5.27.1.11 Controlling time synchronization service based on the Subscription

The distribution of timing information, 5G access stratum-based time distribution and (g)PTP-based time distribution, for a UE may be controlled based on subscription data stored in the UDM. The (g)PTP-based or 5G access stratum-based time synchronization service may be provided to a UE based on the UE's subscription which is specified in the TS 23.502 [3] clause 5.2.3.3.1.

The Access and Mobility Subscription data include the following information for the control of 5G access stratum-based time distribution:

• the Access Stratum Time Synchronization Service Authorization, which indicates whether the UE should be provisioned with 5G system internal clock timing information over access stratum as specified in TS 38.331 [28].
• optionally, the Uu time synchronization error budget.
• optionally, one or more periods of start and stop times defining the times when the UE should be provisioned with 5G system internal clock timing information.
• optionally, a Time Synchronization Coverage Area comprising a list of TAs where the UE shall be provisioned with 5G system internal clock timing information.
• optionally, a clock quality detail level indicating whether and which clock quality information to provide to the UE. It comprises one of the following values: clock quality metrics or acceptable/not acceptable indication.
• optionally, the clock quality acceptance criteria for the UE. It may be defined based on one or more attributes listed in Table 5.27.1.12-1.

During the Registration procedure, the AMF retrieves the subscription from UDM. If the AMF receives 5G access stratum-based time synchronization service subscription for the given UE, the AMF controls the 5G access stratum-based time distribution:

• If the 5G access stratum-based time synchronization service is allowed for the UE, the AMF provides the 5G access stratum time distribution indication to the NG-RAN so that it can provide 5G timing information to the UE.
• The AMF may provide a Uu time synchronization error budget to the NG-RAN (as described in clause 5.27.1.9). If the UE's subscription contains a Uu time synchronization error budget, then AMF sends it to NG-RAN. Otherwise, the AMF uses the pre-configured Uu time synchronization error budget and sends it to NG-RAN.
• If the UE's subscription contains Coverage Area (defined as a list of TAs), the AMF configures the NG-RAN to provide the 5G timing information to UE only when the UE is in the Coverage Area as described in clause 5.27.1.10.
• If the AMF receives the start and stop times, then the AMF enables and disables the 5G access stratum time distribution indication to the NG-RAN according to the expiry of start and stop times if the UE is in CM-CONNECTED state. If the UE is in CM-IDLE state when a Start time condition is met, the AMF pages the UE and provides the 5G access stratum time distribution indication to NG-RAN as part of the subsequent service request procedure initiated by the UE in the response to the paging.
• If the AMF receives the clock quality detail level, then the AMF configures the NG-RAN to provide clock quality detail information reporting to UE as described in clause 5.27.1.12. The AMF may instruct the UE to reconnect to the network when the UE detects that the RAN timing synchronization status has changed while the UE is in RRC_INACTIVE or RRC_IDLE, as described in clause 5.27.1.12.
• If the AMF receives the same parameters both in the Access and Mobility Subscription data from UDM and in the AM Policy from PCF, the AMF shall use the value received from the AM policy.

The Time Synchronization Subscription data is the subscription data for the control of (g)PTP-based time distribution and 5G access stratum-based time distribution and includes the following information:

• the "AF request Authorization", indicating whether the UE is authorized for an AF-requested 5G access stratum-based time distribution and (g)PTP-based time distribution services. The indication is provided separately for each service:
• "allowed" or "not allowed" for (g)PTP based time synchronization service (per DNN/S-NSSAI and UE identity),
• "allowed" or "not allowed" for ASTI based time synchronization services (per UE identity).
• If the "AF request Authorization" is set to "allowed", the Time Synchronization Subscription data may contain additional information for authorization of (g)PTP- and ASTI- based time synchronization services: this information is optional and may be provided separately for authorization of each service:
• optionally, a list of TA(s) which specifies an area (a so-called Authorized Time Synchronization Coverage Area) in which an AF may request time synchronization services;
• optionally, one or more periods of authorized start and stop times, which indicates the allowed time period during which an AF may request time synchronization services;
• optionally, authorized Uu time synchronization error budget, which indicates the limit the AF may request.
• optionally, "allowed" or "not allowed" for clock quality detail level equals to "clock quality metrics", which indicates whether clock quality metrics information may be provided to the UE.
• optionally, "allowed" or "not allowed" for clock quality detail level equals to "acceptable/not acceptable indication", which indicates whether an acceptable/not acceptable indication may be provided to the UE.
• optionally, one or more sets of clock quality acceptance criteria for the UE using the TSS attributes as defined in clause 5.27.1.12.

NOTE 1: If the clock quality detail level set to "acceptable/not acceptable indication" is "allowed", clock quality acceptance criteria need to be provided.

• one or more Subscribed time synchronization service ID(s), each containing the DNN/S-NSSAI and a reference to a PTP instance configuration pre-configured at the TSCTSF (e.g. PTP profile, PTP domain, etc.):
• optionally, for each PTP instance configuration, one or more periods of start and stop times defining active times of time synchronization service for the PTP instance.
• optionally, for each PTP instance configuration, a Time Synchronization Coverage Area defining a list of TAs where the (g)PTP-based time synchronization is available for the UEs in the PTP instance.
• optionally, for each PTP instance configuration, Uu time synchronization error budget.

