Content for  TS 23.247  Word version:  18.4.0

For location dependent MBS, the MBS session creation procedure is performed as defined in clause 7.1.1.2 with the following additions and difference:

• Multiple AFs may start the same Multicast MBS session with different content in different MBS service areas. The AF (or NEF/MBSF if involved) selects MB-SMF for different MBS service areas.
• For each MBS service area, the AF creates a location dependent component of an MBS session for that service area towards the MB-SMF and provides the service area, which may be via NEF or MBSF. The MB-SMF additionally returns the Area Session ID allocated by MB-SMF in the response to a request to create a location dependent component of a Multicast MBS session, and the NEF forwards this Area Session ID to the AF. The AF provides the Area Session ID in subsequent requests related to that location dependent component of the MBS session.
• When requesting the creation of a location dependent component of the MBS session for a service area, the AF provides an indication that the request is for the creation of a location dependent component of the MBS session.
• The NEF, if involved in the MBS Session, maps MBS service areas of external format (if any) to network internal format (list of cells, TAIs).
• MB-SMF allocates Area Session ID, and updates its NF profile towards the NRF with the MBS Session ID, MBS service area and Area Session ID.
• The QoS of Multicast MBS session is determined based on the service requirements per MBS Session. MB-SMF assign the same QFI for MBS QoS Flow with the same QoS requirement in different MBS service areas.
• The MB-SMF configures the MB-UPF separately for each service area. The MB-SMF may select the MB-UPF based on the MBS service area.
• All MBS service area(s) of the location dependent MBS session are indicated to the UE in the Service Announcement as defined in clause 6.11.
• The AF transmits the DL media streams to MB-UPF via tunnels to differentiate the content delivered to different areas.

The location dependent multicast session join and establishment procedure is performed as defined in clause 7.2.1 with the following additions:

• The location dependent Multicast MBS session is created as described in clause 7.2.4.2.0.
• The UE may have information about the location dependent multicast service including all MBS service areas of the location dependent MBS session via Service Announcement as specified in clause 7.2.4.3.1.
• If the UE determines that it is in MBS service area of the location dependent MBS session based on the information about local multicast service e.g. obtained via Service Announcement, the UE sends Join Request to join the multicast group. If the UE determines that it is outside all MBS service area of the location dependent MBS session, the UE does not send the Join Request.
• If SMF requires information about the multicast MBS Session Context for the indicated MBS Session ID, the SMF requests MB-SMF information via Nnrf_NFDiscovery_Request Request (MBS Session ID, UE location). The SMF should provide the TAI where the UE is located as input for the MB-SMF discovery. If the NRF does not have information about service areas for an MBS Session ID in the MB-SMF profile but obtains a TAI in combination with MBS Session ID as query parameter, the NRF ignores the TAI and provides the MB-SMF profile matching the MBS Session ID.If the TAI is not included, but the related MB-SMF include the service area, the NRF return all the MB-SMF associated with that MBS Session ID.
• The NRF provides information about the MB-SMF(s) serving the Multicast MBS session at the possible indicated location. The NRF provides the service areas and Area Session IDs for the Multicast MBS session as part of the MB-SMF profile(s), via Nnrf_NFDiscovery_Request Response (MB-SMF profile (Area Session ID(s), MBS service area(s)). The SMF selects the MB-SMF based on the location area where the UE is residing (if the TAI is not provided to the NRF) and interacts with MB-SMF to retrieve QoS information of the multicast QoS flow(s) for the MBS Session ID and subscribes to notifications about the MBS Session ID.
• The SMF check whether the UE is inside MBS service areas of the location dependent MBS session by comparing the User Location Information of the UE provided by the AMF with the MBS service areas received from the NRF. If the UE is out of all MBS service area of the location dependent MBS session, the SMF reject the multicast session join request.
• If the Join Request from the UE is accepted, the SMF may subscribe at the AMF using the Namf_EventExposure service to notifications about the "UE moving in or out of a subscribed "Area Of Interest"" event. The SMF supplies all MBS service areas of the location dependent MBS session as Area Of Interest.
• The SMF requests the AMF to transfer an N2 message to the RAN node using the Nsmf_PDUSession_UpdateSMContext response, to provide the NG-RAN with Multicast MBS session information which additionally includes the Area Session ID.
• If the NG-RAN node supports MBS, the NG-RAN uses the received MBS Session ID and Area Session ID to determine the local Multicast MBS session context and whether the user plane for the local Multicast MBS session is already established. If the RAN determines the shared delivery is not established for the MBS Session ID and Area Session ID, the NG-RAN initiates the shared delivery establishment as specified in clause 7.2.1.4 and provides the Area Session ID, tracking area ID(s) concerning the RAN node in addition to MBS Session ID in the request for shared delivery establishment. The MB-SMF provides MBS service area information (Area Session ID(s), MBS service area(s)) associated with the same MBS session to NG-RAN in the shared delivery establishment response. MB-SMF may either provide only the service areas concerning the target RAN node or all service areas associated with the MBS session. If the MB-SMF only provides the service areas concerning the target RAN node, which includes the cell ID(s), the cell ID is included if the tracking area IDs associated with the indicated cell ID is received by the MB-SMF.
• If the NG-RAN node serving the UE does not support MBS and the UE is in the MBS service area, the SMF apply individual delivery towards the UE. The SMF configures the UPF to send data related to the Multicast MBS session and service area via individual delivery within a PDU session of the UE. The SMF additionally subscribes at the AMF using the Namf_EventExposure service to notifications about UE location changes (e.g. for a small MBS service area), or to notifications about the "UE moving in or out of a subscribed "Area Of Interest"" event. In the latter case, the SMF supplies the service area associated with the multicast area session where the UE resides as Area Of Interest. The SMF configures separate ingress terminations at the UPF for each service area and interacts separately for each service area (providing MBS Session ID and Area Session ID) with the MB-SMF to request or terminate the distribution of data for the MBS session and service area towards the UPF.

