Presented bySreerup Chowdhury

Railway OFC training

•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.

Introduction

•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.

Training Topics

• 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.

Advantages of using optical fibre

• An Optical Fibre is a long, thin strand made with pure glass about the diameter of a human hair.

• OFC consists of Core, Cladding, Buffers and Jacket as shown in figure.

Optical FibreTypes of optical fibres.

• Single-mode step index• Multi-mode step index• Multimode graded index

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 Splicing is preferred over the use of 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.

Additional equipment

Splicing Machine Inserting a fibre in the Splicer after cutting

Alignment Check by the Machine

After the approval of the Alignment the fusion starts

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

Digital Multiplexing Hierarchies

STM• It is an electrical device which converts

optical energy to electrical energy. It consists of 63 E1s.

• STM1 COMPONENTS▫ Synchronous card▫ Text card▫ ADM card▫ PSU card ▫ OLI(optical line interconnect) card▫ Ethernet card

• Various connectors pig tail, patch cord etc.

Components of SDH hierarchy• PDMUX• I t is an electronics device which can

convert 2 mbps signal of each E1 into 32 time slots with each subscriber end such as telephone, computer exchange, etc.

• PDMUX components ▫ PSU card▫ NIM card▫ TRIB card

• Among 32 time slots 30 slots are usable since time slot 0 and 16 are used for synchronisation and signalling respectively.

Components of SDH hierarchy

SDH Multiplexers used in RAILTEL

•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.

NMS(Network Management System)

Interface and commands

CREATING A NETWORKClick Setup->Network-> Edit Network ...then enter your password

The Network Configuration screen appears

DrawingBoard i

This Menu Bar consists the following Menu options:File Draw Drag Site List Equipment State

Now Click -> File -> Open

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 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.

Power supply of OFC system

Thank You