The AF should be authorized by the 5GC for delivering MBS data to the 5GC and/or interacting with the 5GC. For signalling exchange with the 5GC, the NEF perform authorization to the external AF for determination of whether the interaction with the 5GC is allowed or not.

The following authorizations are defined:

1. Whether the UE is authorized to use the Multicast service in the PLMN.
2. The authorization for a UE of receiving the content of a specific multicast MBS session.

A Multicast MBS session may be "open to any UEs". For a Multicast MBS session, it is required that the 5GC authorizes the UE based on the MBS subscription data and whether the Multicast MBS session is "open to any UEs", which are preconfigured, or provided by the AF (see clause 7.2.9). The procedure for UE authorization is a part of UE join procedure and is described in clause 7.2.1.3.

A Local MBS service is an MBS service provided in one MBS service area. A location dependent MBS service is an MBS service provided in several MBS service area(s). An MBS service area is identified by a cell list or a tracking area list. The MBS service area could be geographical area information or civic address information, and NEF/MBSF translates the location information to Cell ID list or TAI list as MBS service area, see clause 7.1.1.2. The MBS service area may be updated by the AF for both multicast MBS sessions and broadcast MBS sessions as specified in clause 7.1.1.6. For more details, refer to clause 7.2.4 for multicast MBS session and refer to clause 7.3.4 for broadcast MBS session.

For a local MBS service, only UEs within the MBS service area may receive content data, while UEs outside the MBS service area are not allowed to receive location specific content. For multicast MBS service, UEs outside the MBS service area are not allowed to join the MBS service, and the network shall not deliver location specific content anymore to the UEs moved out of the MBS service area. Depending on policy, for the multicast MBS service the network may remove UEs outside the MBS service area of the MBS session from the MBS Session Context after a grace period. The SMF may subscribe at the AMF to notifications about "UE moving in or out of a subscribed" "Area Of Interest" event. For multicast communication, local MBS may be supported via 5GC Individual MBS traffic delivery towards RAN nodes not supporting MBS. If the SMF obtains a notification that the UE is no longer in the MBS service area, the SMF terminates the 5GC Individual MBS traffic delivery towards the UE. The UE shall be able to obtain service area information of the local multicast service via MBS service announcement or via NAS signalling (UE Session Join Accept/Reject including Cell ID list or TAI list). If the UE Session Join procedure fails due to the UE being outside the MBS service area, the UE does not attempt to join the Multicast MBS session again until the UE moves inside the MBS service area. When the UE Session Join succeeds and if the Multicast MBS session is inactive, the UE does not perform monitoring the session activation notification and any other information related to the Multicast MBS session identified by an MBS Session ID over the radio if outside the MBS service area.

A location dependent MBS is identified by MBS Session ID, and provided in several MBS service areas. The location dependent MBS service enables distribution of different content data to different MBS service areas. The same MBS Session ID is used but a different Area Session ID is used for each MBS service area. The Area Session ID is used, in combination with MBS Session ID, to uniquely identify the service area specific part of the content data of the MBS service within 5GS. The network supports the location dependent content distribution for the location dependent MBS services, while UEs are only aware of the MBS Session ID (i.e. UEs are not required to be aware of the Area Session IDs). When UE moves to a new MBS service area, content data from the new MBS service area shall be delivered to the UE, and the network ceases to deliver the content data from the old MBS service areas to the UE. For multicast MBS service, UEs outside all MBS service areas of the location dependent MBS session are not allowed to join the MBS service. When UE moves out of an MBS service area and there is no other MBS service area for the MBS session, the network ceases to deliver the content data to the UE. Depending on policy, for the multicast MBS service the network may remove UEs outside all MBS service areas of the location dependent MBS Session from the multicast MBS Session Context after a grace period The SMF may subscribe at the AMF to notifications about UE moving in or out of all MBS service areas of the location dependent MBS session. For multicast communication towards an NG-RAN supporting MBS, the NG-RAN node handles mobility of UEs within the MBS session between MBS service areas served by the same NG-RAN without interaction with SMF. For multicast communication, location dependent MBS services may be supported via 5GC Individual MBS traffic delivery towards RAN nodes not supporting MBS. If the SMF determines that the UE is in another MBS service area of the Multicast MBS session, the SMF configures the UPF to send multicast data relating to the new MBS service area towards the UE. Information about different MBS service areas for a location dependent MBS service may be provided by one or several AFs or may be configured. The MBS Service Information provided is specified in clause 6.14. Different ingress points for location dependent points for the MBS session are supported for different MBS service area dependent content of the MBS session; different MB-UPF may be assigned for different MBS service areas within the same MB-SMF Service Area for an MBS session. For broadcast communication, if MBS service areas covering different MB-SMF Service Areas are required, different MB-SMFs should be assigned for different MB-SMF service areas for an MBS session, and in this case the MB-SMF involved in the MBS Session should be able to accept TMGI value allocated by other MB-SMF(s). The Area Session ID is allocated by MB-SMF in MBS Session creation procedure. MB-SMF allocates Area Session ID for each MBS services area which is unique within the MBS session. MB-SMF needs to further ensure there is no MBS service area overlapping with other MBS service areas that share the same MBS Session ID. The same QoS applies to all MBS service areas of a location dependent MBS Session.

