10.5.4 Floor override without using floor revoked on an interworking group

23.2833GPPMission Critical Communication Interworking with Land Mobile Radio SystemsRelease 18TS

This procedure describes the case where a transmitting radio cannot be signalled that the floor has been taken or revoked. Within the context of interworking between MCPTT and LMR systems, this condition can occur due to both MCPTT and LMR users obtaining the floor simultaneously, or the floor granted to an LMR user is taken by an MCPTT user.

Figure 10.5.4‑1 shows the high-level procedure where an MCPTT session is already established between the floor participants (with floor granted to an LMR user represented by the IWF) and the floor control server (with an override based on priority and configured to permit the transmission of overridden floor participant from the IWF). The group is defined in the MCPTT system and the MCPTT Server is the floor control server. Only two UEs involved in the session are shown for simplicity.

Pre-conditions:

1. The MCPTT floor control server has been configured to support override.

2. The override supported in this case permits both the overridden floor participant and the overriding floor participant to be transmitting.

3. An MCPTT session is established between an MCPTT client, the interworked system, and MCPTT server.

4. Session is ongoing.

Figure 10.5.4‑1: Floor override (overridden continues to transmit) during an interworking session

1. It is assumed that the floor participant B (represented by the IWF in figure 10.5.4‑1) has been given the floor and is transmitting voice media.

2. Floor participant A, having a floor priority which is relatively higher than that of floor participant B, wants to send voice media over the session.

3. Floor participant A sends a floor request message to the floor control server.

4. The floor control server determines to accept the floor request from floor participant A based on arbitration result e.g., according to the floor priority information that is received in the floor request message.

5a. Floor control server responds with a floor granted message to floor participant A.

5b. Floor control server sends a floor taken message to the other floor participants (via the IWF). Floor participant B continues transmitting the (overridden) voice media transmission.

NOTE 1: All other floor participants (not shown) that are part of this group call receive a floor taken message, so that the other floor participants learn who the newly granted talker (overriding) is.

6a. The floor granted causes the user of floor participant A to be notified.

6b. Floor participant B cannot be notified of the status because it is unable to receive the message and continues transmitting.

7. Floor participant A (overriding) starts sending voice media over the session established beforehand.

NOTE 2: Floor participant B is still sending voice (overridden). The list of floor participants that receive the overriding, overridden, or both transmissions is based on configuration.

NOTE 3: When floor participant A stops transmitting, if floor participant B is still sending voice, then the floor is granted back to floor participant B and audio is routed to all current floor participants.