Content for  TS 23.379  Word version:  19.4.0

User at MCPTT client 1 would like to initiate an MCPTT group call with a selected group (identified by MCPTT group ID). The MC service user may select a functional alias.

MCPTT client 1 sends a group call request towards the MCPTT server via the SIP core, which hosts the group selected by the user and identified by MCPTT group ID. The group call request also contains the MCPTT group ID and an SDP offer containing the MCPTT client media parameters. If there is a floor request to transmit, then the group call request contains an indication of an implicit floor request. If the MC service user of MCPTT client 1 has selected a functional alias, then the group call request contains that functional alias. If the group call request contains an implicit floor request it may also include location information.

The MCPTT server checks whether the user of MCPTT client 1 is authorized to initiate a group call for the selected group. If authorized and the group call is ongoing for that MCPTT group ID, the MCPTT server adds the requesting MCPTT client 1 to the existing MCPTT group call and notifies the MCPTT client 1 that the MCPTT group call is already in progress. Otherwise, MCPTT server resolves the MCPTT group ID to determine the members of that group and their affiliation status, based on the information from the group management server. The MCPTT server evaluates the applicable group call start criteria defined for this group (e.g. minimum number of affiliated members, specific members affiliated) and determines whether the group call setup can proceed. If the functional alias is provided only in the group call request, or via binding, the MCPTT server proceeds with the value that is provided. If the functional alias is provided in both the group call request and via binding, it is up to the MCPTT server implementation to determine a value for the functional alias to be used. If present, the MCPTT server checks whether the provided functional alias is allowed to be used and has been activated for the user. If location information was included in the group call request, the MCPTT server checks the privacy policy of the MCPTT user to decide if the location information of MCPTT client 1 can be provided to other users on the call (refer to Annex A.3 "Authorisation to provide location information to other MCPTT users on a call when talking").

MCPTT server includes information that it communicates using MCPTT service, offers the same media parameters or a subset of the media parameters contained in the initial received request and sends the corresponding group call request via the SIP core towards the MCPTT clients of each of those affiliated group members. MCPTT users are notified about the incoming group call and the functional alias of the group call initiating user is displayed if present. The MCPTT server indicates whether acknowledgement is required for the call and the functional alias of the group call initiating MC service user may be displayed.

The receiving MCPTT clients accept the group call request, and a group call response is sent to the group host MCPTT server. This response may contain an acknowledgement. The conditions for sending acknowledgement may be based on configuration. The response may also contain a functional alias of the responding MC service user, which is verified (valid and activated for the user) by the MCPTT server.

MCPTT server sends the group call response including the selected media parameters to the MCPTT client 1 through the signalling path to inform about successful call establishment. The response may contain the functional alias, which may be displayed.

If the initiating MCPTT user requires the acknowledgement from affiliated MCPTT group members, and the required MCPTT group members do not acknowledge the call setup within a configured time (the "acknowledged call setup timeout"), then the MCPTT server may proceed with or abandon the call and then notify the initiating MCPTT user that the acknowledgements did not include all required members according to group policy from the group configuration. The MCPTT server may notify the initiating MCPTT user of all MCPTT group members who did not acknowledge the group call request within the configured time. This notification may be sent to the initiating MCPTT user by the MCPTT server more than once during the call when MCPTT users join or leave the MCPTT group call.

MCPTT client 1, client 2 and client 3 have successfully established media plane for communication. MCPTT floor participant 1, floor participant 2 and floor participant 3 exchange floor control information e.g., MCPTT client 1 receives the floor granted information over the established media plane assuming implicit floor control request from MCPTT client 1 while at the same time floor participants at other MCPTT client's receive floor taken information. MCPTT client 1 indicates to the MCPTT user that the floor is available to send media, while the other MCPTT clients in the group call will be receiving that media. If audio cut-in policy is enabled for the MCPTT group, floor arbitration follows the logic defined in subclause 10.9.1.5.

It is assumed that MCPTT users on MCPTT client 1, client 2 and client 3 are already part of the ongoing group call (e.g., as a result of pre-arranged group call setup).

MCPTT server would like to release the MCPTT group call which is ongoing e.g., due to hang time expiry, last participant leaving, second last participant leaving, initiator leaving, or minimum number of affiliated MCPTT group members are not present.

MCPTT server identifies the participants of the ongoing group call and generates group call release request to release ongoing session.

MCPTT server sends a group call release request via SIP core towards each participant of the ongoing group call.

MCPTT users are notified about the release of the group call.

MCPTT client(s) receiving group call release request, acknowledge towards the MCPTT server by sending a group call release response.

MCPTT client 1, client 2 and client 3 have successfully released the floor control and media plane resources associated with the group call that is terminated.

MCPTT server determines that MCPTT client 1 which is newly affiliated or coming back from out of coverage has to be invited to join an ongoing group call (late entry).

MCPTT server generates group call request including the information such as MCPTT service identifier (possible for the SIP core to route the request to the MCPTT server), MCPTT group ID of the group invited to join, offer one or more media types and sends towards the MCPTT client 1 via SIP core.

MCPTT user at MCPTT client 1 is notified about the incoming group call.

Upon MCPTT user at MCPTT client 1 accepting the incoming group call request, MCPTT client 1 sends the group call response including the selected media types to the MCPTT server through the signalling path. If the incoming group call request is rejected by the MCPTT client 1, the MCPTT server should not resend the group call request. The group call response may also contain a functional alias of MCPTT client 1.

MCPTT client 1 is successfully added to the ongoing group call and MCPTT users at MCPTT client 1 to MCPTT client n may be notified about the MCPTT client 1 joining the group call and the functional alias of MCPTT client 1 may be displayed.

