11.5B Functional requirement of VMSC (within a RANflex pool)

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

The process in the visited MSC is shown in figure 7B.

Successful call set-up initiated by a service subscriber

When the VBS handling process in the originating MSC receives a VBS call set-up request from a service subscriber, the VMSC derives the address of the group call serving MSC or group call serving MSC redundancy pool from the requesting subscriber’s current LAC. If the VMSC is the group call serving MSC or belongs to the group call serving MSC redundancy pool of the requesting subscriber’s current LAC, processing continues in the process VBS_Handling_Anchor_MSC or VGCS_Handling_Relay_MSC after reception of the VGCS call setup request in Idle state. Otherwise, the visited MSC interrogates the group call serving MSC by means of the MAP service SEND_GROUP_CALL_INFO to retrieve the anchor MSC address and Broadcast Call Reference and waits for a response.

If the group call serving MSC returns a positive response containing the address of the anchor MSC or anchor MSC redundancy pool and the address is different from the visited MSC’s address, the originating MSC sets up a dedicated connection for the initiating service subscriber to the anchor MSC by constructing an IAM with calling party number set to VBS prefix plus broadcast call reference, and with a generic number parameter with the number qualifier indicator set to "additional calling party number" and address signal set to the address of the group call serving MSC (in a RANflex configuration with group call redundancy this shall be the same address as used to route the SEND_GROUP_CALL_INFO message , i.e. identifying the redundancy pool), sending it to the anchor MSC, and waits for call release. If the VMSC is the anchor MSC or belongs to the anchor MSC redundancy pool, processing continues in the process VBS_Handling_Anchor_MSC after reception of the VBS call setup request in Idle state.

Negative response received from the group call serving MSC

If the group call serving MSC returns a negative response to the originating MSC indicating that the call is already on-going, the originating MSC sends a Release message indicating "user busy" to the service subscriber 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 group call.

If the negative response from the group call serving MSC indicates any other reason than "on-going call" the VBSS call set-up request is rejected by sending a release message back to the initiator and the process returns to the idle state.

Figure 7B: The VBS handling process in the VMSC