Data Links
Communication between interlockings and TFMs is by electronic data packages termed 'telegrams'. Telegrams are transmitted via 'data links', comprising twisted pair copper cable. The data links are duplicated for availability.
A 'data link module' (DLM) is the interface between the data link and the TFMs. A DLM has a blue label.
For transmission over longer distances, fibre-optic cable and pulse-code modulation may be used. Another type of module, the 'long distance terminal' (LDT) is available for this purpose. An LDT has a gold coloured label.
Read more about this topic: Solid State Interlocking
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