Content for  TS 23.247  Word version:  18.4.0

The Broadcast MBS Session Start follows the common procedure specified in clause 7.1.1.2 or clause 7.1.1.3, which consist of TMGI Allocation and MBS Session Create. It is possible for AF to allocate TMGI once but create the MBS Session for multiple times. A combined procedure to perform both TMGI allocation and MBS Session Create is available. The TMGI Allocation is used by AF to obtain the TMGI as MBS Session ID (i.e. TMGI) and perform service announcement towards UEs. The MBS Session Create (with MBS service type set to broadcast service) is used by the AF to indicate the impending start of the transmission of MBS data, and to provide the session attributes, so that resources for the MBS Session are set up in the MB-UPF and in the NG-RAN for 5GC Shared MBS traffic delivery. The MBS Session Create can be used if TMGI has not been allocated. In this case, MB-SMF will allocate a unique TMGI for the AF and then start the MBS Session. To receive the data of broadcast communication service, the UE is either preconfigured with needed configuration (see TS 24.575 for UE pre-configuration) for the UE to receive MBS service, or provisioned with the configuration of Broadcast MBS session on application level (service announcement as described in TS 26.502 and TS 26.517). If the needed configuration is pre-configured, the UE does not need to interact with network.

Depending on the NG-RAN's preference to use multicast or unicast transport over N3mb and the availability of the LL SSM, step 5a or step 5b is executed.

To support resource sharing across multiple broadcast MBS Sessions during network sharing (see clause 6.18), in addition to clause 7.3.1, the following enhancement applies:

• Step 2: The MB-SMF includes Associated Session ID in the N2 SM information in Namf_MBSBroadcast_ContextCreate.
• Step 4: A shared NG-RAN node identifies the associated MBS sessions as specified in clause 6.18. The associated MBS sessions share radio resource configuration based on the existing Broadcast MBS Session context.
• Step 5a: If the NG-RAN determines there is already an existing broadcast MBS session delivering the same content, the NG-RAN may skip joining the multicast group based on operator policy, i.e. step 5a can be skipped.
• Step 5b: If the NG-RAN determines there is already an existing broadcast MBS session delivering the same content, a shared NG-RAN node may decide not to allocate N3mb DL tunnel endpoint.
• Step 6:
  • For N3mb multicast transport, when the NG-RAN node decides to skip joining the multicast group in step 5a, the NG-RAN still reports successful establishment of the MBS Session resource.
  • For N3mb unicast transport, when the NG-RAN decides not to allocate N3mb DL Tunnel endpoint in step 5b, the NG-RAN still reports successful establishment of the MBS Session resource but the N3mb DL Tunnel Info is not included in MBS Session Resource Setup Response.
• Step 8: If the N3mb unicast transport is used but N3mb DL Tunnel Info is not present in MBS Session Resource Setup Response, the MB-SMF accepts the response and skips step 8.
• Step 9: If the NG-RAN determines that radio resource has been allocated for another broadcast MBS Session delivering the same content as specified in clause 6.18, the NG-RAN advertises the TMGI of the broadcast MBS session, and reuses such already allocated radio resource for the MBS data transmission for the broadcast MBS session.
• Step 10 ~ step 12: The handling is the same as steps 5, 6, 7 and 8.
• Step 14: If the user plane of a broadcast MBS session from its MB-UPF to the shared NG-RAN is not established, the NG-RAN will not receive the MBS packets from the MB-UPF.
• Step 15: If the NG-RAN receives multiple DL media streams for the same content represented by the same Associated Session ID via multiple CNs, the NG-RAN should deliver only one DL media stream.

The MBS Session Release for broadcast follows the MBS Session Deletion (e.g. TMGI De-allocation and MBS Session Deletion) so that resource for shared MBS delivery is released. It is possible for AF to stop MBS Session but keep TMGI allocated.

Depending on whether multicast or unicast transport is used over N3mb, step 6a or step 6b is executed.

To support resource sharing across multiple broadcast MBS Sessions, in addition to clause 7.3.2, the following enhancement applies:

• Step 5:
  • If the NG-RAN determines there are other associated broadcast MBS Sessions based on the Associated Session Identifier, the step 5 is skipped.
• Step 6a:
  • If the NG-RAN skipped joining the multicast group (LL SSM) in clause 7.3.1a, the NG-RAN does not send a Leave message (LL SSM),
  • Otherwise, if the NG-RAN joined the multicast group (LL SSM) previously, and if the NG-RAN determines there are other associated broadcast MBS Sessions based on the Associated Session Identifier, the NG-RAN may trigger procedure of Transport change for resource sharing across broadcast MBS Sessions during network sharing as specified in clause 7.3.7.
• Step 6b:
  • If the DL N3mb Tunnel for the broadcast MBS Session was not allocated previously in clause 7.3.1a, step 6b is skipped.
  • Otherwise, if the DL N3mb Tunnel for the broadcast MBS Session was allocated previously, and if the NG-RAN determines there are other associated broadcast MBS Sessions based on the Associated Session Identifier, the NG-RAN may trigger the procedure of Transport change for resource sharing across broadcast MBS Sessions during network sharing as specified in clause 7.3.7.

The MBS Session Update for broadcast is used by the AF to update the broadcast area or service requirements of the MBS Session which may lead to addition of new MBS QoS Flow(s), removal of existing MBS QoS Flow(s) or update of existing MBS QoS Flow(s).

The clause describes procedures to support the Location dependent broadcast service as described in clause 6.2. The MBS session creation procedure is performed as defined in clause 7.1.1.2 with the following additions:

• Multiple AFs may start the same Broadcast MBS session with different content in different MBS service areas. The NEF selects MB-SMF as ingress control node(s) for different MBS service areas.
• If presented, the NEF maps possible external identifiers for MBS service areas to network-internal identifiers (e.g. list of cells, TAIs).
• An NEF/MBSF uses the service area to discover the MB-SMF.
  If different MB-SMFs are assigned for different MBS service areas belonging to different MB-SMF service areas for an MBS session as specified in clause 6.2.3, an MB-SMF shall accept TMGIs allocated by other MB-SMF.
• For Location dependent Broadcast Service, MB-SMF allocates Area Session ID, and updates its NF profile towards the NRF with the TMGI and Area Session ID.
• The MB-SMF may select the MB-UPF based on the MBS service area.
• The MBS service area(s) are indicated to the UE in the Service Announcement as defined in clause 6.11.

The MBS session establishment procedure is performed as defined in clauses 7.3.1 and 7.3.1a with the following additions or clarification:

• MB-SMF requests the AMF to transfer an N2 message (i.e. MBS Session Resource Setup Request) to the NG-RAN nodes of the MBS service area with Broadcast MBS session information which additionally includes the Area Session IDs and MBS service areas.
• The NG-RAN uses the received MBS Session ID and Area Session IDs to determine the local Broadcast MBS session contexts.
• The NG-RAN responds for service areas it handles with the Area Session ID(s) and DL tunnel endpoint(s) for the DL tunnel(s) from MB-SMF if unicast transport applies over N3mb between MB-UPF and NG-RAN.
• According to the Area Session ID(s) and DL tunnel endpoint(s) provided by NG-RAN, the MB-SMF instructs the MB-UPF to send location dependent content.
• The AF transmits the DL media streams to MB-UPF via tunnels to differentiate the content delivered to different areas.