The floor taken with the information of the current talker is sent to MCPTT client 1.

MCPTT client 1 has necessary information for rejoining an ongoing group call, then the MCPTT client 1 initiates group call rejoin request including the ongoing group call information. The group call rejoin request may contain a functional alias of MCPTT client 1 as selected by the MC service user.

MCPTT server checks whether the MCPTT client 1 can rejoin the ongoing call (e.g. based upon affiliation status) and checks the functional alias, if present.

MCPTT client 1 is informed that the group call rejoin is successful by sending a group call rejoin response. If the ongoing group call is emergency or imminent peril group call, the response shall contain emergency or imminent peril indicator.

MCPTT client 1 is successfully added to the ongoing group call and MCPTT users at MCPTT client 1 to MCPTT client n may be notified about the MCPTT client 1 joining the group call and the functional alias of MCPTT client 1 may be displayed.

The floor taken with the information of the current talker is sent to MCPTT client 1.

MCPTT user 1 indicates to join the group communication for the group. This may include a request to transmit.

MCPTT client 1 sends a group join request with the MCPTT group ID of the desired group. It contains the MCPTT user's MCPTT ID, the MCPTT client media parameters and optionally a functional alias. If there is a request to transmit, then the group joint request contains an indication of an implicit floor request. If the group join request includes an implicit floor request it may also include location information.

The MCPTT server receives the group join request. MCPTT server generates an implicit affiliation (if the MCPTT user is not already affiliated to the group) and verifies that MCPTT user 1 is authorized to affiliate to the group by following the affiliation procedure (subclause 10.8.3 in TS 23.280). If the functional alias is provided only in the group call request, or via binding, the MCPTT server proceeds with the value that is provided. If the functional alias is provided in both the group call request and via binding, it is up to the MCPTT server implementation to determine a value for the functional alias to be used. If present, the MCPTT server checks whether the provided functional alias is allowed to be used and has been activated for the user. If location information was included in the group join request, the MCPTT server checks the privacy policy of the MCPTT user to decide if the location information of MCPTT client 1 can be provided to other users on the call (refer to Annex A.3 "Authorisation to provide location information to other MCPTT users on a call when talking").

The MCPTT server replies with a group join response indicating the acceptance of the group join request and also returns the MCPTT server selected media parameters for the group call in the group join response.

If MCPTT user 1 requests to transmit, the MCPTT server establishes the media plane (if not already established) for the call. The associated floor participants for MCPTT client 1, client 2, and client 3 use the floor control procedure to initiate the call. E.g., the floor participant for MCPTT client 1 receives the MCPTT floor grant. The corresponding floor participants for MCPTT client 2 and MCPTT client 3 receive the MCPTT floor taken. If present, the functional alias of MCPTT client 1, MCPTT client 2 and MCPTT client 3 are displayed where appropriate.

Floor control will continue to be used by the floor participants associated with MCPTT client 1, MCPTT client 2 and MCPTT client 3 for the duration of the call. Media plane signalling using floor control will be used for subsequent calls for the group as long as one or more users are affiliated. If audio cut-in policy is enabled for the MCPTT group, floor arbitration follows the logic defined in subclause 10.9.1.5.

MCPTT server would like to release the MCPTT group call which is ongoing e.g., due to hang time expiry, last participant leaving, second last participant leaving, initiator leaving, or minimum number of affiliated MCPTT group members are not present.

MCPTT server identifies the participants of the ongoing group call and generates group call release request to release the ongoing session.

MCPTT server sends a group call release request towards each participant of the ongoing group call.

MCPTT users are notified about the release of the group call.

Optionally the MCPTT client(s) receiving group call release request, may send a group call release response to the MCPTT server.

MCPTT client 1, client 2 and client 3 release the floor control and media plane resources associated with the group call that is released. Successful release of the group call does not affect the status of affiliation of any of the clients.

MCPTT client 1 sends a group join request with the MCPTT group ID of the desired group. It contains the MCPTT user's MCPTT ID, the MCPTT client media parameters and optionally a functional alias. If there is a request to transmit, then the group joint request contains an indication of an implicit floor request.

The MCPTT server receives the group join request. MCPTT server generates an implicit affiliation (if the MCPTT user is not already affiliated to the group) and verifies that MCPTT user 1 is authorized to affiliate to the group. If the functional alias is provided only in the group call request, or via binding, the MCPTT server proceeds with the value that is provided. If the functional alias is provided in both the group call request and via binding, it is up to the MCPTT server implementation to determine a value for the functional alias to be used. If present, the MCPTT server checks whether the provided functional alias is allowed to be used and has been activated for the user.

The MCPTT server replies with a group join response indicating the acceptance of the group join request.

Media plane between MCPTT client 1 and MCPTT server is established using media plane control signalling.

MCPTT users at MCPTT client 2 and MCPTT client 3 may be notified about the MCPTT client 1 joining the group call. The functional aliases of MCPTT client 1 is displayed, if present.

The MCPTT server sends a floor taken (for the current talker) to MCPTT client 1.

Floor control will continue to be used by the floor participants associated with MCPTT client 1, MCPTT client 2 and MCPTT client 3.

MCPTT client 1 or MCPTT server detects that MCPTT client 1 has returned from out of coverage.

Media plane between MCPTT client 1 and MCPTT server is re-established using media plane control signalling.

MCPTT server sends a floor taken (for the current talker) to MCPTT client 1.

MCPTT users at MCPTT client 2 and MCPTT client 3 may be notified about the MCPTT client 1 returning to the group call. The functional aliases of MCPTT client 1 is displayed, if present.

Floor control will continue to be used by the floor participants associated with MCPTT client 1, MCPTT client 2 and MCPTT client 3.