scope:

This standard specifies the stage three of the pan-European Integrated Services Digital Network (ISDN) as provided by European public telecommunications operators for the Subaddressing (SUB) supplementary service at the T reference point or coincident $ and T reference point (as defined in CCITT Recommendation 1.411 LII) by means of the Digital Subscriber Signalling one (DSS1). Stage 3 identifies the protocol procedures and switching functions needed to support a telecommunications service (see CCITT Recommendation 1.130 [2]).

In addition this standard specifies the protocol requirements at the T reference point where the service is provided to the user via a private ISDN.

This standard does not specify the additional protocol requirements where the service is provided to the user via a telecommunications network that Is not an ISDN.

The SUB supplementary service allows the called (served) user to expand his addressing capacity beyond the one given by the ISDN number.

The SUB supplementary service is applicable to all telecommunication services.

Further parts of this standard shall specify the method of testing required to identify conformance to this standard.

This standard is applicable to equipment supporting the SUB supplementary service, to be attached at either side of a T reference point or coincident S and T reference points when used as an access to the public ISDN.