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Content for  TS 23.247  Word version:  18.7.0

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7.2.5 MBS session activation and deactivation  7.2.5.1 General  7.2.5.2 MBS session activation procedure  7.2.5.3 MBS session deactivation procedure 
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7.2.5  MBS session activation and deactivation  p. 88

7.2.5.1  General  p. 88

MBS Session activation procedure is for multicast only. MBS Session activation procedure is triggered by MB-SMF, when it receives the notification from MB-UPF for the downlink MBS DL data, or when it receives the request directly from AF or via NEF. The MBS Session activation procedure is used for activating the resources for MBS data at NG-RAN node. The multicast session state transits from Inactive to Active after MBS Session activation procedure, see clause 4.3.
MBS Session deactivation procedure is for multicast only. MBS Session deactivation procedure is triggered by MB-SMF, when it receives the notification from MB-UPF in the case that there is no downlink data to be transmitted for some duration, or when it receives the request directly from AF or via NEF. The MBS Session deactivation procedure is used for deactivating the resources for MBS data at NG-RAN node. The multicast session state transits from Active to Inactive after MBS Session deactivation procedure, see clause 4.3.
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7.2.5.2  MBS session activation procedure  p. 89

The following can trigger the MBS session activation procedure:
  • AF requests MB-SMF to activate the MBS session;
  • MB-UPF receives the multicast data and notifies MB-SMF.
Reproduction of 3GPP TS 23.247, Fig. 7.2.5.2-1: MBS session activation procedure
Figure 7.2.5.2-1: MBS session activation procedure
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In this procedure, steps 11 to 15 are executed if the MB-SMF finds out there are shared tunnel established. Steps 11 to 15, if needed, are executed in parallel with steps 2 to 10.
Step 1.
The procedure may be triggered by the following events:
  • When the MB-UPF receives downlink data for a multicast MBS session, based on the instruction from the MB-SMF (as described in clause 7.2.5.3), the MB-UPF sends N4mb Notification (N4 Session ID) to the MB-SMF for indicating the arrival of DL MBS data.
  • The AF sends MBS Activation request (TMGI) to the MB-SMF directly or via NEF.
Step 2.
MB-SMF sends Nmbsmf_MBSSession_ContextStatusNotify (MBS Session ID, multicast session state = Active) to SMF(s).
The SMF sets the related multicast MBS session state to Active and finds out the list of UEs that joined the multicast MBS session identified by the related TMGI. If the SMF determines the user plane of the associated PDU session(s) of the UE(s) with respect to the TMGI are activated already, steps 3-8a will be skipped for those UE(s), i.e. executed from step 8b.
Step 3.
The SMF invokes Namf_MT_EnableGroupReachability Request (List of UEs, [PDU Session ID of the associated PDU Sessions], TMGI, [UE reachability Notification Address], [most demanding ARP, 5QI of all MBS QoS Flow within MBS session], [MBS service area]) to AMF(s). When later UE is reachable, the UE reachability Notification Address is used by the AMF to identify and notify the related SMF.
After receiving the request, for each UE in the list, the AMF determines CM state of the UE: see steps 4 - 7.
Step 4a.
If there are UEs involved in the multicast MBS Session and in CM-CONNECTED state, the AMF indicates those UEs to the SMF, using Namf_MT_EnableGroupReachability Response (UE list). Otherwise, the response does not include UE list.
Step 4b.
For each UE in the UE list included in step 4a, if the QoS profile(s) for associated PDU Session has not yet been provided, the SMF invokes Namf_Communication_N1N2MessageTransfer (N2 SM information (PDU Session ID, MBS Session ID, [QoS profile(s) for associated QoS flow(s)], [mapping information between the unicast QoS flow and multicast QoS flow])) to the AMF for the UE which is identified in step 4a. The associated unicast QoS Flow(s) as well as the mapping information between the unicast QoS Flow(s) and multicast QoS Flow(s) are included to support the 5GC Individual MBS traffic delivery. The SMF may also include the MBS assistance information for the MBS session in N2 SM Information, if the MBS subscription data from the UDM contains the MBS assistance information which includes the ID(s) of the MBS session(s) that the UE joined. The MBS assistance information for MBS session sent to the NG-RAN is described in clause 6.17.
The procedure continues at step 9.
Step 5.
