6.1B Transfer of analytics context and analytics subscription

23.2883GPPArchitecture enhancements for 5G System (5GS) to support network data analytics servicesRelease 18TS

6.1B.1 General

In a multiple NWDAFs deployment scenario, procedures for transfer of analytics context and analytics subscription can be used to support the target NWDAF to produce the needed analytics.

When the analytics consumer provides the target NWDAF with information on the subscription that could be transferred from the source NWDAF, the target NWDAF may initiate the transfer of analytics context. The analytics consumer provides the information via Nnwdaf_AnalyticsSubscription_Subscribe service operation. When the analytics consumer is an AMF, the old subscription information (if related to a UE) may be provided by the source AMF to the target AMF using a UE context transfer procedure as specified in TS 23.502 [3].

An analytics subscription transfer to the target NWDAF may be initiated by the source NWDAF, followed by an analytics context transfer initiated by the target NWDAF. An NWDAF may transfer one or more of its analytics subscriptions to another NWDAF instance due to internal (e.g. load balancing, graceful shutdown) or external triggers (e.g. UE mobility). For external triggers, the NWDAF may subscribe to NF(s) to be notified about the corresponding events. As for UE mobility, upon the UE location change event notified by the AMF subscribed by the NWDAF, the NWDAF determines whether it can continue to provide the analytics service. If the NWDAF cannot continue to serve the consumer, it should either select a target NWDAF and initiate analytics subscription transfer, or notify the analytics consumer that it cannot provide the service anymore, so that the analytics consumer can select a new NWDAF.

Procedures for analytics subscription transfer allow one NWDAF instance to transfer its ongoing analytics subscriptions to another NWDAF instance. The transfer can be done for all subscriptions or just a selected subset of subscriptions related to specific area(s), specific Analytics ID(s), specific NF(s) and/or specific UE(s).

The procedure for prepared analytics subscription transfer can be used if the source NWDAF instance anticipates that it will soon not be able to continue its current analytics tasks.

6.1B.2 Analytics Transfer Procedures

6.1B.2.1 Analytics context transfer initiated by target NWDAF selected by the NWDAF service consumer

The procedure in Figure 6.1B.2.1-1 is used when an NF decides to select a new NWDAF instance due to internal or external triggers, e.g. the NF starts serving a UE with analytics subscription information received upon UE context transfer procedure as described in TS 23.502 [3], or the NF starts to request NF related analytics, or the NF receives a "Termination Request" for an existing analytics subscription from an NWDAF. The NF sends to the target NWDAF information about the NWDAF previously used for analytics subscription, if available, in Nnwdaf_AnalyticsSubscription_Subscribe service operation. The target NWDAF may initiate the transfer of the analytics context, using the Nnwdaf_AnalyticsInfo_ContextTransfer or Nnf_DataManagement_Subscribe service operation.

The procedure in Figure 6.1B.2.1-1 is also used when an Aggregator NWDAF decides to select a new NWDAF to request output analytics for analytics aggregation. For example, upon receiving a Termination Request from one of the NWDAFs that are collectively serving a request for analytics subscription as specified in clause 6.1A, the Aggregator NWDAF queries the NRF or UDM to select a target NWDAF as specified in clause 6.1A.3 using information e.g. the UE location, the 5GC NFs (identified by their NF Set IDs or NF types) serving the UE or to be contacted for data collection (if Area of Interest is not provisioned for the requested analytics), or the subset of AoI (if Area of Interest is provisioned for the requested analytics). Then, the Aggregator NWDAF sends information about the NWDAF previously used for analytics subscription, if available, in Nnwdaf_AnalyticsSubscription_Subscribe service operation towards the selected target NWDAF.

Figure 6.1B.2.1-1: Analytics context transfer initiated by target NWDAF selected by the NWDAF service consumer

1. The NWDAF service consumer determines to select an NWDAF instance. The consumer discovers and selects the target NWDAF as specified in clause 5.2.

