4.15.9 Time Synchronization exposure

23.5023GPPProcedures for the 5G System (5GS)Release 18TS

Tools: ARFCN - Frequency Conversion for 5G NR/LTE/UMTS/GSM

4.15.9.1 General

Time synchronization exposure allows an AF to configure time synchronization in 5GS. For (g)PTP operation, the Time synchronization service allows an AF to subscribe to the UE and 5GC capabilities and availability for time synchronization service (as described in clause 4.15.9.2) and to configure the (g)PTP instance in 5GS as described in clause 4.15.9.3. For 5G access stratum based time distribution, the AF can influence the 5G access stratum time distribution as described in clause 4.15.9.4. The time synchronization exposure is provided by NEF that uses the service provided by TSCTSF. The AF that is part of operator’s trust domain may invoke the services directly with TSCTSF and TSCTSF responds/notifies directly to the AF, accordingly.

NOTE: The AF can use either the procedure for configuring the (g)PTP instance in 5GS as described in clause 4.15.9.3 or the procedure for controlling the 5G access stratum time distribution as described in clause 4.15.9.4 for a particular UE. The procedures are not intended to be used in conjunction with each other by the AF. However, the (g)PTP instance activation, modification, and deactivation can influence the 5G AS time distribution for the UEs that are part of the impacted PTP instance.

4.15.9.2 Exposure of UE availability for Time Synchronization service

The procedure is used by the AF to subscribe to notifications and to explicitly cancel a previous subscription for UE availability for time synchronization service. Cancelling is done by sending Nnef_TimeSynchronization_CapsUnsubscribe request identifying the subscription to cancel with Subscription Correlation ID.

Figure 4.15.9.2-1: Procedure for exposing 5GS and/or UE availability and capabilities for Time Synchronization services

1. Upon PDU Session establishment, the PCF determines if the PDU Session is potentially impacted by time synchronization service (based on local configuration or 5GS Bridge information event from SMF as described in SM Policy Association Establishment procedure in clause 4.16.4). In this case the PCF invokes Npcf_PolicyAuthorization_Notify service operation to the TSCTSF discovered and selected as described in clause 6.3.24 of TS 23.501 [2]. The Npcf_PolicyAuthorization_Notify service operation includes the UE address of the PDU Session and DNN/S-NSSAI.

NOTE: In the case of private IPv4 address being used for the UE, the DNN and S-NSSAI are required for session binding in the PCF.

The PCF registers to BSF as described in TS 23.503 [20]. TSCTSF invokes a Npcf_PolicyAuthorization_Create request message to the PCF and stores the DNN, S-NSSAI and IP address as received from PCF and SUPI as received from BSF and associates them with the AF-session.

If PMIC/UMIC information from the DS-TT or NW-TT is available at the PCF, the PCF reports it to the TSCTSF invoking Npcf_PolicyAuthorization_Notify.

2. The AF subscribes to the UE availability for time synchronization service and provides the associated Notification Target Address of the AF by sending Nnef_TimeSynchronization_CapsSubscribe request.

Report Type defines the type of reporting requested (e.g. one-time reporting, periodic reporting or event based reporting).

The request may include DNN and slicing information (S-NSSAI) and shall include an AF-Service-Identifier. If the DNN and S-NSSAI are omitted in the request, the NEF uses the AF-Service-Identifier to determine the target DNN and slicing information (S-NSSAI).

The Event Filter may include a list of UE identities (GPSIs) or Groups of UEs identified by an External Group Identifier that further define the subset of the target UEs. If the request does not include UE identities nor External Group Identifier, the request is targeted to any UE with a PDU Session using the DNN and S-NSSAI. The NEF forwards the GPSIs or the External Group Identifier to the TSCTSF by including them/it inside the Ntsctsf_TimeSynchronization_CapsSubscribe request.

Additionally, the Event Filter may include one or more of the requested PTP instance type, requested transport protocol for PTP, or requested PTP Profile as described in Table 5.2.6.25.6-1.

When the NEF processes the AF request the AF-Service-Identifier may be used to authorize the AF request.

Depending on the AF-Service-Identifier and/or DNN/S-NSSAI, the NEF may reject the request if the list of UE identities or External Group Identifier is not included in the request.

To unsubscribe to the UE availability for time synchronization for a list of UE(s), the AF invokes Nnef_TimeSynchronization_CapsUnsubscribe service operation and provides the Subscription Correlation ID.

3. (In the case of Ntsctsf_TimeSynchronization_CapsSubscribe): The NEF discovers the TSCTSF as described in clause 6.3.24 of TS 23.501 [2]. The NEF invokes the Ntsctsf_TimeSynchronization_CapsSubscribe request service operation to the selected TSCTSF.