The Handover procedure for the UE is performed as defined in clause 7.2.3.2, 7.2.3.3, and 7.2.3.4 with the following additions:

• If the UE is receiving multicast data corresponding to the MBS Session ID and Area Session ID via the 5GC Shared MBS traffic delivery from cells served by the Source NG-RAN before the handover, for the Xn Handover (comparing with the clause 7.2.3.2), the following applies:
  • The Source RAN node includes MBS Session ID, Area Session ID and MBS service area associated with the cell where the UE resides to the Target RAN node.
• If the UE is receiving multicast data corresponding to the MBS Session ID and Area Session ID from cells served by the Source NG-RAN via the 5GC Shared MBS traffic delivery before the handover, for the N2 Handover (comparing with the clause 7.2.3.3), the following applies:
  • The source RAN node includes MBS session area information (MBS Session ID, Area Session ID and MBS service area associated with the cell where the UE resides) for delivery to the Target RAN node within the Source to Target transparent container in the Handover Required message.
  • The SMF forwards the Source to Target transparent container and may also include MBS session area information (MBS Session ID, Area Session ID and MBS service area) to the Target RAN in Handover request.
• If the UE is receiving multicast data corresponding to the MBS Session ID and Area Session ID from cells served by the Source NG-RAN via the 5GC Individual MBS traffic delivery before the Handover, for the Xn/N2 handover procedure (comparing with the clause 7.2.3.4), the following applies:
  • For the N2 handover procedure, the SMF includes MBS session area information (MBS Session ID, Area Session ID, and MBS service area) associated with the last known service area of the UE in N2 SM information to the Target RAN node in Handover Request message.
• If the target RAN node supports MBS, it determines whether to establish the resources for multicast distribution and data forwarding for the received MBS Session ID and Area Session ID, based on MBS Session ID, Area Session ID, MBS service area provided by the source RAN (if source RAN support MBS) or SMF (if source RAN not support MBS) and the target location of the UE. If UE is not in the MBS service area provided by the source RAN (if source RAN supports MBS) or SMF (if source RAN does 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 the shared delivery is not established for the multicast session ID and Area Session ID, the target NG-RAN initiates the shared delivery establishment as specified in clause 7.2.1.4 and provides the Area Session ID and tracking area ID(s) concerning the RAN node in addition to MBS Session ID in the request for shared delivery establishment. The MB-SMF provides MBS session area information (Area Session ID(s), MBS service area(s)) associated with the MBS session to the NG-RAN in the shared delivery establishment reply. The MB-SMF may either provide only the service areas concerning the target RAN node or all service areas associated with the MBS session.
• If the target RAN supports MBS, but the Source RAN does not support MBS, the SMF configures the UPF to stop sending data related to the Multicast MBS session and service area via the associated PDU session of the UE. The SMF unsubscribes at the AMF using the Namf_EventExposure service to notifications about UE location changes, or to notifications about the "UE moving in or out of a subscribed "Area Of Interest"" event (for an individual service area).
• 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 determines the MBS service area of the UE camping cell by comparing the User Location Information received from AMF with the MBS service areas received from the NRF. The SMF uses the determined MBS service area and determined user location as follows:
  • The SMF updates the Area Session ID in the locally stored the UE MBS Session Context with the corresponding Area Session ID if the Area Session ID is changed.
  • If the target RAN does not support MBS, the Source RAN supported MBS, and the UE is in a service area of the MBS session, the SMF applies individual delivery towards the UE. The SMF configures the UPF to send data related to the Multicast MBS session and service area via the associated PDU session of the UE. The SMF additionally subscribes at the AMF using the Namf_EventExposure service to notifications about UE location changes, or to notifications about the "UE moving in or out of a subscribed "Area Of Interest"" event. In the latter case the SMF supplies the service area of the multicast area session as Area Of Interest. If associated QoS flows are not yet included in the PDU session, the SMF updates the PDU session with associated QoS flows.
  • If the UE has moved to another MBS service area of the MBS session:
    • If the target NG-RAN node supports MBS after the completion of the handover procedure, the SMF provides the MBS session related information including the new Area session ID to NG-RAN via the PDU Session Modification procedure. Per the received the MBS session related information, the 5GC shared delivery is established.
    • If the target NG-RAN node does not support MBS, the SMF updates the UPF to forward the MBS data packets which are received from the tunnel associated with the new Area Session ID to the target NG-RAN node. If the SMF did not configure the UPF to receive the MBS data packet from the tunnel associated with the new Area Session ID before, the SMF informs the MB-SMF of the new Area Session ID 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 SMF subscribed to the "Area Of Interest" event, the SMF also updates the subscription with the new service area as "Area Of Interest".
  • If the UE has moved out of all the MBS service areas of the MBS session:
    • If the target NG-RAN node does not support MBS, the SMF deletes the associated QoS flow from NG-RAN and UPF after the completion of the handover.
    • Per operator's policy (e.g. when a local configured timer expires since the UE left the whole MBS service area), 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 location dependent 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.

