Railway OFC training
Presented by
Sreerup Chowdhury
Introduction
• OFC stands for optical fibre communication which is used in between
railway.
stations for communication purposes.
• RailTel which is behind the OFC development has created state of the
art multimedia telecom network using SDH based transmission
systems.
• The Corporation was formed in Sept 2000 with the objectives to create
nationwide Broadband Telecom and Multimedia Network in all parts of
the country, to modernize Train Control Operation and Safety System of
Indian Railways.
Training Topics
• Optical Fibre.
▫ Advantages, description, additional equipment for handling.
• Digital Multiplexing Hierarchies.
▫ SDH,PDH,STM and PDMUX.
• NMS(Network Management System).
▫ Software based interface designed to control and configure fleximux
equipment.
• Power supply of OFC system.
Advantages of using optical fibre
• Low transmission loss - Resulting in large spacing between repeaters loss in twisted
pair and co-axial cable increases with frequency, whereas; loss in the optical fibre
remains flat over a wide range of frequencies.
• Wide Bandwidth resulting in very Large Channel Capacity.
• Immunity to Electromagnetic and Radio Frequency Interface being insulator no
electric current flows through the fibre and due to this reason fibre neither radiate
nor pick up electromagnetic radiation.
• No Cross Talk - As the signal transmission is by digital modulation, there is no chance
of cross talk in between channels.
• Less prone to theft - As the fibre does not have resale value in the market, optical
fibre cable is not theft prone.
Optical Fibre
• An Optical Fibre is a Types of optical fibres.
long, thin strand • Single-mode step index
made with pure glass • Multi-mode step index
about the diameter of • Multimode graded index
a human hair.
• OFC consists of Core,
Cladding, Buffers and
Jacket as shown in
figure.
Additional equipment
OTDR(Optical Time Domain Reflector)
• OTDR uses a system similar to radar set, It
sends out a light pulse and act on the
reflected light from the fibre.
• The OTDR can continuously measure the
returned power level and hence figure out
the losses on the fibre link.
Additional equipment
Fusion Splicer
• Splicing is the process of connecting two
bare fibres directly without any connectors.
• Splicing provide much lower insertion loss
compared to fibre connectors that’s why Inserting a fibre in the
Splicing Machine
Splicing is preferred over the use of Splicer after cutting
Connectors.
• It is the process of fusing or welding two
fibres together usually by an electric arc.
• It provides for the lowest loss and least
reflectance
• It also provides the strongest and most
reliable joint between two fibres.
Alignment Check by the After the approval of the
Machine Alignment the fusion starts
Digital Multiplexing Hierarchies
Two types of hierarchies SDH and PDH.
PDH
• Greek word ‘Plesio’ means Close so PDH the different stages of mux are almost
synchronous but not completely synchronous
• the PDH is a technology for transporting voice or data between multiple devices and
which are working with clock sources with accepted tolerance levels for
synchronisation
• PDH used in 2Mb,8Mb,34Mb and 140 Mb systems only.
SDH
• All SDH equipment is based on the use of a single master reference clock source &
hence SDH is synchronous
• Compatible with the majority of existing PDH bit rates
• SDH provides for extraction/insertion, of a lower order bit rate from a higher order
aggregate stream, without the need to de-multiplex in stages
Components of SDH hierarchy
STM • PDMUX
• It is an electrical device which converts • I t is an electronics device which can
optical energy to electrical energy. It convert 2 mbps signal of each E1 into
consists of 63 E1s. 32 time slots with each subscriber end
such as telephone, computer
• STM1 COMPONENTS exchange, etc.
▫ Synchronous card • PDMUX components
▫ Text card ▫ PSU card
▫ ADM card ▫ NIM card
▫ PSU card ▫ TRIB card
▫ OLI(optical line interconnect) card • Among 32 time slots 30 slots are
▫ Ethernet card usable since time slot 0 and 16 are
• Various connectors pig tail, patch cord used for synchronisation and signalling
etc. respectively.
Components of SDH hierarchy
SDH Multiplexers used in RAILTEL
NMS(Network Management System)
• NMS used in Indian railways Superset Management System 4.0
• It is a window based operating system to control FLEXIMUX equipment.
• It comprises information from all FLEXIMUX equipment connected in
network
• Real time monitoring of network
• Execution of various diagnostics &telecommunication.
Interface and commands
This Menu Bar consists the following
Menu options:
CREATING A NETWORK File Draw Drag Site List Equipment State
Click Setup->Network-> Edit Network ...then
enter your password
The Network Configuration screen appears
Now Click -> File -> Open
Drawing
Board
i If no site is created yet, you will receive message
'Create Site First'. Otherwise, network diagram will
be loaded
Interface and commands
NETWORK DIAGRAM
LIST OF CONTROL COMMANDS
FLEXIMUX
• Auto
• Bypass
• Digital Bypass
• Tribal loop back
• Channel loopback
/•
• Mw Signal
• Tributary B remote loopback
• Activate
• DeactivateG821 Reset
A Typical Network
Diagram
Power supply of OFC system
• Power supply consists of secondary cells.
• Secondary cell is used only due to its discharging purposes DC- 48 V which is absent
in primary cells.
• Lead Secondary cells (Pb,PbO2 as electrodes and dil. H2SO4 as electrolyte used for
both charging and discharging
• Battery charger (50 A,48 v) for charging of cells
▫ SMPS charging
▫ 50 A,48 v Manual charger
Power supply of OFC system
• Modes of charging of battery cells:-
• Initial charging.
▫ Full charge then full discharge.
• Automatic Floating Mode.
▫ Discharge while the equipment is compensated and charging using charger.
• Boost mode.
▫ charging at high rate.
• Trickle Mode charging.
Thank You