2. The consumer sends a request for analytics subscription to the target NWDAF using Nnwdaf_AnalyticsSubscription_Subscribe service operation, including information on the previous analytics subscription (i.e. NWDAF ID, Analytics ID(s), SUPIs, Analytics Filter Information for UE-related Analytics and Subscription Correlation ID) which relates to the requested analytics subscription, if available. If the target NWDAF accepts the analytics subscription request, it sends Nnwdaf_AnalyticsSubscription_Subscribe response with a Subscription Correlation ID.

If the target NWDAF does not receive information of previous analytics subscription in step 2, for UE related Analytics, the target NWDAF may discover previously used NWDAF in UDM as specified in clause 5.2.

NOTE 1: If the selected target NWDAF instance is the same as the source NWDAF instance (as received from the other consumer in step 0), the target NWDAF will update the existing analytics subscription to the new analytics consumer. Following steps are skipped.

NOTE 2: The consumer can provide information on the previous analytics subscription when, e.g. the consumer is an AMF and it received information from the old AMF, see clause 5.2.2.2.2 of TS 23.502 [3].

3a. [Option 1] If the target NWDAF decides to request an analytics context transfer from the previously used NWDAF, it may make use of information sent in step 2 (e.g. the provided Subscription Correlation ID) and use the analytics context transfer procedure as specified in clause 6.1B.3. The target NWDAF may receive an ADRF ID or DCCF ID for collecting the historical data and/or analytics.

3b-c. [Option 2] If the target NWDAF decides to only request historical data and/or analytics, then it may collect the data and/or analytics via Nnf_DataManagement_Subscribe service, where the NFs may be either the ADRF, NWDAF or DCCF, as described in clauses 10.2.6, 7.4.2 and 8.2.2 respectively.

Target NWDAF is now ready to generate analytics information taking into account the information received in step 3.

4. [Optional] Source NWDAF may purge analytics context after completion of step 3a, if performed and if not already done, unsubscribes from the data source(s) and/or model source(s) that are no longer needed for the remaining analytics subscriptions.

5. [Optional] Target NWDAF may subscribe to relevant data source(s) and/or model source(s), if it is not yet subscribed to the data source(s) and/or model source(s).

6.1B.2.2 Analytics Subscription Transfer initiated by source NWDAF

The procedure in Figure 6.1B.2.2-1 is used by an NWDAF instance to request the transfer of analytics subscription(s) to another NWDAF instance, using the Nnwdaf_AnalyticsSubscription_Transfer service operation defined in clause 7.2.5.

If the source NWDAF discovers that the analytics consumer may change concurrently to this procedure, the source NWDAF should not perform the procedure. In such a case, the source NWDAF may send a message to indicate to the analytics consumer that it will not serve this subscription anymore.

NOTE 1: To discover the possible change of analytics consumer, if the Analytics ID is UE related, the source NWDAF takes actions responding to external trigger (such as UE mobility), for example, checking if the Target of Analytics Reporting is still within the serving area of the analytics consumer, if the serving area information is available.

NOTE 2: Handling of overload situation or preparation for a graceful shutdown are preferably executed inside an NWDAF Set, when available, therefore, not requiring an analytics subscription transfer as described in this clause. The procedure in Figure 6.1B.2.2-1 is applicable for analytics subscription transfer across NF Sets or if the NWDAF is not deployed in a Set.

Figure 6.1B.2.2-1: Analytics subscription transfer initiated by source NWDAF

0. The analytics consumer subscribes to analytics from source NWDAF. The analytics consumer may send its NF ID or serving area, enabling NWDAF to determine whether the following analytics subscription transfer procedure is applicable. Optionally the source NWDAF subscribes to UE mobility events.

1. [Optional] Source NWDAF determines, e.g. triggered by a UE mobility event notification, to prepare an analytics subscription transfer to target NWDAF(s), as specified in the procedure illustrated in clause 6.1B.2.3.

2. Source NWDAF determines, e.g. based on the UE location information received and the analytics consumer’s serving area either directly received in step 0 or indirectly received via NRF, to perform an analytics subscription transfer to target NWDAF(s). Therefore, the source NWDAF determines the analytics subscription(s) to be transferred to a target NWDAF.