When the location dependent MBS session is activated, the MBS session is activated in the whole MBS service area of the MBS session. It is not supported that the same MBS session is in Active state in one MBS service area but in Inactive state in another MBS service area. When the MB-SMF is requested by an AF to activate the MBS session in a service area of the MBS session or the MB-UPF reports detection of data for a service area of the MBS session, the MB-SMF triggers the activation for all service areas of the MBS session that it serves, i.e. whole MBS session is activated. For the location dependent 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 includes the whole MBS service area associated with the MBS session, i.e. the sum of all MBS service area associated with the MBS Session ID regardless of the Area Session ID.
• For the UE in CM-IDLE state, when the AMF triggers the paging, it take the receiving MBS service area information into account. Only the NG-RAN nodes which are included in the MBS service area need to be triggered for paging.
• 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 in the same way as the handling defined in clause 7.2.4.2.3
• When the SMF provides the MBS session information to the NG-RAN nodes, it includes the MBS service area, and Area Session ID, in the N2 SM information.

If UE has moved out of the MBS service area corresponding to the original Area Session ID, the SMF checks whether UE is in MBS service area corresponding to a new Area Session ID within the same MBS session:

• For the case UE is out of the original MBS service area but in another MBS service area of the MBS session:
  • If the RAN node does not support MBS and the MBS session is active, the SMF updates the UPF to forward the MBS data packets which are received from the tunnel associated with the new Area Session ID to the RAN node. If the SMF did not configure the UPF receiving the MBS data packet from the tunnel associated with the new Area Session ID before, the SMF informs the MB-SMF of the new Area Session ID and UPF DL N19mb Tunnel information. The MB-SMF configure the MB-UPF to transmit the Multicast MBS session data towards UPF using the received downlink tunnel ID.
  • The SMF updates the AMF of the area of interest event subscription by supplying the new MBS service area as Area Of Interest.
• For the case UE is out of all the MBS service areas of the MBS session:
  • If RAN node does not support MBS, the SMF delete the associated QoS flow from NG-RAN and UPF.
  • Per operator's policy (e.g. when a local configured timer expires since the UE left the whole MBS service area), 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 location dependent 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 whole 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, the SMF adds the associated QoS flow at NG-RAN and UPF.

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 all MBS service areas of the location dependent MBS session:

• For the case that UE is out of all MBS service area of the location dependent 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 whole 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. 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 MBS service area of the location dependent MBS session after moving out of the whole 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.

When the UE moves from one service area to another served by the same NG-RAN, the NG-RAN node that supports MBS handles content switching due to mobility between service areas it serves without interaction with SMF. If it is the first that UE enters a new location area the RAN node requests shared delivery from the MB-SMF for the corresponding Area Session ID. If the last UE leaves a location area the RAN node requests the termination of shared delivery from the MB-SMF for the corresponding Area Session ID. UE mobility can happen within the same NG-RAN between cells in or out of all the MBS service areas:

• The NG-RAN detects whether the UE is IN or OUT of all MBS service areas of a location dependent MBS session. If the UE moves in or out of all MBS service areas of a location dependent MBS session, the NG-RAN notifies the SMF.
• When the SMF knows the UE is IN or OUT of all MBS service area of location dependent MBS session, the SMF behaves as in clause 7.2.4.2.6.

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

• For an MBS-supporting target NG RAN
  • The target RAN node obtains MBS session information including an area session ID from the source RAN node (during the connection retrieval) or the SMF and initiates the shared delivery establishment (if not established yet) as specified in clause 7.2.1.4 providing that area session ID. It obtains information about location areas and related area session IDs during the shared delivery establishment. The target RAN then applies the procedures in clause 7.2.4.2.7.
• For a non MBS-supporting target NG RAN, the SMF subscribes at the AMF using the Namf_EventExposure service to notifications about UE location changes (if not yet done), and applies the procedures in clause 7.2.4.2.5.