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Content for  TS 23.247  Word version:  18.5.0

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7.1.1.2  MBS Session Creation without PCCp. 45

This procedure is used by the AF to start the MBS Session towards 5GC and consist of TMGI allocation, and MBS session creation, and they apply to both multicast and broadcast communications unless otherwise stated.
For multicast, MBS session establishment procedure triggered by UE join requests may follow the MBS session creation procedure to reserve resources towards NG-RAN. For broadcast, the MBS session start procedure to reserve resources towards NG-RAN is triggered by the MBS session creation procedure.
For both broadcast and multicast communication, the TMGI allocation may be separated from the MBS Session creation request.
For multicast communication, TMGI allocation procedure is applicable if TMGI is used as MBS Session ID.
Reproduction of 3GPP TS 23.247, Fig. 7.1.1.2-1: MBS Session Creation without PCC
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Steps 1 to 6 are optional and only applicable if TMGI is used as MBS Session ID and required to be pre-allocated.
Step 1.
AF sends Nnef_MBSTMGI_Allocate Request (TMGI number, [MBS service area]) message to NEF/MBSF to request allocation of a TMGI(s) to identify new MBS session(s). The MBS service area indicates the possible service area for those TMGI(s) to be allocated, which may be needed for local MBS.
Step 2.
NEF/MBSF checks authorization of AF. If geographical area information or civic address information was provided by the AF as MBS service area, NEF/MBSF performs the translation.
Step 3.
NEF/MBSF discovers and selects an MB-SMF using NRF or based on local configuration, possibly based on MBS service area.
If the NEF/MBSF discovers MB-SMF candidates based on MBS service area, and the MBS service area cannot be covered by the MB-SMF service area of a single MB-SMF, the NEF/MBSF rejects the TMGI allocation with an error information indicating that the MBS service area cannot be covered by the MB-SMF service area of a single MB-SMF. The subsequent steps are not executed.
Step 4.
NEF/MBSF sends an Nmbsmf_TMGI_Allocate Request (TMGI number) message to the MB-SMF.
Step 5.
MB-SMF allocates TMGI(s) and returns the TMGI(s) to the NEF/MBSF via the Nmbsmf_TMGI_Allocate response (TMGI(s), expiration time).
Step 6.
The NEF or MBSF responds to the AF by sending an Nnef_MBSTMGI_Allocate Response (TMGI(s), expiration time).
Step 7.
The AF may perform a Service Announcement towards UEs. The AF informs UEs about MBS Session information with MBS Session ID, e.g. TMGI, SSM, and possibly other information e.g. MBS service area, session description information, etc.
The MBS service area information can be Cell ID list, TAI list, geographical area information or civic address information. Amongst them, Cell ID list and TAI list shall only be used by AFs who reside in trust domain, and when the AFs are aware of such information.
The UE needs to be aware if the service is broadcast or multicast to decide if JOIN is to be performed.
Step 8.
AF of content provider may provide description for an MBS session (possibly providing information for a previously allocated TMGI to NEF via a Nnef_MBSSession_Create request ([MBS Session ID], MBS service type, MBS Service Information, [TMGI allocation request], [MBS service area], [Any UE indication], [start and end time of the MBS session], [MBS session state], [ingress transport address request indication], [Request for location-dependent session], [FSA ID(s)], [Associated Session Identifier], [NR RedCap UE Information]). If steps 1-6 have not been executed before, the AF may provide an MBS Session ID containing an SSM or it may request that the network allocates an MBS Session ID (i.e. TMGI). The AF provides the MBS service type (i.e. either multicast service or broadcast service) and MBS Service Information (as defined in clause 6.14). The AF may provide the "Any UE indication" (indicating whether a multicast MBS session is "open to any UEs"), MBS service area, start and end time of the MBS session and MBS session state (active/inactive). In addition, the AF request may also indicate that the allocation of an ingress transport address is requested and that the AF request is for a location dependent MBS service.
If geographical area information or civic address information was provided by the AF as MBS service area, NEF/MBSF translates the MBS service area to Cell ID list or TAI list.
For broadcast communication, the AF may determine MBS FSA ID(s) for the Broadcast MBS session based on business agreements and include them in the description of the MBS session.
For broadcast communication, to support resource sharing across MBS Sessions during network sharing (see clause 6.18), the AF may include Associated Session Identifier in this step to enable NG-RAN to identify the broadcast MBS sessions from multiple CNs delivering the same content.
For broadcast communication, the AF may include the information that the broadcast MBS session is intended for NR RedCap UEs only or both for NR RedCap UEs and non-RedCap UEs in the "NR RedCap UE Information" parameter (as defined in clause 6.19).
Step 9.
NEF/MBSF checks authorization of content provider.
Step 10.
NEF/MBSF discovers MB-SMF candidates and selects MB-SMF as ingress control node, possibly based on MBS service area. If a TMGI is included in step 8, NEF/MBSF finds MB-SMF based on that TMGI.
If the NEF/MBSF discovers MB-SMF candidates based on MBS service area, and the MBS service area is not covered by the MB-SMF service area of a single MB-SMF, the NEF/MBSF rejects the TMGI allocation with an error information indicating that the MBS service area cannot be covered by the MB-SMF service area of a single MB-SMF. The flow continues in step 20 below.
Step 11.
