11.5 Functional requirement of Relay-MSC

03.693GPPStage 2TSVoice Broadcast Service (VBS)

The VBS handling process in the relay MSC is shown in figure 7

Successful call set-up initiated by a service subscriber

When the VBS handling process in the relay MSC receives a VBS call set-up request from a service subscriber currently located in a relay MSC’s area, it interrogates its associated GCR to retrieve the anchor MSC address and waits for a response.

If the GCR returns a positive response containing the anchor MSC address, the relay MSC sets up a dedicated connection for the initiating service subscriber to the anchor MSC by constructing an IAM with CLI set to the NDC plus prefix for VBS plus broadcast call reference, sending it to the anchor MSC, and waits for call release.

Negative response received from the GCR

If the GCR returns a negative response to the relay MSC indicating that the call is already on-going, the relay 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 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.

Successful call set-up initiated by the anchor MSC

When the VBS handling process in the relay MSC receives a PREPARE_GROUP_CALL message from the anchor MSC, it interrogates its associated GCR to retrieve the list of cells inside the relay MSC area into which the call is to be sent.

If the GCR returns a positive response, the relay MSC requests an Group Call number from its VLR.

If the VLR returns a Group Call number, a PREPARE_GROUP_CALL acknowledgement containing the Group Call number is returned to the anchor MSC and the relay MSC waits for the incoming call.

If the incoming call identified by the Group Call number is received, the relay MSC releases the Group Call number, sets up the downlinks to the cells inside the relay MSC area into which the call is to be sent, sends a SEND_GROUP_CALL_END_SIGNAL message to the anchor MSC and waits for the call to be released.

Negative response received from the GCR

If the GCR returns a negative response to the relay MSC, the relay MSC returns a PREPARE_GROUP_CALL negative response to the anchor MSC and returns to the idle state.

No Group Call number received from VLR

If the VLR could not allocate an Group Call number, the relay MSC returns a PREPARE_GROUP_CALL negative response to the anchor MSC, informs the GCR that the call is no longer on-going and returns to the idle state.

Call release

When receiving a release message from the anchor MSC for the dedicated connection which was set-up to for the initiating service subscriber located in the relay MSC area, the relay MSC releases the connection to the service subscriber and the process returns to the idle state.

When the initiating service subscriber releases the call, the relay MSC sends a release message for the dedicated connection to the anchor MSC and the process returns to the idle state.

When receiving a release message from the anchor MSC for the connection which was set up using the Group Call number, the relay MSC releases all downlinks to cells inside the relay MSC area, informs the GCR that the call is no longer on-going and the process returns to the idle state.

Figure 7: VBS handling process in the relay MSC (sheet 1 of 3)

Figure 7: VBS handling process in the relay MSC (sheet 2 of 3)

Figure 7: VBS handling process in the relay MSC (sheet 3 of 3)