The mobility of multicast MBS service is supported when:

• The UE moves from a NG-RAN node that supports MBS to a target NG-RAN node that supports MBS; or
• The UE moves from a NG-RAN node that supports MBS to a target NG-RAN node that does not support MBS and vice versa.

During the mobility from a NG-RAN node that supports MBS to a target NG-RAN node that supports MBS, or between a NG-RAN node that supports MBS and a target NG-RAN node that does not support MBS, minimization of data loss should be supported, see clause 7.2.3.5 for details. To support Handover from NG-RAN node that supports MBS to a target NG-RAN node that supports MBS:

• If the shared delivery for the MBS session has not been established towards target NG-RAN, the target NG-RAN establishes the shared delivery for the MBS Session with MB-SMF and MB-UPF.

To support Handover from NG-RAN node that supports MBS to a target NG-RAN node that does not support MBS:

• mapping information about unicast QoS flows for multicast data transmission and the information of associated multicast QoS flows are provided to the NG-RAN node. This is already performed during the PDU session modification procedure for the PDU session associated with the MBS session when the UE joins the MBS Session;
• during the handover procedure, the delivery method is switched from 5GC Shared MBS traffic delivery method to 5GC Individual MBS traffic delivery method, i.e. the N3 tunnel of the PDU Session for 5GC Individual MBS traffic delivery needs to be established towards the target NG-RAN node. The SMF realizes that the target NG-RAN node does not support MBS.
• the SMF and the MB-SMF shall activate the GTP tunnel between the UPF and the MB-UPF for 5GC Individual MBS traffic delivery method, if needed.

To support Handover from a NG-RAN node that does not support MBS to a target NG-RAN node that supports MBS:

• The PDU sessions, including the one associated with the MBS session and used for 5GC Individual MBS traffic delivery, are handed over to the target NG-RAN node.
• SMF triggers mode switch, i.e. from 5GC Individual MBS traffic delivery method to 5GC shared MBS traffic delivery method.
  - When the MBS Session Context is given to the target NG-RAN node by the SMF, if the shared delivery for the MBS session has not been established towards target NG-RAN, the target NG-RAN establishes the shared delivery for the MBS Session with MB-SMF and MB-UPF.
• The 5GC terminates the 5GC Individual MBS traffic delivery and changes to the 5GC shared MBS traffic delivery.

The UE receives the same Broadcast MBS service in the target NG-RAN if the same MBS session is established with 5GC Shared MBS traffic delivery method in the target NG-RAN node.

The UDM stores the MBS subscription information. The MBS subscription data for a UE is included within the UE subscription data. At any time, the operator may change the subscription for multicast services in the UDM. The MBS subscription data in UE subscription data contains the following information:

• MBS authorization information that gives the user permission to use multicast services
  • Whether the UE is authorized to use the multicast MBS service.
  • Optionally, MBS Session ID(s) of the Multicast MBS session(s) that the UE is allowed to join.
• Optionally, MBS assistance information indicating that a UE is preferred to be kept connected when the related MBS Session the UE joined is active, which contains the following information:
  • MBS Session ID(s).