3. Source NWDAF performs an NWDAF discovery and selects the target NWDAF. NWDAF discovery may be skipped if the target NWDAF had already been discovered as part of a prepared analytics subscription transfer. In the case of aggregated analytics from multiple NWDAFs, the source NWDAF may use the set of NWDAF identifiers related to aggregated analytics (see clause 6.1.3) to preferably select a target NWDAF that is already serving the consumer.

4. Source NWDAF requests, using Nnwdaf_AnalyticsSubscription_Transfer Request service operation, a transfer of the analytics subscription(s) determined in step 2 to the target NWDAF. The request contains a callback URI of the analytics consumer. The request may also contain active data source ID(s) and ML model related information, which are related to the analytics subscriptions requested to be transferred, if not already provided as part of the prepared analytics subscription transfer in the preparation procedure (see step 1). The ML model related information contains the ID(s) of NWDAF(s) containing MTLF that provided the trained models and may contain the file address(es) of the trained ML model(s), where the file address(es) of the trained ML model(s) is included only when the source NWDAF itself provides the trained ML model(s) for the analytics subscription(s) being transferred. The request message may also include "analytics context identifier(s)" indicating the availability of analytics context for particular Analytics ID(s).

5. Target NWDAF accepts the analytics subscription transfer and takes over the analytics generation based on the information received from the source NWDAF.

Target NWDAF may use the ML model related information, if provided in the Nnwdaf_AnalyticsSubscription_Transfer request. If the ID(s) of NWDAF(s) containing MTLF is provided in the Nnwdaf_AnalyticsSubscription_Transfer request and the NWDAF(s) containing MTLF is part of the locally configured set of NWDAFs containing MTLF, target NWDAF may request or subscribe to the ML model(s) from the indicated NWDAF(s) containing MTLF as specified in clause 6.2A and use the ML model(s) for the transferred analytics subscription. If the file address(es) of the trained ML model(s) is provided and if the NWDAF containing MTLF is part of the locally configured set of NWDAFs containing MTLF, the target NWDAF may retrieve the ML model using the file address of the trained ML model. If the provided ID(s) of NWDAF(s) containing MTLF are not part of the locally configured set of ID(s) of NWDAFs containing MTLF, the target NWDAF discovers the NWDAF(s) supporting MTLF that can provide trained ML model(s) for the Analytics ID(s) as described in clause 5.2.

NOTE 3: If not yet done during a prepared analytics subscription transfer, the target NWDAF allocates a new Subscription Correlation ID to the received analytics subscriptions.

NOTE 4: The target NWDAF might already have received information on some/all of the analytics subscriptions as part of the prepared analytics subscription transfer request received in step 1 and, thus, might already have started to prepare for the analytics generation, e.g. by having already subscribed to relevant event notifications.

6. Target NWDAF informs the analytics consumer about the successful analytics subscription transfer using a Nnwdaf_AnalyticsSubscription_Notify message. A new Subscription Correlation ID, which was assigned by the target NWDAF, is provided in the Subscription Correlation ID and the old Subscription Correlation Id, which was allocated by the source NWDAF, is provided in the Subscription Change Notification Correlation ID parameter of this message as specified in clause 7.2.4.

NOTE 5: Notification correlation information in the Nnwdaf_AnalyticsSubscription_Notify message allows the analytics consumer to correlate the notifications to the initial subscription request made with the source NWDAF in step 0.

NOTE 6: The existing Analytics context in the source NWDAF is not deleted directly but will be purged first when it was collected by the target NWDAF.

NOTE 7: If this subscription is used as input for analytics aggregation by the analytics consumer, the analytics consumer might inform the other NWDAFs instance participating in this analytics aggregation that the Set of NWDAF identifiers of NWDAF instances used by the NWDAF service consumer for this analytics aggregation (see clause 6.1.3) has changed using the Nnwdaf_AnalyticsSubscription_Subscribe service operation.