(In the case of Ntsctsf_TimeSynchronization_CapsUnsubscribe): The NEF uses the Subscription Correlation ID to determine the TSCTSF and interacts with the TSCTSF by triggering a Ntsctsf_TimeSynchronization_CapsUnsubscribe request message.

The AF that is part of operator’s trust domain may invoke the services directly with TSCTSF.

4. If the Event Filter includes GPSI(s), an External Group Identifier or an Internal Group Identifier, the TSCTSF uses the Nudm_SDM_Get request to retrieve the subscription information (SUPI(s)) from the UDM using each GPSI or the External Group Identifier as received from the NEF or an Internal Group Identifier as provided directly by the AF (in the case when the AF is within the operator’s domain).

The TSCTSF requests the Time Synchronization Subscription data from the UDM. The TSCTSF may also use stored Time Synchronization Subscription data which it retrieved from the UDM when the UE established PDU session, see clause 4.28.3.1.

5. The UDM provides the Nudm_SDM_Get response containing SUPI that are mapped from each received GPSI or a list of SUPIs mapped from the External/Internal Group Identifier and identify UEs targeted by the AF request.

6. (in the case of Ntsctsf_TimeSynchronization_CapsSubscribe): The TSCTSF uses the parameters received in step 3 and step 5 (i.e. DNN, S-NSSAI and the list of SUPIs if present) to find matching AF-session(s).

If the Time Synchronization Subscription data is available, the subscription data returned by the UDM includes the AF request authorization that indicates whether the AF is allowed to request (g)PTP-based time distribution for DNN/S-NSSAI. If the subscription data indicates that the AF is not allowed to request (g)PTP-based time synchronization, the AF-session is excluded from the list of matching AF-sessions.

For any such matching AF-session, the TSCTSF interacts with the PCF by triggering a Npcf_PolicyAuthorization_Update request message.

(in the case of Ntsctsf_TimeSynchronization_CapsUnsubscribe): The TSCTSF uses the Subscription Correlation ID to determine the AF sessions and interacts with the PCF(s) by triggering a Npcf_PolicyAuthorization_Delete request message. Steps 10-15 are skipped.

7. TSCTSF acknowledges the execution of Ntsctsf_TimeSynchronization_CapsSubscribe to the requester that initiated the request. The acknowledgement contains a Subscription Correlation ID that the requester can use to cancel or modify the subscription.

8. NEF acknowledges the execution of Nnef_TimeSynchronization_CapsSubscribe to the requester that initiated the request. The acknowledgement contains a Subscription Correlation ID that the AF can use to cancel or modify the subscription.

9. As part of Npcf_PolicyAuthorization_Update request, the TSCTSF uses the procedures as described in clause K.2.1 of TS 23.501 [2] to determine the (g)PTP capabilities from the DS-TT. If the TSCTSF has not determined the (g)PTP capabilities from the NW-TT, the TSCTSF determines the capabilities using the procedures as described in clause K.2.1 of TS 23.501 [2].

The TSCTSF composes the time synchronization capabilities for the DS-TT/UE(s) connected to the NW-TT based on the capability information received from the DS-TT(s) and NW-TT. If the Ntsctsf_TimeSynchronization_CapsSubscribe request include an Event Filter with one or more of the requested PTP instance type, requested transport protocol for PTP, or requested PTP Profile, the TSCTSF considers only the DS-TT(s) and NW-TT(s) with these capabilities as part of the time synchronization capability set that is reported to the NEF (or AF).

The TSCTSF maintains association between the user-plane Node ID, the time synchronization capabilities, the reference to the capabilities (as identified by the Subscription Correlation ID), the Event Filter (if available), the NEF or AF Notification Target Address and list of the AF sessions with PCFs with this user-plane Node ID. If the Ntsctsf_TimeSynchronization_CapsSubscribe request includes one or more Event Filter(s), the TSCTSF considers only the matching UE identities and the DS-TT(s) and NW-TT(s) with the matching capabilities to be included in the associated AF sessions.

10. The TSCTSF sends Ntsctsf_TimeSynchronization_CapsNotify (as described in clause 5.2.27.2.8) to the NEF. The message includes the time synchronization capabilities as composed in step 9. The message contains one or more user-plane Node ID(s) and a list of UE identities associated to each user-plane Node ID and time synchronization capabilities for each set of DS-TTs connected to given user-plane Node ID, as described in Table 5.2.6.25.8-1. The user-plane Node ID identifies the NW-TT to where the UE/DS-TT(s) are connected to.

11. The NEF sends Nnef_TimeSynchronization_CapsNotify with Time Synchronization capability event (as described in Table 5.2.6.25.8-1) to the AF.

