Entities within the application plane of an IOPS MC system provide application specific functions to support MC services in the IOPS mode of operation.

The IOPS connectivity client functional entity provides support for enabling that a user at the MC service client is registered and discovered by the IOPS MC system in the IOPS mode of operation. This functional entity is located in the MC service UE.

The IOPS MC connectivity function entity provides supporting MC services in the IOPS mode of operation. It includes registering and discovering users within the IOPS MC system. The IOPS MC connectivity functional entity represents a specific instantiation of the GCS AS described in TS 23.468 for EPS or Application Function (AF) for 5GS to manage unicast and multicast transmissions for group communication related sessions. The IOPS MC connectivity function entity is supported by the signalling application server functional entity of the signalling control plane.

The IOPS distribution function entity provides support for distributing the IP packets containing the MC service application data received from a MC service UE in the IOPS mode of operation. By means of information provided by the IOPS MC connectivity function (e.g. IP addresses, transport layer ports), it will provide the following functionality:

• receiving uplink IP transmissions from the MC service UE by means of the MCPTT-IOPS-3 reference point for MCPTT and the MCData-IOPS-3 reference point for MCData;
• distributing the related IP packets via downlink IP unicast transmissions to MC service UEs by means of the MCPTT-IOPS-3 reference point for MCPTT and the MCData-IOPS-3 reference point for MCData;
• distributing the related IP packets via downlink IP multicast transmissions to MC service UEs by means of the MCPTT-IOPS-4 reference point for MCPTT and the MCData-IOPS-4 reference point for MCData.

The MC service client functional entity, e.g. a MCPTT client and a MCData client, supporting the IOPS mode of operation acts as the user agent for the corresponding MC service transactions as well as all IOPS related application transactions.

The signalling user agent client functional entity supports at the MC service client all required transactions related to the IOPS discovery. This includes supporting registration, publication, subscription and notification events.

The signalling application server functional entity supports at the IOPS MC system all required transactions related to the IOPS discovery. This includes supporting registration, publication, subscription and notification events.

The MC-IOPS-1 reference point, which exists between the IOPS MC connectivity function and the IOPS connectivity client, is used for IOPS related application signalling (e.g. registration, publication, subscription and notification events). The MC-IOPS-1 reference point utilizes the MC-IOPS-X1 reference point for transport and routing of the IOPS related signalling.

The MCPTT-IOPS-2 reference point, which exists between the IOPS MC connectivity function and the MCPTT client, is used to communicate signalling related to the broadcast/multicast sessions utilized for multicast transmissions, e.g. MBMS bearer announcement or 5G MBS session announcement in the IOPS mode of operation.

The MCData-IOPS-2 reference point, which exists between the IOPS MC connectivity function and the MCData client, is used to communicate signalling related to the broadcast/multicast sessions utilized for multicast transmissions, e.g. MBMS bearer announcement or 5G MBS session announcement in the IOPS mode of operation.

The MCPTT-IOPS-3 reference point, which exists between the IOPS distribution function and the MCPTT client, is used for IP unicast transmissions in uplink and downlink. The MCPTT-IOPS-3 reference point uses the SGi reference point as defined in TS 23.002 or N6 reference point as defined in TS 23.501.

The MCData-IOPS-3 reference point, which exists between the IOPS distribution function and the MCData client, is used for IP unicast transmissions in uplink and downlink. The MCData-IOPS-3 reference point uses the SGi reference point as defined in TS 23.002 or N6 reference point as defined in TS 23.501.

The MCPTT-IOPS-4 reference point, which exists between the IOPS distribution function and the MCPTT client, is used for IP multicast transmissions in downlink. The MCPTT-IOPS-4 reference point uses the MB2-U reference point as defined in TS 23.468 or Nmb8/ Nmb6 reference point as defined in TS 23.247.

The MCData-IOPS-4 reference point, which exists between the IOPS distribution function and the MCData client, is used for IP multicast transmissions in downlink. The MCData-IOPS-4 reference point uses the MB2-U reference point as defined in TS 23.468 or Nmb8/ Nmb6 reference point as defined in TS 23.247.

The MC-IOPS-5 reference point, which exists between the IOPS MC connectivity function and the IOPS 3GPP system, is used to obtain unicast sessions with appropriate QoS from the IOPS 3GPP system. The MC-IOPS-5 reference point utilizes the Rx interface of the EPS according to TS 23.203 , or N5 interface of 5GS according to TS 23.503.

The MC-IOPS-6 reference point, which exists between the IOPS MC connectivity function and the 3GPP system (IOPS EPS), is used to request the allocation and activation of broadcast/multicast transport resources, i.e. MBMS bearers or 5G MBS sessions, during the IOPS mode of operation. The MC-IOPS-6 reference point uses the MB2-C interface as defined in TS 23.468, or Nmb10, Nmb13, or N33, as defined in TS 23.247.

The MC-IOPS-X1 reference point, which exists between the signalling application server and the signalling user agent client, is used to support the IOPS related application signalling (e.g. registration, publication, subscription and notification events).