7. [Conditional] If "analytics context identifier(s)" had been included in the Nnwdaf_AnalyticsSubscription_Transfer Request received in step 4, the target NWDAF requests the "analytics context". The analytics context transfer procedure is specified in clause 6.1B.3.

8. [Optional] Target NWDAF subscribes to relevant data source(s), if it is not yet subscribed to the data source(s) for the data required for the Analytics.

9. Target NWDAF confirms the analytics subscription transfer to the source NWDAF.

10. [Optional] Source NWDAF unsubscribes with the data source(s) that are no longer needed for the remaining analytics subscriptions. In addition, Source NWDAF unsubscribes with the NWDAF(s) containing MTLF, if exist, which are no longer needed for the remaining analytics subscriptions.

NOTE 8: At this point, the analytics subscription transfer is deemed completed, i.e. the source NWDAF can delete all information related to the successfully transferred analytics subscription.

11-12. Target NWDAF at some point derives new output analytics based on new input data and notifies the analytics consumer about the new analytics using a Nnwdaf_AnalyticsSubscription_Notify message as specified in clause 6.1.1.

6.1B.2.3 Prepared analytics subscription transfer

The procedure in Figure 6.1B.2.3-1 is used by an NWDAF instance to request another NWDAF instance for a prepared analytics subscription transfer from the source NWDAF instance, using the Nnwdaf_AnalyticsSubscription_Transfer service operation defined in clause 7.2.5.

NOTE 1: The source NWDAF might determine that it needs to prepare to transfer analytics to another NWDAF instance, e.g. when the source NWDAF estimates for UE related analytics subscription that the UE might enter an area which is not covered by the source NWDAF (e.g. by subscribing to AMF event exposure service for UE mobility event notifications, by performing UE mobility analytics, or by subscribing to another NWDAF providing UE mobility analytics). If the source NWDAF discovers that the analytics consumer may change concurrently to this procedure, the source NWDAF does not perform the procedure. If the procedure makes use of predictions to determine the candidate NWDAFs, care must be taken with regards to load and signalling cost when sending data to an NWDAF that will not eventually start serving the UE.

NOTE 2: The source NWDAF might also determine that it needs to prepare to transfer analytics subscriptions to another NWDAF instance, as the source NWDAF wants to resolve an internal load situation or prepare for a graceful shutdown.

NOTE 3: Handling of overload situation or preparation for a graceful shutdown are preferably executed inside an NWDAF Set, when available.

Figure 6.1B.2.3-1: Prepared analytics transfer

0. Analytics consumer subscribes to the source NWDAF for certain analytics as specified in clause 6.1.1.

0a. Source NWDAF starts data collection from relevant data source(s) (e.g. NFs or OAM) as specified in clause 6.2. Source NWDAF starts generating requested analytics.

0b. [Conditional] (Only if the source NWDAF does not serve the whole PLMN and the requested analytics involves UE related data) The source NWDAF subscribes, using Namf_EventExposure_Subscribe service operation, to receive notifications on UE mobility events from AMF.

1. The source NWDAF determines that it needs to prepare to transfer analytics to another NWDAF instance.

2. The source NWDAF discovers candidate target NWDAF instances (e.g. NWDAFy and NWDAFz) supporting the requested analytics information for the predicted target area(s). NWDAF discovery and selection is specified in clause 6.3.13 of TS 23.501 [2]. In the case of aggregated analytics from multiple NWDAFs, the source NWDAF may use the set of NWDAF identifiers related to aggregated analytics (see clause 6.1.3) to preferably select a target NWDAF that is already serving the consumer.

NOTE 4: In this procedure, NWDAFy and NWDAFz are examples for target NWDAF instances that are candidates to take over those analytic subscriptions.

3-4. In the case of a prepared analytics subscription transfer, the source NWDAF requests, using Nnwdaf_AnalyticsSubscription_Transfer Request, to the candidate target NWDAFs (e.g. NWDAFy and NWDAFz) to prepare for an analytics subscription transfer by including a "prepared analytics subscription transfer indication" in the request message. The request message includes information on the analytics subscriptions to be transferred. The request message may also include "analytics context identifier(s)" indicating the availability of analytics context for particular Analytics ID(s).

