5.35A.4 MBSR authorization

For a MBSR, the subscription information stored in the HPLMN indicates whether it is authorized to operate as MBSR and the corresponding location and time information as specified in TS 23.502 [3].

NOTE 1: For non-roaming MBSRs, the operator local policy can be taken into consideration for MBSR authorization, e.g. based on the network status, or a limit on the number of MBSRs operating in a certain area.

When the MBSR (IAB-UE) performs initial registration with the serving PLMN, it indicates the request to operate as a MBSR as described in clause 5.35A.1. The AMF authorizes the MBSR based on the subscription information and provides MBSR authorized indication to the MBSR node over NAS and NG-RAN over NGAP as described in the registration procedure in TS 23.502 [3]. The MBSR establishes the connection to OAM system using the configuration information for MBSR operation upon the reception of MBSR authorization indication (authorized). The MBSR provides the information about the authorization result (authorized) to its IAB gNB-DU component. When the AMF formulates the registration area for an authorized MBSR, the TAs included in the registration area are authorized for MBSR operation homogenously, taking any MBSR Operation allowed information in subscription data and operator local policy into account.

NOTE 2: The MBSR support can be deployed in certain Network Slices based on operator configuration and Network slicing functionalities (e.g. the function specified in clause 5.15.18) can be applied when suitable.

When MBSR roaming is supported, a roaming agreement between VPLMN and HPLMN regarding MBSR operation is in place. The AMF can make use of the subscription data for authorization of the MBSR in the V-PLMN.

MBSR (IAB gNB-DU) can use IAB-node integration procedure or inter-IAB-donor gNB mobility procedure to integrate into the serving PLMN to provide service.

NOTE 3: How the MBSR obtains the configuration information for MBSR operation is described in clause 5.35A.2.

If the MBSR operation is not authorized (e.g. due to location or time limitation, or due to lack of authorization altogether to operate as MBSR), the AMF of the MBSR (IAB-UE) can indicate to the MBSR (IAB-UE) that it is not allowed to act as an MBSR, i.e. the MBSR authorization indication (not authorized), as part of registration procedure. The AMF may provide the indication in a Registration Accept (if the PLMN allows the MBSR IAB-UE to be registered in the PLMN). In this case, the AMF includes the MBSR authorization indication (not authorized) to IAB-donor-gNB. The MBSR provides the information about the authorization result (not authorized) to its IAB-DU component. The AMF may reject the Registration (if the PLMN does not allow the MBSR IAB-UE to be registered in the PLMN).

When the MBSR authorization state changes for a registered MBSR node (either authorized, or not authorized), the AMF of the MBSR (IAB-UE) updates the MBSR (IAB-UE) and the NG-RAN accordingly. Based on the operator configuration, the AMF may use either Deregistration (with re-registration required indication) or the UE Configuration Update procedure to inform the MBSR regarding the updated authorization status:

• The Deregistration with re-registration required indication procedure is used, when the AMF of the MBSR (IAB-UE) intends to keep the MBSR (IAB-UE) registered. The AMF of the MBSR (IAB-UE) provides the new authorization indication to MBSR (IAB-UE) as described above, when the MBSR performs initial Registration procedure after the deregistration.
• The Deregistration procedure without re-registration required indication is used if the PLMN does not allow the MBSR (IAB-UE) to remain registered in the PLMN.
• When UE Configuration Update procedure is used, the AMF provides the new authorization indication to the MBSR (IAB-UE) in the UE Configuration Update Command. The MBSR provides the information about the new authorization status to its IAB-DU component.

The AMF of the MBSR (IAB-UE) informs the NG-RAN (i.e. the IAB-donor gNB) of the new authorization status using UE Context Modification, Initial Context Setup procedure or the DOWNLINK NAS TRANSPORT message, with the following principles:

• If the authorization state changes from authorized to not authorized and AMF uses the UE Configuration Updated procedure to update the MBSR, the AMF updates the NG-RAN with the new authorization indication (not authorized) by including this information in the DOWNLINK NAS TRANSPORT message. The NG-RAN completes handover of the UEs served by the MBSR before releasing the F1 connection to the MBSR IAB-DU.
• If the authorization state changes from authorized to not authorized and the AMF uses the Deregistration procedure to update the MBSR, the AMF sends the UE Context Modification message to NG-RAN with the authorization indication as not authorized. Then, if the AMF receives a NGAP UE CONTEXT RELEASE REQUEST message from the NG-RAN with a cause code indicating the NG-RAN node has completed the operation for a non-authorized MBSR, including e.g. the handover of the UEs the MBSR was serving as defined in TS 38.413 [34], or after a certain period (e.g. based on the expiration of a timer configured on the AMF) the AMF executes the deregistration procedure with MBSR and releases the NAS signalling connection.

If the Network-initiated Deregistration procedure is triggered for MBSR (IAB-UE) that is registered with authorization to act as MBSR, the AMF sends the UE Context Modification message to the NG-RAN (i.e. the IAB-donor gNB) and updates the NG-RAN with the authorization indication as not authorized. Then, if the AMF receives a NGAP UE CONTEXT RELEASE REQUEST message from the NG-RAN with a cause code indicating that the NG-RAN node has completed the operation for a non-authorized MBSR, including e.g. the handover of the UEs the MBSR was serving as defined in TS 38.413 [34], or after a certain period (e.g. based on the expiration of a timer configured on the AMF) the AMF executes the deregistration procedure with MBSR and releases the NAS signalling connection.

NOTE 4: The AMF delays the MBSR de-registration to allow the IAB-donor gNB to move all connected UEs via MBSR to other cells as specified in clause 8.9.10 of TS 38.401 [42].

If a PDU session is used to provide OAM access for MBSR when it is not authorized but remains registered, the AMF of the MBSR (IAB-UE) may notify the SMF serving the PDU session for O&M access to trigger the release of the PDU Session.

NOTE 5: The mechanism applies to both roaming and non-roaming MBSR operations.