The present document defines the signalling and media interface between the Network Switching Subsystem and the Fixed Terminal Subsystem in order to provide a clear set of services needed for GSM-R operations. This includes voice call service and available call-related supplementary services. In addition, requirements for specific implementation of the signalling and media interface within either the Network Switching Subsystem or the Fixed Terminal Subsystem are stated where applicable. The present document addresses the Internet Layer and upwards of the Internet Protocol Suite IETF RFC 1122 [i.18] on the signalling and media interface.

Any service other than voice call service and call-related supplementary services (such as data services, Short Message Service, etc.) is out of scope of the present document; additional features may be addressed in future releases.

The present document does not specify any other interface between the Network Switching Subsystem and the Fixed Terminal Subsystem nor does it cover any internal interfaces of either NSS or FTS. Such interfaces may be addressed in a future release of the present document.

The present document does not address any specific 3GPP Release or Architecture.