10.4 Use of MBMS transmissions

23.1803GPPMission critical services support in the Isolated Operation for Public Safety (IOPS) mode of operationRelease 17TS

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

10.4.1 General

An IOPS MC connectivity function can provide support for group communications based on MBMS transmissions. MBMS transmissions can be used for the downlink delivery of MC service application signalling and media to the MC service UEs over MBMS bearers.

The use of MBMS transmissions in the IOPS mode of operation are based on the related information flows and procedures specified in 3GPP TS 23.280 [3], 3GPP TS 23.379 [5], and 3GPP TS 23.282 [6].

10.4.2 Information flows

10.4.2.1 MapIOPSGroupToBearer (IP connectivity functionality)

Table 10.4.2.1-1 describes the information flow to associate a group session based on the IP connectivity functionality to an MBMS bearer. It is sent from the IOPS MC connectivity function to the MC service client.

Table 10.4.2.1-1: MapIOPSGroupToBearer (IP connectivity functionality)

Information element	Status	Description
IOPS MC service group ID	M	This element identifies the IOPS MC service group, in which the group session is started.
Media stream identifier	M	This element identifies the media stream of the SDP used for the group session (e.g. MBMS subchannel).
TMGI (NOTE)	O	The MBMS bearer identifier if the media of the group session is not sent on the same MBMS bearer as this MapIOPSGroupToBearer message.
Session acknowledgement indicator	O	Indication that the group session requires acknowledgement from receiving MC service clients.
NOTE: TMGI shall be present if this message is sent over a different MBMS bearer than the media of the group session; TMGI may be present if this message is sent over the same MBMS bearer as the media of the group session.

10.4.2.2 UnmapIOPSGroupFromBearer (IP connectivity functionality)

Table 10.4.2.2-1 describes the information flow to disconnect a group session based on the IP connectivity functionality from an MBMS bearer. It is sent from the IOPS MC connectivity function to the MC service client.

Table 10.4.2.2-1: UnmapIOPSGroupFromBearer

Information element	Status	Description
IOPS MC service group ID	M	This element identifies the IOPS MC service group, in which the group session is started.

10.4.3 Use of pre-established MBMS bearers

The MC services in the IOPS mode of operation shall support the procedure for using pre-established MBMS bearers as specified 3GPP TS 23.280 [3] with the following clarification:

– The MC service server is the IOPS MC connectivity function.

The MCPTT service shall use the MCPTT-IOPS-2, MCPTT-IOPS-4, and MC-IOPS-6 reference points for this procedure.

The MCData service shall use the MCData-IOPS-2, MCData-IOPS-4, and MC-IOPS-6 reference points for this procedure.

The IOPS MC system may use pre-established MBMS bearers for distributing the media associated to group sessions. Depending on the capacity of the MBMS bearer, the bearer can be used to broadcast one or more group sessions in parallel.

10.4.4 Use of dynamic MBMS bearer establishment

The MC services in the IOPS mode of operation shall support the procedure for using dynamic MBMS bearers as specified 3GPP TS 23.280 [3] with the following clarification:

– The MC service server is the IOPS MC connectivity function.

The MCPTT service shall use the MCPTT-IOPS-2, MCPTT-IOPS-4, and MC-IOPS-6 reference points for this procedure.

The MCData service shall use the MCData-IOPS-2, MCData-IOPS-4, and MC-IOPS-6 reference points for this procedure.

The IOPS MC system may use dynamic MBMS bearer establishment for distributing the media associated to group sessions.

10.4.5 Group session connect and disconnect over MBMS (IP connectivity functionality)

10.4.5.1 General

MBMS bearers can be used for group sessions based on the IP connectivity functionality. One MBMS bearer can be associated to one or more specific groups or group sessions. Before sending packets related to a group session, i.e. signalling and media, over an MBMS bearer, the IOPS MC connectivity function transmits the association information between the group session and the MBMS bearer. When the group session over the MBMS bearer is finished, this temporary association information of a group session to specific resources on a MBMS bearer is undone. Prior to the association of a group session to an MBMS bearer the MBMS bearer is activated and announced to the MC service clients.

10.4.5.2 Procedure

10.4.5.2.1 Group Session connect over MBMS

In figure 10.4.5.2.1-1 the MC service client 1 is the client that initiates a group session, e.g. an MCPTT client initiating a group call. The MC service client 1 may be within the MBMS service area. The MC service clients 2 … n represent MC service clients, e.g. MCPTT clients, receiving the group session packets over an MBMS bearer. There may be other receiving MC service clients both over unicast bearers and over this or other MBMS bearer(s), however, they are not illustrated in this figure.

Pre-conditions:

– The MC service user profile used for the IOPS mode of operation is pre-provisioned in the MC service UEs

– The IOPS MC service group ID and its associated IOPS group IP multicast address are pre-configured in the MC service clients

– The MC service users have an active PDN connection to the IOPS MC connectivity function for the communication based on the IP connectivity functionality

– The MC service users are discovered by the IOPS MC connectivity function to support MC services based on the IP connectivity functionality

Figure 10.4.5.2.1-1: Group session connect on MBMS bearer (IP connectivity functionality)

1. Activation and announcement of MBMS bearer availability.

2. MC user at the MC service client 1 wants to initiate an MC service group session with a specific IOPS MC service group based on the IP connectivity functionality.

3. The MC service client 1 transmits the related group session packets via the IOPS MC connectivity function targeting the IOPS MC service group (i.e. using the corresponding IOPS group IP multicast address)

4. The IOPS MC connectivity function determines that the received packets correspond to a group session. Therefore, the IOPS MC connectivity function transmits a MapIOPSGroupToBearer message over a previously established MBMS bearer to all users monitoring the MBMS bearer. The MapIOPSGroupToBearer message includes association information between the group session and the MBMS bearer. It includes the corresponding IOPS MC service group ID associated to the IOPS group IP multicast address related to the group session.

5. The IOPS MC connectivity function distributes the received group session packets from the MC service client 1 to other MC service clients (e.g. MC service clients 2 … n) over the MBMS bearer.

NOTE: MC service clients receiving the group session packets over the MBMS bearer only decode the packets that are addressed to their pre-configured IOPS group IP multicast address(es). Otherwise, the MC service clients discard the packets.

10.4.5.2.2 Group session disconnect over MBMS

Figure 10.4.5.2.2-1 shows the high level procedure where an UnmapIOPSGroupFromBearer message is transmitted from the IOPS MC connectivity function to MC service clients to indicate that a group session is being disconnected or dissociated from the MBMS bearer.

Figure 10.4.5.2.2-1: Group session disconnect on MBMS bearer (IP connectivity functionality)

1. A group session based on the IP connectivity functionality is ongoing; the group session packets received from the MC service client 1 are distributed over MBMS bearer to other MC service clients within the system.

2. The IOPS MC connectivity function has determined to disconnect the group session from the MBMS bearer for the MC service clients within the system.

NOTE: The IOPS MC connectivity function may decide to disconnect a group session from an MBMS bearer if group session packets are not anymore received addressing the corresponding IOPS MC service group (or IOPS group IP multicast address).

3. An UnmapGroupFromBearer message is transmitted from the IOPS MC connectivity function to the MC service clients and possibly to the MC service client 1 (if it is within the MBMS coverage area) on MBMS bearer(s).