The group-broadcast group is defined as a set of groups, not a set of MCPTT users. The group-broadcast group is also defined with a hierarchy. It is expected that the MCPTT user that originates the group-broadcast group call is the only one transmitting media during the group-broadcast group call and that the group-broadcast group call is terminated when the transmission is complete. However, if the override feature is enabled, then the call originator may be overridden.
illustrates the procedure for group-broadcast group call establishment.
The group (e.g. A) to which MCPTT client 1 and MCPTT client 2 are members is a subordinate group of the group-broadcast group (i.e., the group-broadcast group was defined with group A as a subordinate group).
The group (e.g. A) currently has an on-going MCPTT group call that is not an MCPTT emergency group call.
The call initiator of the group-broadcast group is a member of another group (e.g., X, not group A) which is also a subordinate group of the group-broadcast group (i.e., the group-broadcast group was defined with group X as a subordinate group).
The group-broadcast group and its subordinated groups are defined in the same group management server and served by the same MCPTT server.
Optionally, MCPTT client 3 may have an activated functional alias for the group communication.
The MCPTT server may have subscribed to the MCPTT functional alias controlling server within the MC system for functional alias activation/de-activation updates.
MCPTT user at MCPTT client 3 initiates the group-broadcast group call setup procedure.
The MCPTT client 3 sends a group-broadcast group call request to the MCPTT server. The MCPTT user at MCPTT client 1 may include a functional alias used for the broadcast group call.
The MCPTT server checks whether the provided functional alias can be used and has been activated for the MCPTT user. The MCPTT server needs to resolve the group-broadcast group ID into its subordinate groups in order to contact the affiliated MCPTT users of those subordinate groups.
The MCPTT server then needs to consider any on-going group calls on those subordinate groups because this may affect the behaviour for what happens next. In this case a group call exists on a subordinate group. Thus, the MCPTT users involved in the group call on this subordinate group.
Optionally the on-going group call on a subordinate group may be terminated in which case the MCPTT client 1 and MCPTT client 2 need to be sent a Group call release request.
The MCPTT client 1 and MCPTT client 2 then notify their users of the group call release request.
The MCPTT client 1 and MCPTT client 2 respond to the group call release request by sending a group call release response.
A group-broadcast group call request is sent to both the MCPTT client 1 and the MCPTT client 2. The request may contain the functional alias of the calling party.
MCPTT client 1 and MCPTT client 2 notify their users of the incoming group-broadcast group call. The functional alias of the calling party, if available, is presented to the users.
MCPTT client 1 and MCPTT client 2 respond to the group-broadcast group call request by sending a group-broadcast group call response.
The MCPTT server responds to MCPTT client 3 (the call initiator) that the group-broadcast group call has been established by sending a group-broadcast group call response.
The MCPTT client 3 notifies its user that the user can begin transmitting using the group-broadcast group call resources.
Resources are now available for the transmission from MCPTT client 3
to MCPTT client 1
and MCPTT client 2
. Once the user of MCPTT cleint 3 completes transmitting, the group-broadcast group call is releases as are the resources.