ITU-T Recommendations

This new Recommendation describes the procedures and the signalling protocol for the Call Completion supplementary services in ITU-T H.323.The Call Completion supplementary services are Completion of Calls to Busy Subscribers (SS-CCBS) and Completion of Calls on No Reply (SS-CCNR).SS-CCBS enables a calling User A, encountering a busy destination User B, to have the call completed when User B becomes not busy, without having to make a new call attempt.SS-CCNR enables a calling User A, encountering a destination User B that, though alerted, does not answer, to have the call completed when User B becomes not busy again after a period of activity, without having to make a new call attempt.This Recommendation makes use of the "Generic functional protocol for the support of supplementary services in H.323" as defined in ITU-T H.450.1.This Recommendation requires H.323 version 2 (1998) or later. Version 2 products can be identified by H.225.0 messages containing a protocolIdentifier? {itu-t (0) recommendation (0) h (8) 2250 version (0) 2} and H.245 messages containing a protocolIdentifier ? {itu-t (0) recommendation (0) h (8) 245 version (0) x} where "x" is 3 or higher.The procedures and the signalling protocol of this Recommendation are derived from the Call Completion supplementary service specified in ISO/IEC 13866 and ISO/IEC 13870.