[Conditional] If AMF determines that there are UEs in CM-IDLE state and involved in the multicast MBS Session, the AMF figures out the paging area covering all the registration areas of those UE(s), which need to be paged. The paging area needs to be further restricted to be within the MBS service area if received in step 3. The AMF may apply paging differentiation as specified in clause 6.12. The AMF sends a Multicast Group paging request message to the NG-RAN node(s) belonging to this Multicast Paging Area with the involved UE list and TMGI as the identifier to be paged if the related NG-RAN node(s) support MBS. If the AMF knows that the NG-RAN node(s) do not support MBS based on configuration, the AMF sends Paging message(s) to the NG-RAN node(s) per UE as described in step 4b in clause 4.2.3.3 of TS 23.502.
Step 6.
Receiving the paging, the UE(s) in CM-IDLE state sends Service Request message to the AMF, see clause 4.2.3 of TS 23.502.
After receiving the Service Request sent by the UE(s),
  • Either based on the received PDU Session ID in step 3, the AMF invokes steps 7a/7b to update the related PDU sessions; or:
  • Based on the received UE reachability Notification Address in step 3, the AMF identifies and notifies the related SMF of the UE(s), which are reachable now and the Location Information, by using the Namf_MT_UEReachabilityInfoNotify message. In this case, it can be a separated notification or combined with step 8.
Step 7a/7b.
Based on the received PDU Session ID in step 3, the AMF identifies the related SMF and invokes Nsmf_PDUSession_UpdateSMContext request. The SMF replies with Nsmf_PDUSession_UpdateSMContext response.
The SMF may also include the MBS assistance information for the MBS session in N2 SM Information, if the MBS subscription data from the UDM contains the MBS assistance information which includes the ID(s) of the MBS session(s) that the UE joined. The MBS assistance information for MBS session sent to the NG-RAN is described in clause 6.17. The procedure then continues at step 9.
Step 8a.
For UE(s) that do not respond to paging, the AMF informs the SMF of the paging failure in Namf_MT_UEReachabilityInfoNotify.
Step 8b.
For UE(s) that is indicated as reachable via the Namf_MT_UEReachabilityInfoNotify message, or user plane of the associated PDU session is activated already but the QoS profile(s) for associated QoS flow(s) needs to be provided for the PDU session, the SMF invokes Namf_Communication_N1N2MessageTransfer (N2 SM information ()) to the AMF same as described in step 4b.
The SMF may also include the MBS assistance information for the MBS session in N2 SM Information, if the MBS subscription data from the UDM contains the MBS assistance information which includes the ID(s) of the MBS session(s) that the UE joined. The MBS assistance information for MBS session sent to the NG-RAN is described in clause 6.17.
Step 9.
The AMF sends N2 request message (N2 SM information ()) to the RAN node.
Step 10a.
If the shared tunnel has not been established before, the shared tunnel is established at this step, as defined in clause 7.2.1.4. The NG-RAN configures UE with RRC messages if needed.
In this step or at later stage, NG-RAN may determine whether to apply delivery enabling reception by UEs in RRC_INACTIVE state for the MBS session, as defined in clause 6.17.
Step 10b.
Steps 8 to 12 defined in clause 7.2.1.3 are performed. If 5GC Individual MBS traffic delivery is used, the SMF configures the UPF for individual delivery and if necessary, requests the MB-SMF to configure the MB-UPF to send multicast data to the UPF.
Step 11.
If the MB-SMF finds out there are shared tunnel established, step11-15 are performed. The MB-SMF invokes Namf_MBSCommunication_N2MessageTransfer Request (TMGI, N2 SM Information (Activation, TMGI)) to the AMF for those NG-RAN nodes, which have shared tunnel with MB-UPF. This step may be performed in parallel with step 2.
Step 12.
The AMF sends NGAP activation request message (N2 SM Information ()) to the NG-RAN nodes. For those UEs that have joined in the MBS Session and are in RRC_INACTIVE state, the RAN nodes perform RAN paging as specified in TS 38.300. If Group paging is triggered, the NG-RAN may indicate that the MBS session data is allowed to be received in RRC_INACTIVE state as specified in clause 6.17.
Step 13.
The NG-RAN nodes responses to AMF by NGAP activation response message. The NG-RAN nodes establish radio resources to transmit multicast MBS session data to the UE(s).
In this step or at later stage, NG-RAN may determine whether to apply delivery enabling reception by UEs in RRC_INACTIVE state for the MBS session, as defined in clause 6.17.
If the NG-RAN determines that a UE receives the multicast MBS data in RRC_CONNECTED state, the NG-RAN shall not release the radio connection of a UE that has joined into the Multicast MBS session only because no unicast traffic is received for the UE.
Step 14.
AMF to MB-SMF: Namf_MBSCommunication_N2MessageTransfer Response ().
Step 15.
The MB-SMF sends N4mb Session Modification Request to the MB-UPF to forward the received MBS packets. The MB-UPF responds to the MB-SMF with N4mb Session Modification Response acknowledging the MB-SMF request.
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7.2.5.3  MBS session deactivation procedure  p. 92

