Content for  TS 23.379  Word version:  19.4.0

When an MCPTT user using a ProSe-enabled UE wants to communicate with a specific MCPTT group using ProSe capabilities, the MCPTT client enables the use of the ProSe layer procedures for public safety, as specified in TS 23.303. The MCPTT client obtains configuration data such as the user info ID of the calling MCPTT user and the ProSe Group IP multicast address and ProSe Layer-2 Group ID associated to the target MCPTT group (as described in clause 8.1.3.2 of TS 23.280), and provides it to the ProSe layer. The ProSe Layer-2 Group ID of the target MCPTT group may be used by the ProSe layer as the target group info and the discovery group ID (defined in TS 23.303). Prior to the establishment of an off-network group call, a group member discovery procedure may be initiated to identify whether other members of the target MCPTT group are in the proximity of the calling MCPTT user, as described in the ProSe direct discovery for public safety use procedure in TS 23.303. The establishment of an off-network group call using the ProSe capability is based on the one-to-many ProSe direct communication procedure for public safety use described in TS 23.303. Off-network group calls can use pre-defined configuration information provided to MCPTT clients prior to the off-network group call or configuration information that is transmitted to MCPTT clients during group call setup or late entry procedures. If off-network group configuration information is pre-defined (e.g. codec to be used) and provided to the MCPTT clients prior to the off-network group call (e.g. as part of group metadata), the MCPTT client will be able to participate in the off-network group call without needing to follow the group call setup or late joining procedures as they will be able to receive the media and signalling without the need for the announcement or invitation. If off-network group configuration information is not pre-defined or provided, call parameters need to be transmitted to MCPTT clients via group call announcement or invitation.

The flow in Figure 10.6.3.3-1 illustrates the control plane procedures for MCPTT group call establishment for off-network. The procedure describes how an MCPTT client initiates an MCPTT group call with other MCPTT client within the off-network radio coverage and how the group call is established. Pre-conditions:

• It is assumed that information for ProSe direct communications corresponding to the mappings of MCPTT group ID and ProSe Layer-2 Group ID (see subclause 8.1.3.2 in TS 23.280) are pre-configured;
• It is assumed that a multicast IP address and port for the call setup signalling are pre-configured;
• All messages exchanged between the MCPTT clients for the MCPTT group follows ProSe direct communications as defined in TS 23.303; and
• The MCPTT users of MCPTT client 1, 2 and 3 belong to the same MCPTT group.

Figure 10.6.3.4-1 illustrates the control plane procedures for the passive MCPTT client to join the on-going MCPTT group call. The passive MCPTT client does not initiate to establish an MCPTT group call, but receives the group call announcement to be transferred periodically. When receiving the announcement message with parameters for media transfer, the passive MCPTT client configures the parameter to receive the voice and joins the announced MCPTT group call. This procedure happens after the MCPTT group call is established. The group call announcement including the parameters for the media transfer has been performed periodically, in order for the MCPTT client later to join the MCPTT group call. The MCPTT client 4 enters the coverage of the MCPTT group call lately.

Figure 10.6.3.5-1 illustrates the control plane procedures for an MCPTT client to join an on-going MCPTT group call. When entering the coverage of on-going group call, new MCPTT client may send group call setup announcement message with on-going group call id. Upon receiving the group call setup announcement, the MCPTT client as a participant of on-going MCPTT group call sends parameters for media transfer to the newly entered MCPTT client (entrant) to join the on-going MCPTT group call. When receiving the parameters for media transfer of on-going MCPTT group call, the MCPTT client configures the parameters to receive the voice and becomes the participant of the on-going MCPTT group call.

MCPTT client 4 joins and becomes participants of the on-going MCPTT group call.

Figure 10.6.3.6-1 illustrates the control plane procedures for an MCPTT client to immediately join an on-going MCPTT group call. Upon the detection of a new entrant, the MCPTT client that is the current talker (floor arbitrator) immediately sends the group call announcement. When receiving the group call announcement message with parameters for media transfer, that MCPTT client configures the parameters to receive the voice and joins the on-going MCPTT group call. Pre-conditions:

1. There is on-going group call. MCPTT client 1 is the current talker and therefore the floor arbitrator.

If the on-going MCPTT group call is inactive for a specific duration, the participating MCPTT clients release the MCPTT group call by themselves.

Group call on group-broadcast group and user-broadcast group are handled without distinction in off-network. Figure 10.6.3.8.1-1 illustrates the control plane procedures for broadcast group call in off-network.