12-13. Upon PDU Session Establishment as defined clause 4.3.2.2.1, steps 1, 9, 10 and 11 are repeated for the new PDU Session.

14. If necessary, e.g. upon PDU Session establishment or release, the TSCTSF may update the time synchronization capabilities for the DS-TT/UE(s) connected to the NW-TT(s). The TSCTSF sends Ntsctsf_TimeSynchronization_CapsNotify with Time Synchronization capability event (as described in Table 5.2.6.25.8-1) containing the updated capabilities to the NEF.

15. The NEF sends Nnef_TimeSynchronization_CapsNotify containing the updated capabilities to the AF.

4.15.9.3 Time Synchronization activation, modification and deactivation

4.15.9.3.1 General

This procedure can be used by the AF to activate, modify or deactivate the (g)PTP instances in 5GS.

The AF may activate the time synchronization service using the Nnef_TimeSynchronization_ConfigCreate service operation. The service operation creates a time synchronization configuration based on the service parameters as indicated in the create request. The AF may update the time synchronization configuration using the Nnef_TimeSynchronization_ConfigUpdate service operation. The AF may deactivate the time synchronization service using the Nnef_TimeSynchronization_ConfigDelete service operation, which deletes the corresponding time synchronization service configuration.

The Nnef_TimeSynchronization_ConfigCreate and Nnef_TimeSynchronization_ConfigUpdate request may contain the parameters as described in Table 4.15.9.3-1.

Table 4.15.9.3-1: Description of Time Synchronization service parameters

Time Synchronization Parameter	Description
PTP instance type	Identifies the requested PTP instance type as described in clause 5.27.1.4 of TS 23.501 [2].
Transport protocol	Identifies the requested transport protocol for PTP instance as described in clause 5.27.1.4 of TS 23.501 [2]. This is applicable for IEEE Std 1588 [76] Boundary Clock and Transparent Clock operation.
PTP Profile	Identifies the PTP profile for the PTP instance as requested by AF.
Grandmaster enabled	Indicates whether the AF requests the PTP instance in 5GS to be able to act as a grandmaster for PTP or gPTP (depending on the requested PTP instance type). This is applicable for IEEE Std 1588 [76] Boundary Clock or IEEE Std 802.1AS [75] operation. [optional]
Grandmaster priority	Indicates a priority used as defaultDS.priority1 when generating Announce message when 5GS acts as (g)PTP GM. Applicable only if the Grandmaster enabled = TRUE. If omitted, the default value as described in the PTP Profile is used. [optional]
Time Domain	(g)PTP domain of the PTP instance as defined in IEEE Std 1588 [76].
Temporal Validity Condition	Indicates start-time and stop-time attributes that describe the time period when the time synchronization service for a PTP instance is active. [optional]
Spatial Validity Condition	Indicates a geographical area (e.g., a civic address or shapes) or a TA list in which time synchronization service is enabled. [optional]
Time synchronization error budget	Indicates the time synchronization budget for the time synchronization service (as described in clause 5.27.1.9 of TS 23.501 [2]). [optional]
For each PTP port in the PTP instance
Either UE identity (for a DS-TT port), or "N6 interface" indication	Identifies the UE/DS-TT which the parameters below apply. "N6 interface" indicates that the parameters below apply to the N6 interface. If the "PTP port" needs to be identified, this field refers to the UE identity (GPSI or SUPI). If the N6 termination needs to be identified, then this field indicates "N6 interface" flag, instead of SUPI or GPSI.
PTP enabled	TRUE/FALSE. This is used to set the portDS.portEnable. If omitted, the default value as described in the PTP Profile is used. [optional]
Log Sync Interval	Specifies the mean time interval between successive Sync messages. This is applicable for IEEE Std 1588 [76] Boundary Clock or IEEE Std 802.1AS [75] operation. If omitted, the default value as described in the PTP Profile is used. [optional]
Use management settable Log Sync Interval	TRUE/FALSE. This is applicable if the PTP Profile is I IEEE Std 802.1AS [75]. When set to FALSE, the Log Sync Interval is used to set the initialLogSyncInterval as described in IEEE Std 802.1AS [75]. When set to TRUE, the Log Sync Interval is used to set the mgtSettableLogSyncInterval as described in IEEE Std 802.1AS [75]. If omitted, the default value as described in the IEEE Std 802.1AS [75] is used. [optional]
Log Announce Interval	Specifies the mean time interval between successive Announce messages. This is applicable for IEEE Std 1588 [76] Boundary Clock or IEEE Std 802.1AS [75] operation. If omitted, the default value as described in the PTP Profile is used. [optional]
Use management settable Log Announce Interval	TRUE/FALSE. This is applicable if the PTP Profile is IEEE Std 802.1AS [75]. When set to FALSE, the Log Announce Interval is used to set the initialLogAnnounceInterval as described in IEEE 802.1AS. When set to TRUE, the Log Announce Interval is used to set the mgtSettableLogAnnounceInterval as described in IEEE Std 802.1AS [75]. If omitted, the default value as described in the IEEE Std 802.1AS [75] is used. [optional]

