3GPP42.068Release 16Stage 1TSVoice Group Call Service (VGCS)
If a service subscriber wants to establish a voice group call while not subscribed to the service or the network cannot provide the service for some reason, an indication will be provided to the calling service subscriber to notify him of the reason of failure.
If a dispatcher wants to establish a voice group call while not entitled to do it or the network cannot provide the service for some reason, the call shall be rejected. The network shall give an appropriate indication to calling dispatchers who are GSM subscribers.
A voice group call will be considered established as soon as the originating cell in case of a service subscriber originated voice group call or any one cell within the group call area in case of a dispatcher originated voice group call has been included . If this cannot be achieved within a specified time the call will be released.
If a cell is excluded from the group call area because of pre-emption, the voice group call shall be maintained.