scope:

This first part of EN 300 359 specifies the stage three of the Completion of Calls to Busy Subscriber (CCBS) 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 ITU-T Recommendation I.411 [6]) 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 telecommunication service (see CCITT Recommendation I.130 [3]). In addition, the present document specifies the protocol requirements at the T reference point where the service is provided to the user via an intermediate private ISDN. The present document does not specify the additional protocol requirements where the service is provided to the user via a telecommunications network that is not an ISDN.