The MBS subscription data is provided by the UDM to the SMF during or after the establishment procedure of PDU Session associated with Multicast MBS session(s) using Nudm_SDM service for subscription data type "MBS subscription data" as defined in clause 7.2.1.2. During multicast session join procedure, the SMF retrieves MBS Session information from the MB-SMF, and authorizes the MBS Session join request for the UE based on MBS subscription data of the UE received from UDM and the Any UE indication (i.e. whether the Multicast MBS session is "open to any UEs") received from MB-SMF as described in clause 7.2.1.3. The UDR stores the MBS data, which may be updated by the UDM or the AF/NEF as specified in clause 4.15.6.2 of TS 23.502, i.e. AF may provision Multicast MBS Session Authorization information for the MBS as described in clause 7.2.9.

The information stored in the UDM as defined in clause 5.2.3.3.1 of TS 23.502 is extended as follows:

• MBS subscription data for a UE as part of UE subscription data, as defined in Table 6.4.2-1, with keys defined in Table 6.4.2-2.

The MBS information may be stored in the UDR by the UDM as part of the subscription data, as defined in clause 5.2.12.2.1 of TS 23.502.

1. MBS data as defined in Table 6.4.2-1, with keys defined in Table 6.4.3-1.

The MBS session ID is used to identify a Multicast/Broadcast MBS Session by the 5G system on external interface towards AF and between AF and UE, and towards the UE. MBS Session ID may have the following types:

• TMGI (for broadcast and multicast MBS sessions);
• source specific IP multicast address (for multicast MBS sessions).

If a multicast MBS session is provided within an SNPN, the multicast MBS session can still be identified by a (globally unique) source specific IP multicast address or TMGI. In 5GS internal signalling the PLMN ID, included in TMGI, is complemented with the NID to identify an SNPN. Source specific IP multicast address or TMGI may be used as MBS Session ID in NAS messages exchange between a UE and a CN when the UE requests to join/leave a Multicast MBS session. For multicast MBS sessions that the UE joined with a source specific IP multicast address, a TMGI is also allocated by 5GC and is sent to the UE and used in other signalling messages between RAN, CN and UE. Details see clause 7.2.1.3. The UE shall be able to obtain at least one MBS Session ID via MBS service announcement. For multicast MBS sessions, a source specific IP multicast address can be assigned by external AFs.

TMGI (Temporary Mobile Group Identity) is defined in TS 23.003 and is used to be able to identify a broadcast MBS Session or a multicast MBS session. In SNPN (Stand-alone Non-Public Network), TMGI is used together with NID (Network Identifier) defined in TS 23.003 to identify an MBS Session.

The source specific IP multicast address is used to identify an Multicast MBS session and consists of two IP addresses, one is an IP unicast address used as source address in IP packets for identifying the source of the multicast service (e.g. AF/AS), the other is an IP multicast address used as destination address in related IP packets for identifying a multicast communication service associated with the source.

The MBS Frequency Selection Area (FSA) ID is used for broadcast MBS session to guide the frequency selection of the UE. MBS FSA ID identifies a preconfigured area within, and in proximity to, which the cell(s) announces the MBS FSA ID and the associating frequency (details see TS 38.300). MBS FSA ID and their mapping to frequencies are provided to RAN nodes via OAM. Based on this configuration, RAN nodes announce in SIBs over the radio interface information about the MBS FSA IDs and frequencies. When a broadcast MBS session is created, the AF may provide MBS FSA ID(s) based on the business agreement. If the AF does not provide MBS FSA ID(s), the MB-SMF determines MBS FSA ID(s) based on configured mapping from MBS service area and/or broadcast MBS session information (e.g. application ID) to MBS FSA ID(s) and sends the determined MBS FSA ID(s), to the AF (optionally via NEF). The MBS FSA ID(s) of a broadcast MBS session are communicated in the service announcement towards the UE. The UE compares those MBS FSA IDs(s) with the MBS FSA ID(s) in SIBs for frequency selection. During MBS Session Start for Broadcast in clause 7.3.1 and MBS Session Update for Broadcast in clause 7.3.3, the MB-SMF may include the MBS FSA ID(s) for the MBS session and send them to the NG-RAN nodes via the AMF. The NG-RAN nodes may then use those MBS FSA ID(s) to determine cells/frequencies within the MBS service area to broadcast MBS session data. For details, see TS 38.300 and TS 38.413.

In the case of network sharing, an Associated Session ID may be used as specified in clause 6.18. When the AF creates multiple broadcast MBS Sessions via different CNs to deliver the same content, it may provide the Associated Session ID which enables the NG-RAN to identify the multiple MBS Sessions delivering the same content. Source Specific IP Multicast Address specified in clause 6.5.3 may be used as Associated Session ID.