scope:

This standard specifies the stage three of the Call Hold supplementary (HOLD) supplementary service for the pan-European Integrated Services Digital Network (ISDN) as provided by European public telecommunications operators at the T reference point or coincident S and T reference point (as defined in CCITT Recommendation I.411 [1]) by means of the Digital Subscriber Signalling System No. one (DSS1) protocol. Stage three identifies the protocol procedures and switching functions needed to support a telecommunications service (see CCITT Recommendation I.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 HOLD supplementary service allows a user to interrupt communications on an existing call and then subsequently, if desired, re-establish communications.

The HOLD supplementary service is applicable to all circuit-switched telecommunication services.

Further part(s) of this standard specify the method of testing required to identify conformance to this standard.

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