11.7 Functional requirement of VLR
3GPP43.068Release 17Stage 2TSVoice Group Call Service (VGCS)
The Group Call number allocation process in the VLR is shown in figure 12.
Successful procedure
When receiving a request from the relay MSC to allocate a Group Call number, the VLR checks if a Group Call number is available. If so it selects a Group Call number, marks the number as allocated, returns a positive response including the Group Call number to the MSC, starts a supervision timer and waits for removal of the Group Call number. If the VLR receives a request to release the Group Call number, the VLR marks the Group Call number as free and the process returns to the idle state.
No Group Call number available
If no Group Call number is available, the VLR returns a negative response indicating "no Group Call number available" to the MSC and the process returns to the idle state.
Supervision timer expires
If the supervision timer expires, the VLR indicates to the relay MSC that the dialogue has to be aborted.
Figure 12: The Group Call number allocation process in the VLR
11.8 Functional requirement of SMS Gateway MSC
SM MT delivery
When receiving a short message TPDU from the SC, the SMS‑GMSC shall inspect the parameters and identify the group call reference.
NOTE: The SMS‑GMSC may be identical to the MSC.
If the parameters are incorrect then the SMS-GMSC shall return the appropriate error information to the SC in a failure report (see clauses 9 and 10 of 3GPP TS23.040 [14]).
If no errors are found within the parameters the SMS-GMSC shall send the MT_ForwardSM_For_VGCS_REQ message to transfer the received short message to the anchor MSC or anchor MSC redundancy pool using the routing information derived from the group call reference.
If the SMS-GMSC receives the MT_ForwardSM_For_VGCS_RES message indicating the voice group call is established and including a list of identities of dispatchers, it may optionally initiate point-to-point short message transfer attempts to the dispatchers who are connected to the voice group call.
If the SMS-GMSC receives the MT_ForwardSM_For_VGCS_RES message indicating the voice group call is not established, it shall either
i) discard the short message and return the appropriate error information to the SC, or
ii) initiate point to point short message transfer attempts to the members of the group.
NOTE: How the routing information of the voice group call subscribers for the point to point SMS transfer can be derived from the group call reference is out of scope of this specification and implementation dependent. This can be achieved e.g. by an internal or external database.
Figure 13: The process in the SMS-GMSC (sheet 1 of 1)