The AF may use Nnef_TimeSynchronization_CapsSubscribe service operation as described in clause 4.15.9.2 to learn the UE capabilities for time synchronization service. The Nnef_TimeSynchronization_CapsNotify service operation indicates the list of UE identities, User-plane Node ID and the Subscription Correlation ID. The AF can use the Subscription Correlation ID and the user-plane node ID received in the Nnef_TimeSynchronization_CapsNotify service operation as a target of the Nnef_TimeSynchronization_ConfigCreate request. The NEF uses the Subscription Correlation ID and user-plane node ID to determine the list of UEs and list of AF-sessions to which the Nnef_TimeSynchronization_ConfigCreate service operation is targeted to.

4.15.9.3.2 Time synchronization service activation

Figure 4.15.9.3.2-1: Time synchronization service activation

1. The AF creates a time synchronization service configuration for a PTP instance by invoking Nnef_TimeSynchronization_ConfigCreate service operation. The request includes the parameters as described in Table 4.15.9.3-1. The request contains a Subscription Correlation ID and user-plane node ID as a reference to the target of the UEs and AF-sessions.

The create request creates also a subscription for the changes in the time synchronization service configuration.

2. The NEF authorizes the request. After successful authorization, the NEF invokes the Ntsctsf_TimeSynchronization_ConfigCreate service operation with the corresponding TSCTSF, with the parameters as received from the AF.

If the request includes a spatial validity condition and if the AF uses a geographical area as a spatial validity condition, the NEF transforms this information into 3GPP identifiers (e.g. TAI(s)) based on pre-configuration.

The AF that is part of operator’s trust domain may invoke the services directly with TSCTSF.

If the request includes a spatial validity condition and if the AF is within the operator’s domain, the spatial validity condition shall comprise of a list of TA(s).

3. TSCTSF checks with the UDM if the UE is allowed to receive the time sync service. The TSCTSF responds with the Ntsctsf_TimeSynchronization_ConfigCreate response. The Ntsctsf_TimeSynchronization_ConfigCreate response includes a PTP instance reference.

4. The NEF responds with the Nnef_TimeSynchronization_ConfigCreate response, including a reference to the time synchronization service configuration (PTP instance reference).

5-6. The TSCTSF uses the Subscription Correlation ID and user-plane node ID in Ntsctsf_TimeSynchronization_ConfigCreate to determine the target UEs and corresponding AF-sessions. The TSCTSF uses the parameters (e.g. requested PTP instance type, transport protocol and PTP profile) in the Ntsctsf_TimeSynchronization_ConfigCreate request to determine suitable DS-TT(s) and corresponding AF-sessions among all AF-sessions that are associated with the Subscription Correlation ID and user-plane node ID in the request.

The TSCTSF maintains association between list of suitable AF-sessions, corresponding time synchronization configuration, the PTP instance reference in 5GS, PTP instance references in each involved DS-TT and NW-TT and Subscription Correlation ID and user-plane node ID as given in step 1.

NOTE 1: The AF-sessions that are not associated with a time synchronization configuration, are available to be selected as suitable AF-sessions in another Ntsctsf_TimeSynchronization_ConfigCreate request.

The TSCTSF uses the procedures described in clause K.2.2 of TS 23.501 [2] to configure and initialize the PTP instance in the DS-TT(s) and NW-TT. The TSCTSF constructs a PMIC to each DS-TT/UE to activate the time synchronization service in DS-TT in respect to the service parameters in the request in step 2. The TSCTSF constructs PMIC(s) and UMIC to NW-TT to activate the time synchronization service in NW-TT in respect to the service parameters in the request in step 2.

Upon reception of responses from each DS-TT and NW-TT, the TSCTSF determines the state of the time synchronization configuration.

The TSCTSF constructs a PMIC to each DS-TT/UE to subscribe for the port management information changes in the DS-TT. The TSCTSF constructs PMIC(s) and UMIC to NW-TT to subscribe for the port management and user-plane management information changes in NW-TT. The TSCTSF retrieves the PMIC(s) and UMIC via means of Npcf_PolicyAuthorization service operations.

The create request creates also a subscription for notifications for the changes in the time synchronization service configuration.