Reproduction of 3GPP TS 23.247, Fig. 7.2.5.3-1: MBS session deactivation procedure
Figure 7.2.5.3-1: MBS session deactivation procedure
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In this procedure, steps 3 to 4 and steps 5 to 9 are executed in parallel.
Step 1.
The procedure may be triggered by the following events:
  • When MB-UPF detects there is no data receives for the MBS Session, MB-UPF sends MB-N4 Notification (N4 Session ID) to the MB-SMF for deactivating the MBS session.
  • AF sends MBS Deactivation request (TMGI) to the MB-SMF directly or via NEF.
Step 2.
The MB-SMF sends an N4mb Session Modification Request (TMGI, [Buffered Downlink Traffic detection]) to the MB-UPF. The Buffered Downlink Traffic detection is requested by MB-SMF to be informed by the MB-UPF about incoming MBS data. The MB-SMF triggers MBS session activation once informed. If the MBS session is to be activated via the AF request directly, the Buffered Downlink traffic detection is not needed, but the MB-SMF still instructs the MB-UPF to stop forwarding and possibly to buffer MBS data.
MB-UPF to MB-SMF: N4mb Session Modification Response acknowledging the MB-SMF request.
Step 3.
The MB-SMF sends Nmbsmf_MBSSession_ContextStatusNotify request (MBS Session ID) to the SMFs.
Based on the received MBS Session ID, the SMF sets the indicated multicast MBS session state to Inactive:
  • If the SMF finds out there are UE(s) that joined the indicated multicast MBS session and use 5GC Individual MBS traffic delivery, step 4 is performed for those UE(s).
  • If SMF find there are no UE(s) that joined the indicated MBS session and use 5GC Individual MBS traffic delivery, no further operation for SMF is required.
Step 4a.
[Conditional] For UE(s) for which the 5GC individual delivery is used, step 3b and steps 4-8 in clause 4.3.3.2 of TS 23.502 are performed to remove the associated QoS flow(s) related to the multicast MBS session.
Step 4b.
[Conditional] For UE(s) for which the 5GC individual delivery is used, the related SMF(s) may keep the shared tunnel that is used for Individual MBS traffic delivery over N19mb interface. If the SMF decides to release the shared tunnel, steps 3 to 6 in clause 7.2.2.2 need to be performed.
Step 5.
If the MB-SMF finds out there are shared tunnel established over N3mb interface, the MB-SMF sends Namf_MBSCommunication_N2MessageTransfer Request (TMGI, N2 SM information (Deactivation, TMGI)) to the AMFs.
Step 6.
The AMF sends NGAP deactivation request message (N2 SM information ()) to the NG-RAN nodes.
Step 7.
The NG-RAN node keeps the multicast MBS Session Context and N3mb shared tunnel for the multicast MBS session.
If the MBS Session Context indicates no UE for the multicast MBS session (e.g. due to UE becomes CM-IDLE state), the NG-RAN triggers release of the shared delivery as described in clause 7.2.2.4.
Step 8.
NG-RAN acknowledges the NGAP deactivation Response message.
Step 9.
The AMF invokes Namf_MBSCommunication_N2MessageTransfer Response to acknowledge the service for MB-SMF.
When the MBS session is in "Inactive" state and handover procedure is triggered, it is defined in clause 7.2.3.6.
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