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Content for  TS 23.247  Word version:  17.4.0

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7.3  MBS procedures for broadcast Sessionp. 85

7.3.1  MBS Session Start for Broadcastp. 86

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 (e.g. USD as defined in TS 26.346) for the UE to receive MBS service, or provisioned with the configuration of Broadcast MBS session on application level (service announcement; the configuration may for instance be performed using SIP signalling, or methods described in TS 26.346). If the needed configuration is pre-configured, the UE does not need to interact with network.
Reproduction of 3GPP TS 23.247, Fig. 7.3.1-1: MBS Session Establishment for Broadcast
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Step 0.
Based on OAM configuration, RAN nodes announce in SIBs over the radio interface information about the MBS FSA IDs and frequencies of neighbouring cells.
Step 1.
To establish broadcast MBS session, the AF performs TMGI allocation and MBS session creation as specified in clause 7.1.1.2 or clause 7.1.1.3. The MBS service type indicates to be broadcast service. 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.
Step 2.
The MB-SMF may use NRF to discover the AMF(s) supporting MBS based on the MBS service area and select the appropriate one(s). Then the MB-SMF sends the Namf_MBSBroadcast_ContextCreate (TMGI, N2 SM information ([LL SSM], 5G QoS Profile), MBS service area, [MBS FSA ID(s)]) messages to the selected AMF(s) in parallel if the service type is broadcast service. The MB-SMF may include a maximum response time in the request.
Step 3.
The AMF transfers the MBS Session Resource Setup Request message, which contains the N2 SM information in the received Namf_MBSBroadcast_ContextCreate Request to all NG-RANs which support MBS in the MBS service area. The AMF includes the MBS service area.
Step 4.
NG-RAN creates a Broadcast MBS Session Context and stores the TMGI and the QoS Profile in the MBS Session Context. The LL SSM are optional parameters and only provided by MB-SMF to NG-RAN if N3mb multicast transport is configured to be used in the 5GC. If MBS FSA ID(s) were received, the NG-RAN may use those MBS FSA ID(s)s to determine cells/frequencies within the MBS service area to broadcast MBS session data based on OAM configuration about the MBS FSA IDs and related frequencies.
Step 5.
If NG-RAN prefers to use N3mb multicast transport (and if LL SSM is available in NG-RAN), the NG-RAN joins the multicast group (i.e. LL SSM).
If NG-RAN prefers to use N3mb unicast transport (or if the LL SSM is not available in NG-RAN) between the NG-RAN and MB-UPF, NG-RAN provides its N3mb DL Tunnel Info.
Step 6.
The NG-RAN reports successful establishment of the MBS Session resources (which may include multiple MBS QoS Flows) by sending MBS Session Resource Setup Response (TMGI, N2 SM information ([N3mb DL Tunnel Info])) message(s) to the AMF. N3mb DL Tunnel Info is only available when unicast transport applies between MB-UPF and NG-RAN. For more details, refer to TS 38.413.
Step 7.
The AMF transfers the Namf_MBSBroadcast_ContextCreate Response () to the MB-SMF. The AMF should respond success when it receives the first success response from the NG-RAN(s). And if all NG-RAN(s) report failure, the AMF should respond failure. The MB-SMF stores the AMF(s) which responds success in the MBS Session Context as the downstream nodes. If the AMF receives the NG-RAN response(s) from all involved NG-RAN(s), the AMF should include an indication of completion of the operation in all NG-RANs.
Step 8.
If N3mb unicast transport is to be used (i.e. N3mb DL Tunnel Info is present in the Namf_MBSBroadcast_ContextCreate Response message from AMF), the MB-SMF sends an N4mb Session Modification Request to the MB-UPF to allocate the N3mb unicast transport tunnel for a replicated MBS stream for the MBS Session. Otherwise, step 8 can be skipped.
Step 9.
NG-RAN broadcasts the TMGI representing the MBS service over radio interface. Step 9 can take place in parallel with step 6.
Step 10.
Another NG-RAN may report successful establishment of the MBS Session resources (which may include multiple MBS QoS Flows) by sending MBS Session Resource Setup Response (TMGI, N2 SM information ([N3mb DL Tunnel Info])) message after the AMF transferred the Namf_MBSBroadcast_ContextCreate Response () to the MB-SMF.
Step 11.
The AMF transfers the Namf_MBSBroadcast_ContextStatusNotify request () to the MB-SMF. When the AMF receives the response from all NG-RAN nodes, the AMF includes an indication of the completion of the operation. If the AMF does not receive responses from all NG-RAN nodes before the maximum response time elapses since the reception of the Namf_MBSBroadcast_ContextCreate Request, then the AMF should transfer the Namf_MBSBroadcast_ContextStatusNotify request () which indicates partial success or failure.
Step 12.
If N3mb unicast transport is to be used (i.e. N3mb DL Tunnel Info is present in the MBS Session Start Response message from AMF), the MB-SMF sends an N4mb Session Modification Request to the MB-UPF to allocate the N3mb unicast transport tunnel for a replicated MBS stream for the MBS Session. Otherwise, step 12 can be skipped.
Step 13.
The AF starts transmitting the DL media stream to MB-UPF using the N6mb Tunnel, or optionally un-tunnelled i.e. as an IP multicast stream using the HL MC address.
Step 14.
The MB-UPF transmits the media stream to NG-RAN via N3mb multicast transport or unicast transport.
Step 15.
The NG-RAN transmits the received DL media stream using DL PTM resources.
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7.3.2  MBS Session Release for Broadcastp. 88