If the Ntsctsf_TimeSynchronization_ConfigCreate request contains a temporal validity condition with a start-time and/or the stop-time that is in the future, the TSCTSF maintains the start-time and stop-time for the time synchronization service for the corresponding time synchronization configuration. If the start-time is in the past, the TSCTSF treats the request as if the time synchronization service was activated immediately. When the start-time is reached, the TSCTSF proceeds as described in this step above. When the stop-time is reached for active time synchronization service configuration, the TSCTSF proceeds as Ntsctsf_TimeSynchronization_ConfigDelete was received as described in clause 4.15.9.3.4.

If the Ntsctsf_TimeSynchronization_ConfigCreate request contains a spatial validity condition, then the TSCTSF performs the following operations:

– For each target UE, TSCTSF determines whether the TSCTSF has subscribed for the UE presence in Area of Interest composed by the TA(s) in the spatial validity condition. If not, the TSCTSF discovers the AMF(s) serving TAs that comprise the spatial validity condition, using the NRF discovery service (Nnrf_NFDiscovery_Request) with the list of TA(s). Then the TSCTSF subscribes to the AMF(s) to receive notifications about the UE presence in Area of Interest using Namf_EventExposure operation with the corresponding event filters as described in clause 5.2.2.3. The subscribed area of interest may be the same as the spatial validity condition or may be a subset of the spatial validity condition (e.g. a list of TAs) based on the latest known UE location.

– Based on the notification from the AMF and spatial validity condition received in step 1, the TSCTSF determines whether to activate time synchronization service for this UE:

– If the UE location is within the spatial validity condition, the TSCTSF determines to activate time synchronization service for the UE/DS-TT creating the PTP port in DS-TT and adding it to the PTP instance. The TSCTSF uses the procedures described in clause K.2.2 of TS 23.501 [2] to configure and initialize the PTP instance in the DS-TT(s) and NW-TT.

– If the UE location is outside the spatial validity condition, the TSCTSF determines not to activate time synchronization service and not to create a PTP port in a DS-TT.

The TSCTSF uses the procedure in clause 4.15.9.4 to activate or modify the 5G access stratum time distribution for the UEs that are part of the impacted PTP instance.

7. The TSCTSF notifies the NEF (or AF) with the Ntsctsf_TimeSynchronization_ConfigUpdateNotify service operation, containing the PTP instance reference and the current state of the time synchronization service configuration.

If TSCTSF received spatial validity condition as part of the Ntsctsf_TimeSynchronization_ConfigCreate request, the TSCTSF notifies the NEF (or AF) with the Ntsctsf_TimeSynchronization_ConfigUpdateNotify service operation, whenever the UE moves in or out of the Area of Interest. The notification contains the PTP instance reference and the current state of the time synchronization service configuration.

8. The NEF notifies the AF with the Nnef_TimeSynchronization_ConfigUpdateNotify service operation, containing the PTP instance reference and the current state of the time synchronization service configuration.

9. Upon a change in the PTP instance in the DS-TT or NW-TT, the DS-TT or NW-TT report the change via PMIC or UMIC to the TSCTSF as described in clause K.2.2 of TS 23.501 [2].

Upon PDU Session release indication from a PCF, the TSCTSF removes the corresponding AF-session from the list of AF-sessions associated with the time synchronization configuration. The TSCTSF uses the procedure in clause 4.15.9.4 to remove the 5G access stratum time distribution parameters for the UE that is removed from the impacted PTP instance.

Upon PDU Session Establishment as defined clause 4.3.2.2.1, steps 10-13 in Figure 4.15.9.2-1 are repeated for the new PDU Session and the TSCTSF may notify the NEF (or AF) for the Time Synchronization capability event, optionally with the updated time synchronization capabilities, as described in step 12 in Figure 4.15.9.2-1.

NOTE 2: Upon receiving the notification, the NEF (or AF) can use the Ntsctsf_TimeSynchronization_ConfigUpdate service operation to add the DS-TT/UE to the existing PTP instance and corresponding time synchronization service configuration.

If TSCTSF received spatial validity condition as part of the Ntsctsf_TimeSynchronization_ConfigCreate request, upon a change in the UE presence in Area of Interest, the TSCTSF determines if the spatial validity condition shall trigger an activation or deactivation of the time synchronization service:

– If the UE has moved outside the spatial validity condition, then the TSCTSF temporarily removes the UE/DS-TT port from the PTP instance:

– If the DS-TT is configured to send Sync, Follow_Up and Announce messages for the related PTP instance, then TSCTSF deactivates the Grandmaster functionality in the DS-TT using PMIC (see also clause K.2.2.4 of TS 23.501 [2]).

