Section: 4.15.9.5.1 Network timing synchronization status
Content: Figure 4.15.9.5.1-1: Procedure for TSCTSF subscription to RAN and/or UPF/NW-TT timing synchronization status 0. The AF requests creation or modification of ASTI or PTP based time synchronization service as described in clauses 4.15.9.4 and 4.15.9.3 including clock quality detail level and clock quality acceptance criteria (if applicable) in the request. If the request is received at the NEF, it checks whether the AF is authorized to send the request and forwards the request to the TSCTSF. If network timing synchronization status reports are provisioned using node-level signalling via control plane, the TSCTSF determines the serving AMF(s) and the UPF/NW-TT nodes (if applicable) for the UE(s) that needs to initiate network timing synchronization status monitoring. Otherwise, if network timing synchronizations status reports are provisioned via OAM, steps 1-3 and 5-7 are skipped. 1-2. (When the procedure is triggered by the AF request to influence the 5G access stratum time distribution or by PTP instance activation, modification): Upon the reception of the clock quality detail level and clock quality acceptance criteria (if applicable) in the AF request in step 0, the TSCTSF needs to be subscribed to NG-RAN timing synchronization status updates at the NG-RAN nodes that may provision access stratum time distribution information to the target UE. NG-RAN timing synchronization status updates provisioning may be configured via AMF (with node level signalling as illustrated in steps 1-2). The TSCTSF sends Namf_Communication_NonUeN2InfoSubscribe to initiate the subscription for the NG-RAN timing synchronization status updates from the AMF. As part of this subscription, the TSCTSF may specify TA(s) and/or NG-RAN node(s) in the subscription for the timing synchronization status reporting. Based on local configuration and/or TA or NG-RAN node information as received from the TSCTSF, the AMF may subscribe to some or all NG-RAN nodes in the TA(s) for the timing synchronizations status reporting. 3. (When the procedure is triggered by the AF request for PTP instance activation, modification and if the UPF/NW-TT is involved in providing time information to DS-TT): Upon the reception of the clock quality acceptance criteria in the AF request in step 0, the TSCTSF needs to be subscribed to UPF/NW-TT timing synchronization status updates at the UPF/NW-TT that may provision time information via PTP to the target UE. UPF/NW-TT timing synchronization status updates provisioning may be configured via OAM or via UMIC. 4. The RAN node is pre-configured for the thresholds for each timing synchronization status attribute as described in clause 5.27.1.12 of TS 23.501[ System architecture for the 5G System (5GS) ]  [2]. When the network timing synchronization status exceeds or meets again any of the pre-configured thresholds, the NG-RAN node detects a change on its timing synchronization status (e.g., degradation, failure, improvement). 5-6. If the NG-RAN node detects a change on its timing synchronization status as described in clause 5.27.1.12 of TS 23.501[ System architecture for the 5G System (5GS) ]  [2] and the timing synchronization status reporting is configured via the AMF in step 1, the NG-RAN node notifies the AMF providing a NG-RAN timing synchronization status update. The update can contain the information elements listed in Table 5.27.1.12-1 of TS 23.501[ System architecture for the 5G System (5GS) ]  [2], and the scope of the timing synchronization status (as described in clause 5.27.1.12 of TS 23.501[ System architecture for the 5G System (5GS) ]  [2]). The AMF forwards the update to the subscribed TSCTSF. 7. If the UPF/NW-TT detects a change on its timing synchronization status and timing synchronization status reporting is configured via UMIC in step 3, the UPF/NW-TT notifies the TSCTSF providing a UPF/NW-TT timing synchronization status update via UMIC. The update can contain the information elements listed in Table K.1-2 of TS 23.501[ System architecture for the 5G System (5GS) ]  [2]. 8. Upon the reception of a change in the NG-RAN and/or NW-TT timing synchronization status update, the TSCTSF shall determine if the UE is impacted and whether the clock quality acceptance criteria can still be met. For each scope of the timing synchronization status received from the RAN in step 6, if the status indicates degradation or failure, TSCTSF may set the Area of Interest to gNB node ID(s) or Cell IDs in the scope of the timing synchronization status. The TSCTSF uses the resulted Area of Interest to subscribe for the UE presence in Area of Interest from the AMF that is serving the gNB node ID as described in clause 5.27.1.12 of TS 23.501[ System architecture for the 5G System (5GS) ]  [2]. If the status indicates recovery, the TSCTSF may remove the corresponding scope from the subscription. Upon reception of notification for the UE presence in the Area of Interest, if the TSCTSF determines that the UE is impacted for ASTI service, the TSCTSF performs steps 15-16 in clause 4.15.9.4 to notify the AF the acceptance criteria result. Upon reception of notification for the UE presence in the Area of Interest, if the TSCTSF determines that the UE is impacted for PTP service, the TSCTSF performs steps 9-11 in clause 4.15.9.3.2 to notify the AF the acceptance criteria result.