03.693GPPStage 2TSVoice Broadcast Service (VBS)
The VBS handling process in the anchor MSC is shown in figure 5
Successful call set-up
When the VBS handling process in the anchor MSC receives a VBS call set-up request from either a dispatcher or a service subscriber currently located in the anchor MSC’s area or a service subscriber currently located in a relay MSC’s area, it interrogates its associated GCR to retrieve the broadcast call attributes, and waits for a response.
If the GCR returns a positive response containing the broadcast call attributes, the anchor MSC sets up the downlinks to the cells inside the MSC area of the group call anchor MSC into which the call is to be sent, sets up the connections to the dispatchers to which a dedicated link is to be established , sets up the connections to the relay MSCs into which the call is to be sent and waits for call release.
Procedure Setup Connections to Relay MSCs
The procedure is shown in figure 6.
The procedure sends PREPARE_GROUP_CALL messages to all relay MSCs and waits for the responses.
If a positive response containing an Group Call number is received from a relay MSC, the anchor MSC constructs an IAM using the Group Call number as called party address, sends it to the relay MSC and waits for the SEND_GROUP_CALL_END_SIGNAL message.
If the SEND_GROUP_CALL_END_SIGNAL message is received, the procedure returns an acknowledgement to the relay MSC and checks whether responses from other relay MSCs are outstanding. Relay MSCs that do not send positive responses on the PREPARE_GROUP_CALL message are no longer considered to belong to the list of relay MSCs for this VBS call.
Negative response received from the GCR
If the GCR returns a negative response to the anchor MSC indicating that the call is already on-going, the anchor MSC checks whether the call was initiated by a dispatcher. If so, the dispatcher is connected to the on-going call and the process returns to the idle state. If the call was initiated by a service subscriber, a Release message indicating ‘user busy’ is returned 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.
If the negative response from the GCR indicates any other reason than ‘on-going call’ the VBS call set-up request is rejected by sending a release message back to the initiator and the process returns to the idle state.
When receiving a release message either from a dispatcher who is allowed to terminate the voice broadcast call or from the service subscriber who has initiated the VBS call in the anchor MSC area or in a relay MSC area, the connections to the relay MSCs are released, all connections to dispatchers are released, all downlinks to cells inside the anchor MSC area are released, the GCR is informed that the call is no longer on-going and the process returns to the idle state.
Figure 5: VBS handling process in the anchor MSC (sheet 1 of 2)
Figure 5: VBS handling process in the anchor MSC (sheet 2 of 2)
Figure 6: Set-up connection to relay MSCs (sheet 1 of 1)