– If NW-TT is configured to send Sync, Follow_Up and Announce messages on behalf of the DS-TT, then TSCTSF deactivates the Grandmaster functionality on behalf of the DS-TT in NW-TT using UMIC (see also clause K.2.2.4 of TS 23.501 [2]).

– If the UE has moved inside the spatial validity condition, then the TSCTSF adds the DS-TT PTP port to the PTP instance and also (re-)activates the Grandmaster functionality (described in clause K.2.2 of TS 23.501 [2]).

10. The TSCTSF updates the state of the time synchronization configuration and may notify the NEF (or AF) with the Ntsctsf_TimeSynchronization_ConfigUpdateNotify service operation, containing the PTP instance reference and the updated state of the time synchronization service configuration, including whether there was a change in the UE’s presence in the spatial validity condition (in cases when the AF has requested the service for a specific spatial validity condition).

11. The NEF notifies the AF with the Nnef_TimeSynchronization_ConfigUpdateNotify service operation, containing the reference to the time synchronization service configuration (PTP instance reference) and the updated state of the time synchronization service configuration.

4.15.9.3.3 Time synchronization service modification

Figure 4.15.9.3.3-1: Time synchronization service modification

1. To update an existing time synchronization service configuration of the PTP instance, the AF invokes a Nnef_TimeSynchronization_ConfigUpdate service operation providing the corresponding PTP instance reference.

2. The NEF invokes the Ntsctsf_TimeSynchronization_ConfigUpdate service operation with the corresponding TSCTSF.

The AF that is part of the operator’s trust domain may invoke the services directly with the TSCTSF.

3. If the update request includes changes in the Spatial validity condition, the TSCTSF determines the UE’s presence in the updated Spatial validity condition as specified in steps 3-7 of the time synchronization activation procedure in clause 4.15.9.3.2.

4. The TSCTSF responds with the Ntsctsf_TimeSynchronization_ConfigUpdate response where the AF may include an indication that the UE(s) are (not) present in the Requested Coverage Area (in cases when the AF has requested the service for a specific area).

5. The NEF responds with the Nnef_TimeSynchronization_ConfigUpdate.

6-7. The TSCTSF uses the PTP instance reference included in the Ntsctsf_TimeSynchronization_ConfigUpdate request to identify the time synchronization service configuration and the corresponding AF sessions.

If the Ntsctsf_TimeSynchronization_ConfigUpdate request includes updated service parameters for the PTP instance and if the corresponding DS-TT(s) and NW-TT are suitable with the parameters (e.g. requested PTP instance type, transport protocol and PTP profile), the TSCTSF uses the procedures described in clause K.2.2 of TS 23.501 [2] to update the PTP instance(s) in the DS-TT(s) and NW-TT.

If the Ntsctsf_TimeSynchronization_ConfigUpdate request includes one or more UE identities to be added to the PTP instance, if the corresponding DS-TT(s) are suitable with the parameters (e.g. requested PTP instance type, transport protocol and PTP profile) in the time synchronization service configuration as identified by the PTP instance reference in the request:

– the TSCTSF adds the suitable AF-sessions to the list of AF-sessions that are associated with the time synchronization service configuration; and

– the TSCTSF uses the procedures described in clause K.2.2 of TS 23.501 [2] to initialize and activate the PTP instance(s) in the corresponding DS-TT(s).

– the TSCTSF uses the procedure in clause 4.15.9.4 to modify or activate the 5G access stratum time distribution for the UEs that are added to the impacted PTP instance.

If the Ntsctsf_TimeSynchronization_ConfigUpdate request includes one or more UE identities to be removed to the PTP instance, the TSCTSF removes the corresponding AF-sessions from the list of AF-sessions associated with the time synchronization configuration. The TSCTSF uses the procedure in clause 4.15.9.4 to remove the 5G access stratum time distribution parameters for the UEs that are removed from the impacted PTP instance.

8. The TSCTSF notifies the NEF (or AF) with the Ntsctsf_TimeSynchronization_ConfigUpdateNotify service operation, containing the PTP instance reference and the current state of the time synchronization service configuration, including and whether there was a change in the UE’s presence in the Spatial validity condition (in cases when the AF has requested the service for a specific area).

9. The NEF notifies the AF with the Nnef_TimeSynchronization_ConfigUpdateNotify service operation, containing the PTP instance reference and the current state of the time synchronization service configuration.

4.15.9.3.4 Time synchronization service deactivation

Figure 4.15.9.3.4-1: Time synchronization service deactivation

1. To remove an existing time synchronization service configuration of the PTP instance, the AF invokes a Nnef_TimeSynchronization_ConfigDelete service operation providing the corresponding PTP instance reference.

2. The NEF invokes the Ntsctsf_TimeSynchronization_ConfigDelete service operation with the corresponding TSCTSF.

The AF that is part of operator’s trust domain may invoke the services directly with TSCTSF.