The candidate target NWDAFs (e.g. NWDAFy and NWDAFz) respond to the request from the source NWDAF using a Nnwdaf_AnalyticsSubscription_Transfer Response message.

5-6. [Conditional] If "analytics context identifier(s)" had been included in the Nnwdaf_AnalyticsSubscription_Transfer Request received in step 4, the determined target NWDAFs (e.g. NWDAFy and NWDAFz) may request the "analytics context" from the source NWDAF by invoking the "Nnwdaf_AnalyticsInfo_ContextTransferservice" operation. The analytics context transfer procedure is specified in clause 6.1B.3.

NOTE 5: The target NWDAFs (e.g. NWDAFy and NWDAFz) can allocate a new Subscription Correlation ID to the received analytics subscriptions.

7. [Optional] Based on the information received from the source NWDAF, the target NWDAFs (e.g. NWDAFy and NWDAFz) start data collection from NFs or OAM (as specified in clause 6.2) and analytics generation for the indicated analytics subscriptions.

NOTE 6: After step 7, the source NWDAF initiates the analytics subscription transfer to the target NWDAF as specified in steps 4 to 12 of the analytics subscription transfer procedure illustrated in Figure 6.1B.2.2-1.

8. The source NWDAF cancels the prepared analytics subscription transfer to a candidate target NWDAF (e.g. NWDAFz), using Nnwdaf_AnalyticsSubscription_Transfer Request include an "analytics subscription transfer cancel indication". The target NWDAF (e.g. NWDAFz) confirms the cancelation to the source NWDAF and, if applicable, deletes any analytics data that is no longer needed. If the target NWDAF (e.g. NWDAFz), as part of the analytics subscription preparation, had already subscribed to entities to collect data or acquire ML model, it unsubscribes to those entities if the subscriptions are not needed for other active analytics subscriptions with the target NWDAF.

Step 8 may take place any time after step 4 if the NWDAF determines that the candidate target NWDAF (e.g. NWDAFz) does no longer need to prepare for the analytics subscription transfer. In particular, the source NWDAF shall cancel the prepared analytics subscription transfer to all remaining candidate target NWDAFs after one target NWDAF has accepted the analytics subscription transfer (see NOTE 6).

6.1B.3 Analytics Context Transfer

The procedure depicted in Figure 6.1B.3-1 is used by an NWDAF instance to request analytics context from another NWDAF instance, using the Nnwdaf_AnalyticsInfo_ContextTransfer service operation as defined in clause 7.3.3. This procedure, for example, can be invoked in the procedures described in clause 6.1B.2 to request the transfer of relevant analytics context.

Figure 6.1B.3-1: Analytics Context Transfer

The procedure of analytics context information transfer comprises the following steps:

1. The consumer NWDAF requests analytics context by invoking Nnwdaf_AnalyticsInfo_ContextTransfer request service operation. The parameters that can be provided in the request are listed in clause 6.1B.4.

2. The provider NWDAF responds with analytics context to the consumer NWDAF. The analytics context that can be provided in the response is listed in clause 6.1B.4.

If the provider NWDAF stores analytics context (i.e. Historical output Analytics and/or Data related to Analytics) in ADRF, the provider NWDAF may include in the response the ADRF ID together with an indication of the Analytics Context Type stored in the ADRF (i.e. Historical output Analytics and/or Data related to Analytics).

Upon receiving the analytics context, the consumer NWDAF may:

– provide the pending output analytics or historical analytics information to the analytics consumer per the subscription/request;

– use the historical data and analytics metadata in the analytics context to generate analytics;

– subscribe to data collected for analytics with the data sources indicated in the analytics context;

– if the ID(s) of the NWDAF(s) containing MTLF indicated in the analytics context is part of the locally configured (set of) IDs of NWDAFs containing MTLF, retrieve trained ML model(s) from the indicated NWDAF(s) containing MTLF or based on the file address(es) of the trained ML model(s) and use for analytics; and/or

– subscribe to output analytics from the indicated NWDAFs that collectively serve the transferred analytics subscription and perform analytics aggregation on the output analytics using the analytics metadata information, based on the analytics subscription aggregation information.