NEF/MBSF sends Nmbsmf_MBSSession_Create Request ([MBS Session ID], MBS service type, [TMGI allocation request], MBS Service Information (as defined in clause 6.14), [MBS service area], [Any UE indication], [start and end time of the MBS session], [MBS session state], [ingress transport address request indication], [FSA ID(s)], [Associated Session Identifier], [multicast session security context], [NR RedCap UE Information]) to MB-SMF, to request MB-SMF to reserve ingress resources for a MBS distribution session. The NEF/MBSF forwards all parameters it has received from the AF in step 8. If the MBSF decides to insert an MBSTF into the user plane for the MBS session, it also indicates that the allocation of an ingress transport address is requested even if this was not requested in step 8. The request also includes the Any UE indication if provided in step 8. If the MBSF acts as the MBS security function for multicast as defined in TS 33.501, it provides a multicast session security context for the MBS session.
If requested to do so, or if a source specific multicast is provided as MBS Session ID in step 11, the MB-SMF allocates a TMGI.
For broadcast communication, if no MBS FSA ID(s) have been received, the MB-SMF selects MBS FSA ID(s) for the Broadcast MBS session based on local configuration.
If the MBS service area received in this step cannot be covered by the MB-SMF service area of the MB-SMF, the MB-SMF reduces the MBS service area to be within the MB-SMF service area and continues the procedure using the reduced MBS service area.
For broadcast communication, the NEF/MBSF forwards the "NR RedCap UE Information" parameter, if received from the AF.
Step 12.
Void.
Step 13.
The MB-SMF derives the required QoS parameters locally based on the MBS Service Information.
Step 14.
MB-SMF selects the MB-UPF. If the allocation of an ingress transport address was requested in step 11, the MB-SMF requests the MB-UPF to reserve user plane ingress resources. If multicast transport of the MBS data towards RAN nodes is to be used, the MB-SMF also request the MB-UPF to reserve for the outgoing data a tunnel endpoint and the related identifiers (source IP address, SSM and GTP Tunnel ID) and to forward data received at the user plane ingress resource using that tunnel endpoint.
If the allocation of an ingress transport address was not requested in step 11, the MB-SMF provides the SSM received as MBS Session ID to the MB-UPF and requests the MB-UPF to join the corresponding multicast tree from the content provider. The MB-SMF may also defer the configuration to join the corresponding multicast tree e.g. based on information that the session is inactive, service requirements and MBS start/end time until receiving the first query for the MBS session as part of the establishment procedure in clause 7.2.1.3, or until receiving a request to activate the MBS session via the MBS Session Update procedure in clause 7.1.1.6.
Step 15.
If requested, MB-UPF selects an ingress address (IP address and port) and a tunnel endpoint for the outgoing data and provides it to MB-SMF.
Step 16.
The MB-SMF sends an Nmbsmf_MBSSession_Create response ([TMGI], [Allocated ingress address], [Information of area reduction]).
MB-SMF indicates the possibly allocated ingress address to the NEF/MBSF. MB-SMF may include TMGI if it is allocated in step 11. For broadcast communication, the MB-SMF includes any MBS FSA ID(s) selected in step 11.
If the MB-SMF reduces the service area in step 11, the MB-SMF includes result information in the response indicating that the MBS service area cannot be covered by the MB-SMF service area of a single MB-SMF, and includes the Information of area reduction that relates to the reduced MBS service area.
Step 16a.
If a source specific multicast address is provided as MBS Session ID in step 11, the MB-SMF updates its NF profile at the NRF with the serving MBS Session ID. If an MBS service area was received in step 11, the MB-SMF updates its NF profile at the NRF with that information.
Step 17.
For broadcast communication, the MB-SMF continues the procedure towards the AMF and NG-RAN as specified in clause 7.3.1 to request the allocation of resources to for the transmission of the broadcast session.
Step 18.
[Optional] If the MBSF decides to use an MBSTF, the NEF/MBSF provides the ingress address received in step 16 towards the MBSTF as DL destination. If the allocation of an ingress transport address was requested in step 8, the MBSF requests the MBSTF to allocate the user plane ingress resources. If the allocation of an ingress transport address was not requested in step 8, the MBSF provides the SSM received as Multicast session ID in step 8 and requests the MBSTF to join the corresponding multicast tree from the content provider.
Step 19.
[Conditional on step 19] If requested, the MBSTF selects an ingress address (IP address and port) and provides it to NEF/MBSF.
Step 20.
The NEF/MBSF indicates the possibly allocated ingress address and other parameters (e.g. TMGI) to the AF via an Nnef_MBSSession_Create response ([TMGI], [Allocated ingress address], [Information of area reduction]). If MBS Session ID is not provided in step 8, or the MBS Session ID is SSM, the NEF/MBSF provides the allocated TMGI. If AF requested the allocation of an ingress transport address, the message also includes the allocated ingress address. For broadcast communication, the message also includes any MBS FSA ID(s) received in step 17.
If the NEF/MBSF rejects the TMGI allocation in step 10, or receives the result information in step 16 indicating that the MBS service area cannot be covered by the MB-SMF service area of the MB-SMF, the NEF/MBSF includes that result information, and forwards the Information of area reduction.
Step 21.
Same as step 7. The AF may also perform a service announcement at this stage.
Step 22.
For multicast communication, depending on configuration UEs can join the MBS Session as specified in clause 7.2.1.
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