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 Call Waiting (CW) supplementary service 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 Signaling one (DSS1). Stage 3 identifies the protocol procedures and switching functions needed to support a telecommunications services (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 CW supplementary service permits a subscriber to be notified of an incoming call (as per basic all procedures) with an indication that no interface information channel is available. The user has then the choice of accepting, rejecting or ignoring the waiting call (as per basic call procedures).

The CW supplementary service is considered meaningful when applied to the telephony teleservice and the speech and 3,1 kHz audio bearer services. Furthermore, it may also be meaningful when applied to other services.

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

This standard is applicable to equipment supporting the CW 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.