9.4 Off-network Broadcast group call

24.2813GPPMission Critical Video (MCVideo) signalling controlProtocol specificationRelease 18TS

Tools: ARFCN - Frequency Conversion for 5G NR/LTE/UMTS/GSM

9.4.1 General

9.4.2 Basic call control

9.4.2.1 General

9.4.2.2 Broadcast group call control state machine

The figure 9.4.2.2-1 gives an overview of the main states and transitions on the UE for broadcast group call call control.

Figure 9.4.2.2-1: Broadcast group call control state machine

9.4.2.3 Broadcast group call Control states

9.4.2.3.1 B1: start-stop

This state exists for UE, when the UE is not part of an ongoing broadcast group call.

9.4.2.3.2 B2: in-progress broadcast group call

This state exists for UE, when the UE is part of an ongoing broadcast group call.

9.4.2.3.3 B3: pending user action

This state exists for the UE, when the UE has presented a notification to the MCVideo user for the received GROUP CALL BROADCAST message, is waiting for a response and is not expected to send confirm indication.

9.4.2.3.4 B4: ignoring same call ID

This state exists for UE, when the group call was rejected or released and GROUP CALL BROADCAST messages continue being received.

9.4.2.4 Procedures

9.4.2.4.1 User initiating a broadcast group call

When in the "B1: start-stop" state, upon the indication from MCVideo user to initiate the broadcast group call, the MCVideo client:

1) shall generate an SDP body as specified in clause 9.3.1.1.2 and store it as the SDP body of the call;

2) shall generate a random number with uniform distribution between 0 and 65535 and store it as the call identifier of the call;

3) shall store own MCVideo user ID as the originating MCVideo user ID of the call;

4) shall store "BROADCAST GROUP CALL" as the current call type;

5) shall generate a GROUP CALL BROADCAST message as specified in clause 17.1.18. In the GROUP CALL BROADCAST message, the MCVideo client:

a) shall set the Call identifier IE to the stored call identifier of the call;

b) shall set the Call type IE to the stored current call type;

c) shall set the Originating MCVideo user ID IE to the stored originating MCVideo user ID of the call;

d) shall set the MCVideo group ID IE to the stored MCVideo group ID of the call; and

e) shall set the SDP IE to the stored SDP body of the call;

6) shall set the ProSe per-packet priority to the value corresponding to MCVideo off-network broadcast callas described in 3GPP TS 24.483 [4];

7) shall start transmission control as originating transmission participant as described specified in clause a.b in 3GPP TS 24.581 [5];

8) shall send the GROUP CALL BROADCAST message as specified in clause 9.3.1.1.1;

9) shall establish a media session based on the stored SDP body of the call;

10) shall start timer TFB2 (broadcast retransmission); and

11) shall enter the "B2: in-progress broadcast group call" state.

9.4.2.4.2 Terminating UE receiving a GROUP CALL BROADCAST message when not participating in the in-progress broadcast group call

When in the "B1: start-stop" state, upon receiving a GROUP CALL BROADCAST message with the Call identifier IE not matching any in-progress broadcast group call, the MCVideo client:

1) shall store the value of the Call identifier IE of the GROUP CALL BROADCAST message as the call identifier of the call;

2) shall store the value of the Call type IE of the GROUP CALL BROADCAST message as the received current call type;

3) shall store the value of the SDP IE of the GROUP CALL BROADCAST message as the SDP body of the call;

4) shall store the value of the Originating MCVideo user ID IE of the GROUP CALL BROADCAST message as the originating MCVideo user ID of the call;

5) shall store the value of the MCVideo group ID IE of the GROUP CALL BROADCAST message as the MCVideo group ID of the call;

6) if the terminating UE is configured that the terminating MCVideo user acknowledgement is required upon a terminating call request reception:

i) shall start timer TFB3 (waiting for the user); and

ii) shall enter the "B3: pending user action" state; and

7) if the terminating UE is configured that the terminating MCVideo user acknowledgement is not required upon a terminating call request reception:

i) shall establish a media session based on the stored SDP body of the call;

ii) shall start transmission control as terminating transmission participant as specified in clause a.b in 3GPP TS 24.581 [5];

iii) shall start timer TFB1 (max duration); and

iv) shall enter the "B2: in-progress broadcast group call" state.