6.1B.4 Contents of Analytics Context

The Nnwdaf_AnalyticsInfo_ContextTransfer service operation is used to transfer analytics context from a source NWDAF instance to a target NWDAF instance, whereby the target NWDAF consumes the Nnwdaf_AnalyticsInfo_ContextTransfer service operation produced by the source NWDAF instance to request the analytics context as depicted in Figure 6.1B.3-1.

The consumers of the Nnwdaf_AnalyticsInfo_ContextTransfer service operation (as specified in clause 7.3.3) provide the following input parameters:

– A list of analytics context identifier(s): identify a set of analytics context that are available at the NWDAF instance providing this service and that are requested to be transferred to the consumer NWDAF instance. The analytics context identifier is provided as the following:

– Subscription Correlation ID: identifies the analytics subscription for which the related analytics context is requested; or

– A set of SUPI and associated Analytics ID for UE related Analytics; or

– An Analytics ID for NF related Analytics.

– [OPTIONAL] Requested Analytics Context Type per analytics context identifier: indicates which part of the analytics context the consumer wishes to receive. Following values are specified:

– Pending output Analytics;

– Historical output Analytics;

– Analytics subscription aggregation information;

– Data related to Analytics;

– Aggregation related information;

– ML Model related information.

NOTE: A list of "analytics context identifier(s)" can be provided by the source NWDAF to the target NWDAF in an analytics subscriptions transfer request as described in clause 6.1B.2.2. Information allowing to identify an analytics context can also be provided by the NWDAF consumer to the target NWDAF in the Nnwdaf_AnalyticsSubscription_Subscribe request and based on this information the target NWDAF derives the "analytics context identifier", as defined in clause 6.1B.2.1.

The producer NWDAF provides to the consumer of the Nnwdaf_AnalyticsInfo_ContextTransfer service operation (as specified in clause 7.3.3), the output information listed below:

– (Set of) Analytics context matching the input parameters of the Nnwdaf_AnalyticsInfo_ContextTransfer request. If no Requested Analytics Context type parameters are available in the request, all available analytics context types are sent. Analytics context includes the following information parts, if available:

– Analytics related:

– Pending output analytics (i.e. not yet notified to the consumer).

– Historical output analytics information. The content of the output analytics is specified in clause 6.1.3 as output information of the Nnwdaf_AnalyticsSubscription_Notify or Nnwdaf_AnalyticsInfo_Request service operations.

– Timestamp(s) of the last output analytics provided to the analytics consumer(s). Value is set to 0 if no output analytics had been sent yet.

– Analytics subscription aggregation information (only provided when analytics context is related to analytics aggregation): information about the analytics subscriptions that the source NWDAF has with the NWDAFs that collectively serve the transferred analytics subscription, which includes IDs and analytics metadata information of these NWDAFs for specific Analytics ID(s) and optionally input parameters of analytics exposure as defined in clause 6.1.3.

– Data related to Analytics:

– Historical data that is available at the source NWDAF and that is related to the analytics to be handed over to the target NWDAF. If available, the time period of the collected data, NF ID(s) of the data source(s) and information (e.g. filter and event reporting parameters) on the subscriptions with those data sources which were used to generate this historical data.

– Aggregation related information: Related to analytic consumers that aggregate analytics from multiple NWDAF subscriptions:

– (Set of) NWDAF identifiers of NWDAF instances used by the NWDAF service consumer when aggregating multiple analytic subscriptions.

– ML Model related information:

– ID(s) of NWDAF(s) containing MTLF: Instance/Set ID(s) of the NWDAF(s) containing MTLF from which the source NWDAF currently subscribes to the ML Model Information used for the analytics.

– Optionally, file address(es) of the trained ML model(s), which is included only when the source NWDAF itself provides the trained ML model(s) for the analytics subscription(s) for which the related analytics context is requested.