Summary

This Recommendation specifies the stage three of the Completion of Calls to Busy Subscribers (CCBS) supplementary service for the Integrated Services Digital Network (ISDN) at the T reference point or coincident S and T reference point by means of the Digital Subscriber Signalling System No. 1 (DSS 1) protocol. Stage three identifies the protocol procedures and switching functions needed to support a telecommunication service.

The CCBS supplementary service enables a calling user A, encountering a busy destination B, to be notified when the busy destination B becomes not-busy and to have the service provider reinitiate the call to the specified destination B, if user A desires.

The CCBS supplementary service is applicable to all circuit-switched basic telecommunication services using one B-channel.