9.4.2.4.3 MCVideo user accepts the terminating call

When in the "B3: pending user action" state, upon indication from the MCVideo user to accept the incoming broadcast group call, the MCVideo client:

1) shall establish a media session based on the stored SDP body of the call;

2) shall start transmission control as terminating transmission participant as described specified in clause a.b in 3GPP TS 24.581 [5];

3) shall stop timer TFB3 (waiting for the user);

4) shall start timer TFB1 (max duration); and

5) shall enter the "B2: in-progress broadcast group call" state.

9.4.2.4.4 MCVideo user rejects the terminating call

When in the "B3: pending user action" state, upon an indication from the MCVideo user to reject the incoming broadcast group call, the MCVideo client:

1) shall stop timer TFB3 (waiting for the user); and

2) shall enter the "B4: ignoring same call ID" state.

9.4.2.4.5 MCVideo user does not act on terminating call

When in the "B3: pending user action" state, upon expiration of timer TFB3 (waiting for the user), the MCVideo client:

1) shall enter the "B4: ignoring same call ID" state.

9.4.2.4.6 Terminating user releasing the call

When in the "B2: in-progress broadcast group call" state, upon an indication from the terminating MCVideo user to release the in-progress broadcast group call, the MCVideo client:

1) shall release the media session;

2) shall stop transmission control; and

3) shall enter the "B4: ignoring same call ID" state.

9.4.2.4.7 Originating user releasing the call

When in the "B2: in-progress broadcast group call" state, upon an indication from the originating MCVideo user to release the in-progress broadcast group call, the MCVideo client:

1) shall release the media session;

2) shall generate a GROUP CALL BROADCAST END message as specified in clause 17.1.19. In the GROUP CALL BROADCAST END message, the MCVideo client:

a) shall set the Call identifier IE to the stored call identifier of the call;

b) shall set the Originating MCVideo user ID IE to the stored originating MCVideo user ID of the call; and

c) shall set the MCVideo group ID IE to the stored MCVideo group ID of the call;

3) shall send the GROUP CALL BROADCAST END message as specified in clause 9.3.1.1.1;

4) shall stop timer TFB2 (broadcast retransmission);

5) shall stop transmission control; and

6) shall enter the "B1: start-stop" state.

9.4.2.4.8 Receiving GROUP CALL BROADCAST END message

When in the "B2: in-progress broadcast group call" state or "B4: ignoring same call ID" state, upon receiving GROUP CALL BROADCAST END message with the same Call identifier IE as the stored call identifier, the MCVideo client:

1) shall release media session;

2) shall stop transmission control, if running; and

3) shall enter the "B1: start-stop" state.

9.4.2.4.9 Originating UE retransmitting GROUP CALL BROADCAST message

When in the "B2: in-progress broadcast group call" state, upon expiry of timer TFB2 (broadcast retransmission), the MCVideo client:

1) shall generate a GROUP CALL BROADCAST message as specified in clause 17.1.18. In the GROUP CALL BROADCAST message, the MCVideo client:

a) shall set the Call identifier IE to the stored call identifier of the call;

b) shall set the Call type IE to the stored current call type;

c) shall set the Originating MCVideo user ID IE to the stored originating MCVideo user ID of the call;

d) shall set the MCVideo group ID IE to the stored MCVideo group ID of the call; and

e) shall set the SDP IE to the stored SDP body of the call;

2) shall send the GROUP CALL BROADCAST message as specified in clause 9.3.1.1.1;

3) shall restart timer TFB2 (broadcast retransmission); and

4) shall remain in the "B2: in-progress broadcast group call" state.

9.4.2.4.10 Ignoring same call ID

When in the "B4: ignoring same call ID" state, upon receiving GROUP CALL BROADCAST message and if the call identifier in GROUP CALL BROADCAST message matches with the stored call identifier the MCVideo client:

1) shall restart timer TFB1 (max duration); and

2) shall remain in "B4: ignoring same call ID" state.

9.4.2.4.11 Releasing the call

When in the "B2: in-progress broadcast group call" state or "B4: ignoring same call ID" state, upon expiry of timer TFB1 (max duration) the MCVideo client:

1) shall release the media session;

2) shall clear the stored call identifier;

3) shall stop transmission control, if running; and

4) shall enter the "B1: start-stop" state.