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.
Reproduction of 3GPP TS 23.247, Fig. 7.3.2-1: MBS Session Release for Broadcast
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Step 1.
The AF/AS may stop the media stream before sending the MBS Session Release Request (TMGI) message to the 3GPP network.
Step 2.
The AF/AS performs MBS Session Deletion procedure to request release of MBS Session (steps 1 ~ 10 in Figure 7.1.1.4-1, or steps 1 ~ 13 in Figure 7.1.1.5-1).
Step 3.
MB-SMF sends Namf_MBSBroadcast_ContextRelease request (TMGI) to the AMF(s) that has been involved in the MBS Session.
Step 4.
The AMF sends an N2 message to all RAN nodes that have been involved to release MBS session. If a NG-RAN node receives multiple N2 message to release the MBS Session for the same TMGI (e.g. from several AMFs the NG-RAN is connected to), NG-RAN only performs step 5 and step 6 once.
Step 5.
The NG-RAN stops the PTM transmission.
Step 6.
If N3mb multicast transport has been used, the NG-RAN sends a Leave message (LL SSM) to stop the media stream to this NG-RAN node. If N3mb unicast transport has been used, the NG-RAN release its DL N3mb Tunnel Info. NG-RAN deletes its MBS Session Context.
Step 7.
The NG-RAN reports successful release of resources for the MBS Session by sending MBS Session Resource Release Response (TMGI) message(s) to the AMF(s).
Step 8.
The AMF sends Namf_MBSBroadcast_ContextRelease response (TMGI) to the MB-SMF.
Step 9.
The AF may start a TMGI de-allocation procedure (steps 11 ~ 14 in Figure 7.1.1.4-1, or steps 14 ~ 17 in Figure 7.1.1.5-1).
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7.3.3  MBS Session Update for Broadcastp. 88

