What are the telecommunications systems that IR uses?

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What are the telecommunications systems that IR uses?

July 17, 2019, 2:23 PM

Most of IR’s telecommunications needs are handled by telephone / telegraph cables and other control communication cables running alongside the tracks (often underground in electrified areas) or overhead (usually in non-electrified areas). Important circuits of control and communication include section control for overall control of train running, deputy control and FOIS (Freight Operations Information Systems) for freight movement monitoring, traction power control, remote control, and SCADA sysems for control and switching of the OHE in electrified sections, traction loco control for coordinating locmotive allocations, engineering control for coordinating maintenance and permanent-way work, and S&T control for signalling and related communications. More recently, computerized ticketing/booking and other status information as well as more monitoring and data processing and management systems have come on line and have resulted in new communication systems carrying their data traffic as well.

Low-traffic and rural areas often have fairly simple communications set-ups. Token instruments in many cases are connected by fairly simple telegraph mechanisms. Station masters and signal cabins usually have telephonic contact with their counterparts up and down the track. IR’s telephony is a mixture of Strowger (mechanical relay) exchanges and more modern digital exchanges, with the older electromechanical systems being gradually phased out.

In electrified areas, telephone and other communications are usually carried on shielded underground cables to avoid interference from the OHE. Often 4-wire circuitry is used (2 wires for transmission and 2 for reception) to minimize interference problems. Repeaters are used every 40-50km for loaded/balanced cables; amplifiers / equalizers are used at stations for non-balanced cables. In some areas, old analog twisted pair wires between stations have been utilized in a more efficient manner to carry 6 or so digitized voice channels (ADPCM), for distances up to about 10km. (The system is known as TeNET, and was developed by IIT Madras.)

For longer distances (coordinating across longer stretches, zonal communications, administration) IR uses microwave communications (2GHz and 7GHz (7.125GHz and 7.425GHz) for administration, 8GHz and 18GHz for control communications) with backup wireline telephony. Analog microwave equipment is from Harris and Toshiba. The microwave links besides having more bandwidth than the older telephony cables also avoid the problem of cable theft. Most links have 120 channels, and more recent ones (post-1987) have 960 channels.

The four major metropolises are interconnected by a digital 34+2 Mbps microwave channel [1/00] with equipment from Alcatel and NEC. In 1999, IR had nearly 15,000 route-km of analog microwave links and 3,700 route-km of digital microwave links. The UHF microwave links use 5 to 7 repeaters for each division, spaced every 50-60km. Each repeater station has two transmitters, two receivers, standby battery and generator sets, etc. Some of these handle both analog and digital links (100+ analog channels, 56 digital channels in a common configuration). Data loggers report status back to the divisional headquarters.

In addition, spread-spectrum CDMA communication is in use between a few stations ([1/00] Mumbai-Mathura on WR, Mumbai-Wadi on CR, Wadi-Secunderabad on SCR). Other major routes not covered by these have UHF TDMA links. Satellite ‘micro-earth terminals’ are used at several remote locations (as of 2000, over 120 such).

Major stations’ computer networks are also connected via trackside cables. Control communications and control for electric traction substations is usually done through trackside metal cabling; some stretches have now been upgraded to use optical fibres. Signalling systems of some nearby stations in busy areas are interconnected with fibre-optic rings that also carry phone and data traffic in addition to signalling and control traffic.

Much of the PRS system for ticketing and reservations (see below) is connected together by 64kbps leased lines, although lines of higher bandwidth are beginning to be used as more applications are being made available (train status enquiry systems, station enquiries, etc.).

With the spread of the Internet in India, many of the railway institutions are now connected to the public Internet, and they are also connected among themselves with a wide-area intranet known as ‘RAILNET’ which covers most of the zonal and divisional headquarters, training institutes, production units, and offices of the Ministry of Railways.

Optical Fibre Communication

Since about 2000, a major effort has been underway to provide optical fibre communication links between stations. Part of the push for this came from the Department of Telecommunications’ declining interest in maintaining IR’s leased-line communication and control circuits since its (DOT’s) own infrastructure was increasingly moving to microwave and optic fibre links.

However, the other reason is the promise of raising revenue by commercial marketing of the communication capacity to Internet and telecom companies and others. So far [2/02], fibre-optic links have been provided along the routes among New Delhi, Ahmedabad, Mumbai, Pune, Bangalore, Chennai, Hyderabad, and Kolkata. A 24-fibre cable standard is followed.

Source – IFRCA.org

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