A thin route optical fibre communication system for railway traffic control

Railway traffic control requires dedicated point-to-point and point-to-multipoint circuits for communication over larger number of signal points spread along the track. A typical despatcher control section spreads over 200 kms with 30 to 40 signal points. Until the mid 1980s, such communication were economically provided by copper quad cable in electrified territory. Development in optical fibre technology has changed the scenario and fibre finds increasing use in railway telecommunication networks due to its distinctive advantages. However some of the railways requirements are too specialized. These include omnibus circuits with large number of tappings, closely spaced repeaters, lineside emergency communication requirement, transmission of safety information and the ability to provide on demand service. The technology of optical fibre therefore requires adoptions to meet these specialized requirements. In this paper, the authors describe an optical fibre based railway communication system used by Indian Railways and conclude that even though large number of repeaters are used in the link, the performance quality is satisfactory and optical fibre based communications are economical in the railway environment. Reliability of the link can be improved through additional fibres or through alternate media. A hybrid solution based on optical fibre and copper cable is proposed to achieve economy without sacrificing quality and reliability.