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).
Reproduction of 3GPP TS 23.247, Fig. 7.3.3-1: MBS Session Update for Broadcast
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Step 1.
The AF starts MBS session update procedure by sending Nnef_MBSSession_Update Request to the NEF/MBSF with TMGI. The AF may adjust service requirement and/or broadcast area. The service requirements adjustment 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).
Step 2.
The MB-SMF sends Namf_MBSBroadcast_ContextUpdate Request (TMGI, N2 SM information (MBS Session ID, [MBS QoS profile], [service area(s)], [Area Session ID(s)], [MBS IP Multicast Tunnel Info(s)], [MBS FSA ID(s)]), [updated MBS service area]) to the AMFs. For a location dependent service, the MB-SMF may provide information about several location areas. If the broadcast area is updated, the MB-SMF may use NRF to discover the AMF(s) based on the new broadcast area and select the appropriate one(s). The MB-SMF may include a maximum response time in the request.
Depending on the change of the MBS service area, the MB-SMF may send Namf_MBSBroadcast_ContextCreate to some AMFs in the new MBS service area, Namf_MBSBroadcast_ContextRelease to some other AMFs in the old MBS service area.
Step 3.
The AMF sends MBS Session Resource Update to NG-RANs with TMGI, the updated 5G QoS Profile and the updated MBS service area.
Depending on the change of the MBS service area, the AMF may send MBS Session Resource Setup to some NG-RANs in new MBS service area (see clause 7.3.1) and MBS Session Resource Release to some other NG-RANs in old MBS service area.
Step 4.
The NG-RAN updates MBS Session Context.
Step 5.
The NG-RAN reports successful update of the MBS Session resources (which may include multiple MBS QoS Flows) by sending MBS Session Resource Update Response (TMGI, N2 SM information ([N3mb DL Tunnel Info])) message(s) to the AMF. N3mb DL Tunnel Info is only available when unicast transport applies between MB-UPF and NG-RAN and the NG-RAN wants the transport to be changed. The NG-RAN should be ready to receive using the N3mb DL tunnel. For more details, refer to TS 38.413.
Step 6.
The AMF sends Namf_MBSBroadcast_ContextUpdate Response to the MB-SMF. If the AMF received the NG-RAN responses from all involved NG-RAN(s), the AMF should include an indication of completion of the operation in all NG-RANs.
Step 6a.
If MBS service area is changed in such a manner that NG-RAN nodes are added or removed from handling the MBS session, and N3mb unicast transport is used, the MB-SMF sends an N4mb Session Modification Request to the MB-UPF to establish or release the N3mb unicast transport tunnel for establishing, or releasing the MBS stream for the MBS Session. Otherwise, step 6a can be skipped.
Step 7.
The NG-RAN updates the MBS Session. It takes place in parallel with step 5 to step 6.
Step 8.
Another NG-RAN may report successful update of the MBS Session resources (which may include multiple MBS QoS Flows) by sending MBS Session Resource Update Response (TMGI, N2 SM information ([N3mb DL Tunnel Info])) message after the AMF transferred the Namf_MBSBroadcast_ContextUpdate Response () to the MB-SMF. N3mb DL Tunnel Info is only available when unicast transport applies between MB-UPF and NG-RAN and the NG-RAN wants the transport to be changed. The NG-RAN should be ready to receive using the N3mb DL tunnel. For more details, refer to TS 38.413.
Step 9.
The AMF transfers the Namf_MBSBroadcast_ContextStatusNotify request () to the MB-SMF. When the AMF receives the response from all NG-RAN nodes, the AMF should include an indication of completion of the operation in all NG-RANs. If the AMF does not receive responses from all NG-RAN nodes before the maximum response time elapses since the reception of the Namf_MBSBroadcast_ContextUpdate Request, then the AMF should transfer the Namf_MBSBroadcast_ContextStatusNotify request () which indicates partial success or failure.
Step 10.
If MBS service area is changed in such a manner that NG-RAN nodes are added or removed from handling the MBS session, and N3mb unicast transport is used, the MB-SMF sends an N4mb Session Modification Request to the MB-UPF to establish or release the N3mb unicast transport tunnel for establishing, or releasing the MBS stream for the MBS Session. Otherwise, step 10 can be skipped.
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7.3.4  Support for Location dependent Broadcast Servicep. 90

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).
  • 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 clause 7.3.1 with the following additions:
  • 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.
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7.3.5  MBS Session Delivery Status Indication for Broadcastp. 90

