Section: 4.28.3.1 Control of (g)PTP time synchronization service without AF request
Content: The TSCTSF may use the subscription data to control the (g)PTP-based time distribution without AF request. Figure 4.28.3.1-1: Subscription based control of (g)PTP time synchronization service without AF request 1. The UE performs the UE-requested PDU Session Establishment. 2. The PCF determines if the PDU Session is potentially impacted by time synchronization service and invokes Npcf_PolicyAuthorization_Notify service operation to the TSCTSF discovered and selected for time synchronization to indicate there is a UE connected to a specific DNN/S-NSSAI configured for (g)PTP-based time distribution. The TSCTSF retrieves the UE SUPI using IP address and /or DNN/S-NSSAI from BSF as specified in the clause 4.15.10. 3. The TSCSTF uses the SUPI to retrieve the Time Synchronization Subscription Data available at the UDM. 4. The TSCTSF controls the (g)PTP-based time synchronization service based on the Time Synchronization Subscription Data as defined in clause 5.27.1.11 of TS 23.501[ System architecture for the 5G System (5GS) ]  [2]. If the Time Synchronization Subscription Data contains: a) one or more Subscribed Time Synchronization Service ID(s) that can be mapped to PTP instance configuration(s), the TSCTSF determines if one or more of the PTP instance configurations match with the DNN/S-NSSAI of the given PDU Session. The TSCTSF stores information that the time-synchronization service cannot be controlled by an AF for the given SUPI. b) An indication that an AF-requested (g)PTP time synchronization service is allowed for the given UE and DNN/S-NSSAI, the TSCTSF adds the given SUPI to the list of SUPIs for which the time-synchronization service can be controlled by an AF. c) If TSCTSF receives neither a) nor b), the TSCTSF assumes that the time-synchronization service cannot be controlled by an AF for the given SUPI. The TSCTSF releases the AF-session with the PCF. 5. For each matching PTP instance configuration determined in step 4, if no PTP instance exists for the given PTP instance configuration, the TSCTSF initializes the PTP instance in 5GS as described in clause K.2.2 of TS 23.501[ System architecture for the 5G System (5GS) ]  [2]. The TSCTSF configures a PTP port in DS-TT and adds it to the corresponding PTP instance in NW-TT as described in clause K.2.2 of TS 23.501[ System architecture for the 5G System (5GS) ]  [2]. The TSCTSF uses the procedure in clause 4.15.9.4 to activate or modify the 5G access stratum time distribution for the UE. If the PTP instance configuration referenced by the Time Synchronization Subscription data for the UE contains start and stop times or a coverage area, the TSCTSF updates the PTP port for the corresponding PTP instance as defined in clause 5.27.1.11 of TS 23.501[ System architecture for the 5G System (5GS) ]  [2]. The TSCTSF uses the procedure in clause 4.15.9.4 to activate or deactivate the 5G access stratum time distribution for the UEs that are part of the impacted PTP instance. 6. If a coverage area is included in the subscription data for UE related to the PTP instance, TSCTSF discovers the AMF(s) serving the TA(s) defined for the time synchronization coverage area (Area of Interest) and subscribe to receive notifications in UEs presence in the Area of Interest. Based on the outcome the TSCTSF determines whether to activate or deactivate the time synchronization service for the impacted PTP instance. The TSCTSF will activate/deactivate the service by modifying the PTP instance configuration as described in clause K.2.2 of TS 23.501[ System architecture for the 5G System (5GS) ]  [2].