UIC 568

Examples of those commands and data is loudspeaker messages, train destination signs, and control of doors (locked/un-locked, open/close) and others.

Very early in the development of the standard, it was decided that two conductors and pins should be reserved for remote operation of the locomotive (when using control cars).

The remaining five wires are used for the Train Communication Network (TCN)-bus and side-sensitive door control.

This cable carries single-phase electric power at 1500 volts AC, 50 Hz (with the tracks as the ground connection), supplied from the locomotive, or in some cases a carriage with a generator.

In order to use this power, each carriage is equipped with a transformer, which reduces the voltage and supplies a number of electric groups (typically one for heating/air-conditioning, one for lighting, one for outlets to passengers and so on).