The TSCTSF retrieves the Time Synchronization Subscription data from UDM. If the TSCTSF receives the Time Synchronization Subscription data for a UE, the TSCTSF controls the Time Synchronization Service including (g)PTP-based time distribution and 5G access stratum-based time distribution:

• The TSCTSF retrieves the Time Synchronization Subscription data from the UDM when the TSCTSF receives an AF request for the time synchronization service (either ASTI or (g)PTP). According to the "AF request Authorization" in the UE's Time Synchronization Subscription data, the TSCTSF determines whether the UE is authorized for an AF-requested time synchronization service:
• If the UE's Time Synchronization Subscription data contains an Authorized Time Synchronization Coverage Area (i.e. a list of TA(s) defining the restricted area for AF request), TSCTSF checks whether the AF requested Coverage Area satisfies the authorized area: If the requested Coverage Area (see clause 5.27.1.10) is within the Authorized Time Synchronization Coverage Area, the TSCTSF uses the requested Coverage Area. If the Authorized Time Synchronization Coverage Area is inside of the requested Coverage Area, the TSCTSF uses the Authorized Time Synchronization Coverage Area. If the requested Coverage Area partly overlaps with the Authorized Time Synchronization Coverage Area, the TSCTSF uses the intersection of them. If there is no overlap between them, the TSCTSF shall reject the AF request.
• If the AF requested Coverage Area satisfies the authorized area totally or partly, TSCTSF notifies to AF with the Time Synchronization Service information based on the Authorized Time Synchronization Coverage Area. TSCTSF subscribes to UE's presence in the Area of Interest at the discovered AMF(s), if the UE(s) moves out of the Time Synchronization Coverage Area requested by AF or updated by TSCTSF, the TSCTSF shall disable Time Synchronization Service and notifies to AF.
• If the UE's Time Synchronization Subscription data contains authorized Uu time synchronization error budget, the TSCTSF checks whether the Uu time synchronization error budget derived from AF request satisfies (i.e. equal or larger than) the authorized Uu time synchronization error budget.
• If the UE's Time Synchronization Subscription data contains periods of authorized start and stop times, the TSCTSF checks whether the AF requested temporal validity condition satisfies (i.e. within) any of the periods of authorized start and stop times. If such period is found, the TSCTSF uses the start and stop times of the AF request.
• If the UE's Time Synchronization Subscription data contains a clock quality detail level (and clock quality acceptance criteria, if applicable), the TSCTSF checks whether the AF-requested clock quality information to be reported complies with the authorized clock quality detail level and the clock quality acceptance criteria (if applicable) in the UE's Time Synchronization Subscription data.

Each parameter in the AF-requested clock quality is evaluated individually, if the TSCTSF determines that at least one parameter is "not acceptable", the TSCTSF rejects the AF request.

If the "Traceable to GNSS" in the subscription data is "Yes", the AF request for Traceable to GNSS is allowed. Otherwise, the AF request for Traceable to GNSS is not allowed.

If the "Traceable to UTC" in the subscription data is "Yes", the AF request for Traceable to UTC is allowed. Otherwise, the AF request for Traceable to UTC is not allowed.

For Frequency stability and Clock Accuracy, AF is not allowed to request value which is lower than value in subscription data.

• If the AF request is authorized, the TSCTSF proceeds as specified in clause 5.27.1.8 and in TS 23.502 [3]. Otherwise, the TSCTSF rejects the AF request.
• The TSCTSF retrieves the Time Synchronization Subscription data from the UDM when it receives notification from the PCF that a UE has established a PDU Session that is potentially impacted by (g)PTP-based time synchronization service:
• The TSCTSF retrieves the PTP instance configurations referenced from the "Subscribed time synchronization service ID(s)". The PTP instance configurations are stored locally in the TSCTSF. The TSCTSF determines if one or more of the PTP instance configurations match with the DNN/S-NSSAI of the given PDU Session. 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.
• 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.
• If the PTP instance configuration referenced by UE's Time Synchronization Subscription data contains an Uu time synchronization error budget, then the TSCTSF uses it to derive an Uu time synchronization error budget available for the NG-RAN to provide the 5G access stratum time for the UE as specified in clause 5.27.1.9.
• If the PTP instance configuration referenced by the Time Synchronization Subscription data for the UE contains start and stop times, the TSCTSF, upon expiry of start time, creates the PTP instance and adds the PTP port in DS-TT to the PTP instance. Upon expiry of stop time, if this is the last period of start and stop times in the PTP instance configuration, the TSCTSF deletes the PTP instance, otherwise the TSCTSF temporarily removes the PTP port in DS-TT from the corresponding PTP instance as specified in clause 4.15.9.3 of TS 23.502 [3].
• If the PTP instance configuration referenced by the Time Synchronization Subscription data for the UE contains a Time Synchronization Coverage Area, the TSCTSF subscribes to UE's Presence in Area(s) of Interest corresponding to the Time Synchronization Coverage Area at the discovered AMF(s). When the TSCTSF determines that the UE has moved inside or outside of the Time Synchronization Coverage Area, the TSCTSF adds or temporarily removes the PTP port in DS-TT from the corresponding PTP instance.