The TSCTSF may also invoke the Ntsctsf_TimeSynchronization_ConfigDelete service operation when it determines (based on notifications from the AMF(s), see steps 3-7 of clause 4.15.9.3.2) that the UE(s) are outside the Spatial validity condition.

3. The TSCTSF responds with the Ntsctsf_TimeSynchronization_ConfigDelete response.

4. The NEF responds with the Nnef_TimeSynchronization_ConfigDelete response.

5-6. The TSCTSF uses the PTP instance reference included in the Ntsctsf_TimeSynchronization_ConfigDelete request to identify the time synchronization service configuration and the corresponding AF sessions. The TSCTSF uses the procedures described in clause K.2.2 of TS 23.501 [2] to disable the corresponding PTP instance(s) in the DS-TT(s) and NW-TT. The TSCTSF deletes the time synchronization service configuration for the respective PTP instance.

The TSCTSF uses the procedure in clause 4.15.9.4 to deactivate the 5G access stratum time distribution for the UEs that are part of the impacted PTP instance.

4.15.9.4 Procedures for management of 5G access stratum time distribution

The AF can use the procedure to activate, update or delete the 5G access stratum time distribution for one UE or a group of UEs.

The AF may query the status of the 5G access stratum time distribution using Nnef_ASTI_Get service operation. The Nnef_ASTI_Create and Nnef_ASTI_Update request may contain the parameters as described in Table 4.15.9.4-1.

Table 4.15.9.4-1: Description of 5G access stratum time distribution parameters

Parameter	Description
5G access stratum time distribution indication (enable, disable)	Indicates that the access stratum time distribution via Uu reference point should be activated or deactivated for the associated UE identities.
Time synchronization error budget	Indicates the time synchronization error budget for the time synchronization service (as described in clause 5.27.1.9 of TS 23.501 [2]). [optional]
Temporal Validity Condition	Indicates start-time and stop-time attributes that describe the time period when the time synchronization service is active. [optional]
Spatial Validity Condition	Indicates a geographical area (e.g., a civic address or shapes) or a TA list in which time synchronization service is enabled. [optional]

Figure 4.15.9.4-1: Management of 5G access stratum time information

1. AM Policy Association establishment as described in clause 4.16.1.

2. (When the procedure is triggered by the AF request to influence the 5G access stratum time distribution):

– To create a new request, the AF provides access stratum time distribution parameters to the NEF using the Nnef_ASTI_Create service operation (together with the AF identifier and potentially further inputs as specified in table 4.15.9.4-1), including a target (one UE identified by SUPI or GPSI, a group of UEs identified by an External Group Identifier. The NEF forwards the GPSI or the External Group Identifier to the TSCTSF by including it inside the Ntsctsf_ASTI_Create request.

– To update or remove an existing request, the AF invokes an Nnef_ASTI_Update or Nnef_ASTI_Delete service operation providing the corresponding time synchronization configuration id.

– To query the status of the access stratum time distribution, the AF invokes Nnef_ASTI_Get service operation providing the target (a list of UE identities (SUPI or GPSIs) or an External Group Identifier).

The AF that is part of operator’s trust domain may invoke the services directly with the TSCTSF and identifies the targeted UE(s) using SUPI(s) or an Internal Group Identifier.

If the request includes a spatial validity condition and the AF uses a geographical area as a spatial validity condition, the NEF transforms this information into 3GPP identifiers (e.g. TAI(s)) based on pre-configuration.

NOTE 1: Steps 1 and 2 can occur in any order.

3. (When the procedure is triggered by the AF request to influence the 5G access stratum time distribution):

– The NEF authorizes the request. After successful authorization, the NEF invokes the Ntsctsf_ASTI_Create/Update/Delete/Get service operation with the TSCTSF discovered and selected as described in clause 6.3.24 of TS 23.501 [2].

– The TSCTSF determines whether the targeted UE is part of a PTP instance in 5GS, if so the TSCTSF rejects the request (steps 4-10 are skipped).

– The TSCTSF calculates the Uu time synchronization error budget as described in clause 5.27.1.9 of TS 23.501 [2]. This does not apply in case of Ntsctsf_ASTI_Delete service operation.

(When the procedure is triggered by PTP instance activation, modification, or deactivation in the TSCTSF):

– The TSCTSF calculates the Uu time synchronization error budget as described in clause 5.27.1.9 of TS 23.501 [2] for corresponding SUPIs that are part of the PTP instance. This does not apply in case of Ntsctsf_ASTI_Delete service operation.

