13.13 Completion of Calls to Busy Subscriber (CCBS)

23.2053GPPBearer-independent circuit-switched core networkRelease 17Stage 2TS

The procedures specified in 3GPP TS 23.093 [16] for the Completion of Calls to Busy Subscriber supplementary service and 3GPP TS 23.108 [18] shall be followed. The following clauses describe the additional requirements for the bearer independent CS core network.

13.13.1 Clearing when tones/announcements are provided to the calling subscriber

If an announcement is to be provided for the purpose of notifying the subscriber that CCBS activation is possible, the MSC server shall select an MGW. The MGW performs the traffic channel assignment if the bearer termination has not been through-connected (as described in clause 6.1 for the basic mobile originating call). The MGW through-connects the bearer before providing the in-band information. The MSC server requests the MGW to play an announcement/tone using the Play Announcement or Send Tone procedure. When the announcement has completed the MGW notifies the MSC server (using the Announcement Completed procedure as described in clause 14.6) that the announcement is complete.

Otherwise the MSC server handles the call clearing as described in clause 7.

13.13.2 Network initiated mobile originated call

The call is established as described in clause 6.1 for basic mobile originating call. Early Traffic Channel Assignment

Within CCBS there is an option for a CCBS call to establish a bearer before setup in state "CC-establishment confirmed". In this case the MSC server shall check whether an access bearer assignment modification has to be performed after receiving the setup message from UE. Example

For the network model, please refer to figure 6.1.

Figure 13.26 shows the message sequence chart for the network initiated mobile originating call using the option assignment after A and B party alerting. In the following, the case with backward bearer establishment is considered.

Figure 13.26: Network initiated mobile originating call establishment with assignment
after A and B party alerting (message sequence chart)

13.13.3 CCBS Information conveyed by Call Signalling

For CCBS, application specific information needs to be conveyed via the call signalling. Specific details of the CCBS information are described in 3GPP TS 23.093 [16].