz
Super high frequency (SHF) 3 to 30 GHz
Externally high frequency (EHF) 30 to 300 GHz
Microwave communication is known as a form of "line of sight"
communication, because there must be nothing obstructing the
transmission of data between these towers for signals to be
properly sent and received.
FEATURES OF DIGITAL MICROWAVE
It is having 100% hot stand by system with space diversity
The modulation is QPSK (quadrature phase shift keying).
Independent switching for TX and Rx direction.
To avoid overreach interference 4 or 6 frequency plan is used.
The reliability of circuit is very high i.e. efficiency is 99.999%.
Computerized passenger reservation system is the most useful
facility, which enhances the image of Indian railways in public.
Initially it was installed in Delhi by Criss and for western and
central railways a common super computer is installed CSTN
and the trains of both railways are programmed on this
When more than one terminal is required at a place then another
8 terminal modem Mux called CODEC is used.
In PRS there is only one set of computer in which all the
information regarding the main coaches, reservation fare, status
Modulation :- Process of superimposing original signal on carrier signal is b/a
Multiplexing :- Converting multi input signal into one output signal is known as
MODEM :- It is the combination of modulator and demodulator. Actually multiplexer
is also a device which itself also as multiplexing and demultiplexing.
It is analogous to modem the help of modulation analog data is converted into is
converted into analog data.
PGM:- Pluse code modulation. It is the process of tranferring the digital data
through the fiber. The analog data is first converted into digital data. (sampling,
Filtering , Quantization)
In early days the officials works in railway was done on the
paper like information to department or any other instruction for
the employee was given only in the written way on the paper.
The networks used in railway are
FOIS : Freight operation and information system
Indian railways have decided to setup their own Corporate
Wide Information system called Railnet to provide computer
connectivity between Zonal railways, production units.
Composition of Railnet
Intra-net is an internal network of Indian railway allowing the
railway officer and staff to communicate on this digitzed
Internet allows users to get into a global communication and
global pool of knowledge advertisement and entertainment
through www ( World Wide Web) in a secured manner. It is
operated by railway board.
The main server is attached to all station and exchanges with
help of interface protocol & MUX.
The railway department has taken 2 MB stream of MTNL.