Along with performing all the functions of Mode A and C transponders, Mode S transponders also have a data link capability. Upon interrogation, Mode S transponders transmit information about the aircraft to the secondary surveillance radar network, the TCAS receivers on board other aircraft, and the ADS-B network. This information includes the call sign of the aircraft, its position, altitude heading and the aircraft’s permanent ICAO 24-bit address. Mode S transponders provide greater position accuracy than Modes A and C and are backward compatible, which means that an aircraft equipped with a Mode S transponder can still be used to send replies to Mode A or C interrogations.