ETSI TS 124 642 specifies the stage three Protocol Description of the Completion of Communications to Busy Subscriber (CCBS) service, the Completion of Communications on no Reply (CCNR) service, and Completion of Communications on not Logged-in (CCNL) service, based on stage one and two of the ISDN supplementary services. It provides the protocol details in the IP Multimedia (IM) Core Network (CN) subsystem based on the Session Initiation Protocol (SIP) and the Session Description Protocol (SDP).

The Completion of Communications to Busy Subscriber CCBS service enables user A, encountering a busy destination B, to have the communication completed without having to make a new communication attempt when the destination B becomes not busy.

The Completion of Communications on No Reply CCNR supplementary service enables user A, encountering a destination B which does not answer the communication (No Reply), to have the communication completed without having to make a new communication attempt when the destination becomes not busy after having initiated an activity.

The Completion of Communications on Not Logged-in CCNL supplementary service enables user A, encountering a destination B which is not registered with the IMS network, to have the communication completed without having to make a new communication attempt when the destination becomes registered.

The present document is applicable to User Equipment (UE) and Application Servers (AS) which are intended to support the CCBS and CCNR supplementary services.