Content for  TS 23.247  Word version:  18.7.0

For local multicast services, the MBS service area information is provided to the UE and the 5GC as specified in clauses 7.1.1.2 and 7.1.1.3 with the following differences and clarifications:

• For the Service Announcement, MBS service area information is included unless it is preconfigured.
• When performing the MBS session creation request to the 5GC, the MBS service area information for a Multicast MBS session is provided by the AF unless it is preconfigured.

For the case that the multicast service is only available within a limited area, the UEs outside the MBS service area are not allowed to join the multicast service. The Multicast MBS session join and session establishment for multicast service available within a limited area are performed as specified in clause 7.2.1.3 with the following differences and clarifications:

• The local Multicast MBS session has been created where the AF provided the MBS service area information as specified in clause 7.2.4.3.1.
• The UE may have information about local multicast service including MBS service area via Service Announcement as specified in clause 7.2.4.3.1.
• In step 1, if the UE determines that it is in the MBS service area based on the information about local multicast service e.g. obtained via Service Announcement, the UE sends the PDU Session Modification Request (MBS Session ID) or the PDU Session Establishment Request (MBS Session ID) as a Join Request to join the multicast group. If the UE determines that it is outside the MBS service area, the UE does not send the Join Request.
• In step 3, the SMF obtains the MBS service area (i.e. Cell ID list or TAI list) of the indicated MBS session from the MB-SMF, and the SMF determines the indicated MBS session corresponds to local multicast service based on the MBS service area.
• In step 5, the SMF checks whether the UE is inside or outside the MBS service area.
  • The SMF determines whether the UE is inside the MBS service area by comparing the User Location Information of the UE received from the AMF with the MBS service area received from the MB-SMF.
  • If the SMF detects that the UE is inside the MBS service area, the SMF continues the process of multicast session join as specified in clause 7.2.1.3 with the following additions:
  • The SMF sends the UE a PDU Session Modification Command or a PDU Session Establishment Accept indicating a Join Accept as a response to the Join Request. The Joint Accept includes the MBS service area (i.e. Cell ID list or TAI list).
  • The Multicast MBS session information sent by the SMF to the NG-RAN includes the MBS service area (i.e. Cell ID list or TAI list).
  • If the RAN node serving the UE does not support MBS the SMF applies individual delivery towards the UE. The SMF configures the UPF to send data related to the Multicast MBS session via individual delivery within a PDU session of the UE.
• If the SMF detects that the UE is outside the MBS service area, the SMF rejects the multicast session join, so sends a Join Reject to the UE indicating that the MBS join is rejected. The Joint Reject includes the reject reason (outside of local service area) and the MBS service area (i.e. Cell ID list or TAI list).
  In this case, the MBS Session establishment (i.e. resources establishment for MBS traffic delivery) for the UE is not performed.
• If the Join Request from the UE is accepted, the SMF subscribes to the UE mobility event notification from the AMF (e.g. UE moving into or out of Area Of Interest, which is set by MBS service area), by invoking Namf_EventExposure_Subscribe service operation as specified in clause 5.2.2.3.2 of TS 23.502. The SMF supplies the service area associated with the Multicast MBS session as Area Of Interest.
• For the UE that received the Join Reject from the SMF, later, if the UE detects that it is inside the MBS service area based on the MBS service area provided in the Join Reject, the UE sends the PDU Session Modification Request (MBS Session ID) to join the multicast group.

The Handover procedure for the UE is performed as defined in clause 7.2.3 with the following additions:

• If the UE is camping at the Source RAN node and receiving multicast data corresponding to the MBS Session ID via the 5GC Shared MBS traffic delivery before the Handover, for Xn based handover in clause 7.2.3.2, the Source RAN node includes MBS Session ID and MBS service area to the Target RAN node during Handover Preparation phase. For N2 based handover in clause 7.2.3.3, this step corresponds to Handover Request and Handover Required message, respectively.
• If the UE is camping at the Source RAN node and receiving multicast data corresponding to the MBS Session ID via the 5GC individual MBS traffic delivery before the Handover, for the N2 Handover in clause 7.2.3.4, the SMF includes MBS session area information (MBS Session ID and MBS service area) in N2 SM information to the Target RAN node in Handover request.
• If the Target RAN node support MBS, it determines whether to establish the resources for multicast distribution and data forwarding for MBS Session ID, based on the received MBS Session ID provided by the source RAN (if source RAN support MBS) or SMF (if source RAN not support MBS), and target location of the UE. If UE is not in the in the MBS service area provided by the source RAN (if source RAN support MBS) or SMF (if source RAN not support MBS), the Target RAN does not allocate RAN resources, including the resource for data forwarding, for the multicast MBS Session to the UE.
• If the target RAN node support MBS, when it determines that the UE is in the MBS service area and that the shared delivery is not established for the multicast session ID, the target NG-RAN initiates the shared delivery establishment as specified in clause 7.2.1.4.
• When the AMF receives the User Location Information from target RAN node via the Path Switch Request message or Handover Notify message, the AMF provide it to the SMF. When the SMF get the User Location Information, the SMF check the MBS service area of UE camping cell by comparing the User Location Information received from AMF with the MBS service area received from the MB-SMF. The SMF uses the determined UE location and MBS service area as follows:
  • The SMF determines whether the UE is outside the MBS service area by comparing the received Cell ID and tracking area ID with the MBS service area received from the MB-SMF.
  • If the UE is inside the MBS service area and target RAN node does not support MBS, the SMF applies individual delivery towards the UE. If associated QoS flows are not yet included in the PDU session, the SMF updates the PDU session with associated QoS flows. If the SMF did not configure the UPF to receive the MBS data packet from the tunnel associated with the Multicast MBS session before, the SMF informs the MB-SMF of the MBS session and UPF DL N19mb Tunnel information. MB-SMF configure the MB-UPF to transmit the Multicast MBS session data towards UPF using the received downlink tunnel ID.
• If the UE is out of the service area of the MBS session:
  • If the target NG-RAN node does not support MBS, the SMF deletes the associated QoS flow from NG-RAN node and the UPF after the completion of the handover procedure.
  • Per operator's policy (e.g. when a local configured timer expires since the UE left the whole MBS service area of the MBS session) the SMF may remove the UE from the MBS session as defined in clause 7.2.2.3. When the UE is removed from the local MBS session, the SMF also unsubscribes to the AMF from the notifications about the "UE moving in or out of a subscribed "Area Of Interest"" event.

For the local MBS session activation, the differences comparing to the procedure defined in clause 7.2.5.2 are as below.

• The SMF invokes Namf_MT_EnableGroupReachability service operation to AMF, which include the MBS service area associated with the MBS session.
• For the UE in CM-IDLE state, when the AMF triggers the paging, it takes the received MBS service area information into account and only triggers the paging at the NG-RAN nodes which are included in the MBS service area.
• SMF checks whether the UE is in or out of the MBS service area based on the change notification or UE location information included in Nsmf_PDUSession_UpdateSMContext Request or Namf_MT_UEReachabilityInfoNotify message. Based on that information, the SMF determines how to activate the MBS session same as the handling when the SMF get the User Location Information defined in clause 7.2.4.3.3.
• When the SMF provides the MBS session information to the NG-RAN nodes, it includes the MBS service area in the N2 SM information.

When the SMF receives a notification about a UE location change or is becoming aware of a UE location change (e.g. during handover, Mobility Registration Update and Service Request procedures), the SMF checks whether the new UE location is inside or outside the MBS service area of the MBS session.

• For the case UE is out of the MBS service area of the MBS session:
  • If RAN node does not support MBS, the SMF delete the associated QoS flow from the RAN node and the UPF.
  • Per operator's policy (e.g. when a local configured timer expires since the UE left the MBS service area of the MBS session) the SMF may remove the UE from the multicast MBS session as defined in clause 7.2.2.3. When the UE is removed from the local MBS session, the SMF also unsubscribes to the AMF from the notifications about the "UE moving in or out of a subscribed "Area Of Interest"" event.
• For the case UE comes back to the MBS service area of the multicast MBS session after moving out of the MBS service area of the multicast MBS session, e.g. before the local configured timer expires:
  • If the UE is still in the multicast MBS session and the multicast MBS session is in Active state, the SMF tries to activate the multicast MBS session towards the UE.

If UE mobility can happen within the same NG-RAN between cells in or out of the service area,

• The NG-RAN detects whether the UE is IN or OUT of an MBS service area and notifies the SMF if the UE moves in or out of the MBS service area.
• When the SMF knows the UE is IN or OUT of an MBS service, the SMF behaves as in clause 7.2.4.3.5.

The Connection Resume procedure for the UE is performed as defined in clause 7.2.3.7 with the following additions:

• The source RAN, if supporting MBS and if the MBS session is active, provides MBS service area to the target RAN during the UE Context Retrieval procedure;
• An MBS supporting target RAN then applies the procedures in clause 7.2.4.3.6.
• The SMF applies the procedures in clause 7.2.4.3.5.