The MBS Session Delivery Status Indication for broadcast is used by the MB-SMF to notify the AF/AS of conditions affecting the delivery of the MBS session (e.g. MBS session created, MBS session terminated, etc.). The occurrence of the indicated condition may have been detected at the MB-SMF or may have been reported to the MB-SMF by other entities involved in the MBS session delivery.
Reproduction of 3GPP TS 23.247, Fig. 7.3.5-1: MBS Session Delivery Status Indication for Broadcast
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Step 1.
The external AF subscribes event for delivery status towards the NEF, and the NEF subscribes corresponding event towards the MB-SMF (step 1a), or the legacy AS request status report towards the MBSF, and the MBSF subscribes event for delivery status towards the MB-SMF (step 1b), or the internal AF subscribes event for delivery status towards the MB-SMF (step 1c).
Step 2.
The MB-SMF notifies the TMGI and the event towards the NEF, and the NEF notifies the TMGI and corresponding event towards the external AF (step 2a), or the MB-SMF notifies the TMGI and the event towards the MBSF, and the MBSF sends Delivery Status Indication to legacy AS with the TMGI and the corresponding event (step 2b), or the MB-SMF notifies the TMGI and the event towards the internal AF (step 2c).
For the "MBS session started" event, after the MB-SMF contacts AMFs to request the establishment of the Broadcast MBS session, the MB-SMF may wait until it has received a Namf_MBSBroadcast_ContextCreate Response or Namf_MBSBroadcast_ContextStatusNotify with the indication of the completion of the operation from each AMF (see clause 7.3.1) before determining that the Broadcast MBS session has been started.
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7.3.6  Broadcast MBS Session Release Requirep. 91

When NG-RAN is not able continue to provide the Broadcast MBS Session, e.g. due to lack of radiou resources, NG-RAN may intitiate Broadcast Session Release Require procedure.
Reproduction of 3GPP TS 23.247, Fig. 7.3.6-1: Broadcast MBS Session Release Require
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Step 1.
If NG-RAN cannot continue to provide the Broadcast MBS session, e.g. due to lack of radio resources, the NG-RAN sends Broadcast Session Release Require (MBS Session ID) to the AMF.
Step 2.
The AMF initiates Broadcast Session Release towards the NG-RAN as defined in steps 4 - 7 in clause 7.3.2.
Step 3.
If unicast transport applies in N3mb, the AMF receives the DL tunnel Info for the Broadcast MBS Session from the NG-RAN in step 2. The AMF notifies the MB-SMF about the DL tunnel release via Namf_MBSBroadcast_ContextStatusNotify.
Step 4.
The MB-SMF performs N4mb Session Update to let MB-UPF stop the broadcast data forwarding towards the indicated DL tunnel and release the DL tunnel.
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7.4  MBS procedures for inter System Mobilityp. 92

7.4.1  Inter-system mobility with interworking at service layerp. 92

For inter-system mobility with interworking at service layer, i.e. the same multicast service is provided via eMBMS in E-UTRAN and MBS, the UE is instructed to switch between MBS and eMBMS:
  • Mobility from MBS to eMBMS.
    When moving to E-UTRAN/EPC, the UE initiates procedures as defined in TS 23.246 to receive MBMS service for the TMGI(s).
    If the UE has one or more unicast PDU Sessions (including, but not limited to, the PDU Session used for MBS and for another service (e.g. Public Safety service) with the QoS Flow(s) for the other service) moving to EPS, and if the handover procedure from 5GS to EPS using N26 interface described in clause 4.11.1.2.1 of TS 23.502 is used:
    • For the PDU Session used also for MBS, the SMF+PGW-C removes the UE from the Multicast MBS session context(s), if it exists, upon receiving a Modify Bearer Request of the PDU Session from the SGW (i.e. step 14a of clause 4.11.1.2.1 of TS 23.502).
    • The NG-RAN removes the UE from the Multicast MBS session context(s) if it exists, or removes the whole multicast session context if the UE is the last one for the Multicast MBS session (e.g. after receiving the UE Context Release Command message sent by the AMF).
    For 5GS to EPS Idle mode mobility with no N26, when the UE moves to the EPS and performs E-UTRAN/EPS attach according to step 8 of clause 4.11.2.4.1 of TS 23.502, if the UE does not maintain registration in 5GC, upon reachability time-out, the AMF may implicitly detach the UE and release the possible remaining PDU Session(s) in 5GC. The SMF/PGW-C removes the UE from the Multicast MBS session context(s), if it exists, upon receiving a tracking area update from the UE.
  • Mobility from eMBMS to MBS.
    When the UE has moved to NR/5GC, it triggers the multicast context and multicast flow setup/modification via PDU Session Modification procedures as defined in clause 6.8 to receive MBS transport for the TMGI(s).
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