11.5A Functional requirement of group call serving MSC (within a RANflex pool)

3GPP43.069Release 16Stage 2TSVoice Broadcast Service (VBS)

The process in the group call serving MSC is shown in figure 7A.

The group call serving MSC is either the anchor MSC or a relay MSC.

Successful call set-up initiated by a service subscriber

When receiving a SEND_GROUP_CALL_INFO interrogation request from a VMSC, the group call serving MSC (in a RANflex configuration with group call redundancy: the selected group call serving MSC) interrogates its associated GCR to retrieve the Broadcast Call Reference and the Anchor MSC address from the given cell Id / Group Id pair and return this information to the VMSC. The group call serving MSC shall temporarily store in its associated GCR the initiating subscriber’s IMSI and originating cell Id as received in the interrogation request from the VMSC. The group call serving MSC shall then wait for the broadcast call being set up:
If the group call serving MSC is the anchor MSC, it waits for an IAM from the VMSC; if the group call serving MSC is a relay MSC, it waits for a PREPARE_GROUP_CALL from the anchor MSC.
Waiting for the broadcast call being set up shall be supervised by a timer T3.
When receiving IAM from the visited MSC, timer T3 is stopped and processing continues in the process VBS_Handling_Anchor_MSC after reception of the VBS call setup request in Idle state.
When receiving PREPARE_GROUP_CALL from the anchor MSC, timer T3 is stopped and processing continues in the process VBS_Handling_Relay_MSC after reception of PREPARE GROUP CALL in Idle state.

Unsuccessful call set-up

In a RANflex configuration: If the broadcast call reference could not be retrieved or the GCR returns a negative response indicating "on-going call" to the group call serving MSC, an error indication is returned to the VMSC and the process returns to the idle state.

In a RANflex configuration with group call redundancy: If the GCR returns a negative response indicating "on-going call" to the group call serving MSC, the group call serving MSC forwards the SEND_GROUP_CALL_INFO message within the same redundancy pool to the group call serving MSC where the broadcast call is ongoing.

If the selected group call serving MSC recognizes that the group call serving MSC where the broadcast call is ongoing is out of service or if that group call serving MSC responds with a positive SEND_GROUP_CALL_INFO response (i.e. the GCRs are out of synch and the broadcast call at the other group call serving MSC is not ongoing), then the selected group call serving MSC repeats the GCR interrogation including "ongoing call override indication". If the group call serving MSC where the broadcast call is ongoing responds with a negative SEND_GROUP_CALL_INFO response (ongoing call), then the selected group call serving MSC returns a negative SEND_GROUP_CALL_INFO response indicating "ongoingGroupCall" to the VMSC in order to force the mobile station of the service subscriber to look for notifications of the respective group ID on the NCH and join the broadcast call.

At timeout of timer T3 the temporarily stored initiating subscriber’s IMSI and originating cell Id shall be deleted from the GCR.

Figure 7A: The VBS handling process in the group call serving MSC (sheet 1 of 2)

Figure 7A: The VBS handling process in the group call serving MSC (sheet 2 of 2)