4. If the AF targeted UE(s) are identified by GPSI(s) or an External/Internal Group Identifier, the TSCTSF uses the Nudm_SDM_Get request to retrieve the subscription information (SUPI(s)) from the UDM using each GPSI or the External Group Identifier as received from the NEF, or an Internal Group Identifier as provided by the AF directly.

5. The UDM provides the Nudm_SDM_Get response containing SUPI(s) that are mapped from each received GPSI or the External/Internal Group Identifier and identify the targeted UEs.

6a. If the Ntsctsf_ASTI_Create request in step 2 contains a spatial validity condition, then the TSCTSF performs the following operations:

– For each target UE, TSCTSF determines whether the TSCTSF has subscribed for the UE presence in Area of Interest composed by the TAs list in the spatial validity condition. If not, the TSCTSF discovers the AMF(s), serving in the TAs that comprise the spatial validity condition, using the NRF discovery service (Nnrf_NFDiscovery_Request) with the list of TAs. Then the TSCTSF subscribes to the AMF(s) to receive notifications about the UE presence in Area of Interest using Namf_EventExposure operation with the corresponding event filters as described in clause 5.2.2.3. The subscribed area of interest may be the same as the spatial validity condition or may be a subset of the spatial validity condition (e.g. a list of TAs) based on the latest known UE location.

– Based on the notification from the AMF and spatial validity condition received in step 1, the TSCTSF determines whether to activate time synchronization service for this UE:

– If the UE location is within the spatial validity condition, the TSCTSF determines to enable access stratum time distribution for the UE.

– If the UE location is outside the spatial validity condition, the TSCTSF determines to disable access stratum time distribution for the UE.

6b. If for any targeted UE, the "AF request Authorization" in the Time Synchronization Subscription Data indicates that the AF is allowed to request 5G access stratum-based time distribution, the TSCTSF proceeds with ASTI service configuration. Otherwise, if the AF is not authorized, steps 7-11 are skipped for this UE.

7. The TSCTSF searches the PCF for the UE using Nbsf_Management_Subscribe with a SUPI as an input parameter, indicating that it is searching for the PCF that handles the AM Policy Association of the UE.

8. The BSF provides to the TSCTSF the identity of the PCF for the UE for the requested SUPI via an Nbsf_Management_Notify operation. If matching entries already existed in the BSF when step 6 is performed, this shall be immediately reported to the TSCTSF.

9. The TSCTSF sends to the PCF for the UE its request for the AM policy of the UE (identified by SUPI) using Npcf_AMPolicyAuthorization request, containing the 5G access stratum time distribution indication (enable, disable) and optionally the calculated Uu time synchronization error budget.

10. If the PCF receives multiple time synchronization error budgets for a given UE, then the PCF picks the most stringent budget. The PCF takes a policy decision and then the PCF may initiate an AM Policy Association Modification procedure for the UE as described in clause 4.16.2.2 to provide AMF the 5G access stratum time distribution parameters. As part of this, the AMF shall, if supported, store the 5G access stratum time distribution indication (enable, disable) and the Uu time synchronization error budget in the UE context in AMF and send the 5G access stratum time distribution indication (enable, disable) and the Uu time synchronization error budget, when they are available, to NG-RAN during mobility registration, AM policy modification, Service Request, N2 Handover and Xn handover as specified in TS 38.413 [10]. The NG-RAN node shall, if supported, store the information in the UE Context. Based on this information, the NG-RAN node provides the 5GS access stratum time to the UE according to the Uu time synchronization error budget as provided by the TSCTSF (if supported by UE and NG-RAN).

NOTE 2: This release of the specification assumes that deployments ensure that the targeted UEs and the NG-RAN nodes serving those UEs support Rel-17 propagation delay compensation as defined in TS 38.300 [30].

11. The PCF of the UE replies to the TSCTSF with the result of Npcf_AMPolicyAuthorization operation.

12. The TSCTSF responds the AF with the Ntsctsf_ASTI_Create/Update/Delete/Get service operation response.

13. The NEF informs the AF about the result of the Nnef_ASTI_Create/Update/Delete/Get service operation performed in step 2.

14. If TSCTSF received spatial validity condition as part of the Ntsctsf_ASTI_Create request in step 2, upon the reception of a change in the UE presence in Area of Interest notification, the TSCTSF determines if the spatial validity condition shall trigger an activation or deactivation of the access stratum time distribution:

– If the UE has moved inside the spatial validity condition, then the TSCTSF determines to enable access stratum time distribution for the UE.

– If the UE has moved outside the spatial validity condition, then the TSCTSF determines to disable access stratum time distribution for the UE.

15-16. If TSCTSF determines to modify access stratum time distribution for the UE in step 14 for which the AF requested access stratum time distribution, the TSCTSF notifies the service status to AF.