Telecommunications are an essential part of the railway system. A centralised control system means that a vast amount of information has to be transmitted reliably, sometimes over very long distances. To maintain system availability in the event of a cable failure, the fibre-optic track cables are being laid on either side of the line, alongside the permanent way, to create redundancy. Copper cables are only being laid on one side. One advantage of fibre-optic cables is their higher transmission speed compared to copper. Another is the fact that all the connections made using a fibre-optic cable are monitored. Fibre-optic cables also have advantages in terms of electro-magnetic compatibility (EMC). If a fibre-optic cable failure is detected, its circuits can be rerouted.
In general, telecommunications systems, whether hard wired or wireless, link all the external installations together and with the signalling centre. The external installations include the electronic signalling centres, GSM-R base stations, sectioning points and passenger information systems on platforms. The substations and their fire and intruder alarm systems are fitted with a communications link which allows their condition to be monitored at any time. This can be achieved by integrating the external systems into the dedicated railway alarm system.