Content for  TS 23.288  Word version:  18.4.0

The Data Collection from NFs is based on the services of AMF, SMF, UDM, PCF, NRF, NSACF and AF (possibly via NEF): The Data Collection from NFs is based on the services of AMF, SMF, UDM, PCF, NRF, NSACF, UPF and AF (possibly via NEF):

• Event Exposure Service offered by each NF as defined in clause 4.15 and clause 5.2 of TS 23.502.
• other NF services (e.g. Nnrf_NFDiscovery and Nnrf_NFManagement in NRF as defined in clause 4.17 of TS 23.502)

This data collection service is used directly in order to retrieve behaviour data for individual UEs or groups of UEs (e.g. UE reachability) and also to retrieve global UE information (e.g. Number of UEs present in a geographical area).

To retrieve data related to a specific UE, there are two cases:

• If no Area of interest is indicated by the consumer, the NWDAF shall first determine which NF instances are serving this UE as stated in Table 6.2.2.1-2 unless the NWDAF has already obtained this information due to recent operations related to this UE.
• If an Area of interest is indicated, the NWDAF can:
  • First determine the AMF serving the UE and subscribe UE location from the AMF. Once the UE is in or moves into the Area of interest, the NWDAF determines which NF instances are serving this UE as stated in Table 6.2.2.1-2 unless the NWDAF has already obtained this information due to recent operations related to this UE; or
  • Determine the NF instances of a given type of network function serving the Area of interest by querying NRF unless the NWDAF has already obtained this information due to recent operations related to this UE.

The UDM instance should be determined using NRF as described in clause 4.17.4 of TS 23.502 and factors to determine as described in clause 6.3.8 of TS 23.501. The AMF, SMF instances should be determined using a request to UDM providing the SUPI. To determine the SMF serving a PDU session, the NWDAF should in addition provide the DNN and S-NSSAI of this PDU Session; otherwise the NWDAF will obtain a list of possibly multiple SMFs (e.g. one per PDU session). The BSF instance should be discovered using NRF thanks to optional request parameters (e.g. DNN list, IP domain list, IPv4 address range, IPv6 prefix range) as stated in clause 4.17.4 of TS 23.502 or based on local configuration at the NWDAF. The PCF instance serving UE PDU Session(s) should be determined using a request to BSF with the allocated UE address, DNN and S-NSSAI. To collect data (e.g. current number of UEs registered in a network slice or current number of PDU Sessions established in a network slice) from NSACF, the NSACF instance should be discovered using NRF as specified in clause 6.3.22 of TS 23.501 or based on local configuration at the NWDAF. When NWDAF receives a request addressed to an Internal Group ID from a consumer, NWDAF may need to initiate data collection from several 5GC NFs, such as AMF, SMF, UDM, PCF, AF (e.g. via NEF), etc. If an Area of interest is indicated by the consumer, NWDAF may first discover the instances of the required 5GC NFs deployed in the network, e.g. by querying NRF, otherwise:

• For discovering the UDM, NWDAF can query the NRF with the Internal Group ID as the target of the query.
• For discovering AMF, SMF, PCF, NEF and AF, NWDAF may need to discover all instances in the network by using the Nnrf_NFDiscovery service.

Then, if data needs to be collected from AMF, SMF, UDM and PCF, NWDAF may initiate the data collection with the Internal Group ID as the target, e.g. subscribing to the event exposure in all the instances of a given type of network function. This subscription to all the instances of required source of event exposure handles, e.g. mobility of UEs across AMFs, or initiation of new PDU sessions with different allocated SMFs. For collecting data from AMF and SMF, NWDAF may collect the data directly from AMF and/or SMF, or indirectly via UDM, according to clause 4.15.4.4 of TS 23.502. The indirect method may be required if the event exposure subscription from NWDAF, for a UE or group of UEs, needs to survive the removal of UE context in the AMF including event exposure subscriptions, or upon the creation of new UE context in AMF or SMF serving the UE or group of UEs. In this case the UDM is responsible for (re)creating event exposure subscriptions in AMF and SMF, as specified in clause 4.15.4.4 of TS 23.502. The NWDAF determines to collect data from a trusted AF supporting specific Event ID(s) and serving specific application(s) based on internal configuration. The NEF instance that is serving a specific network slices and/or applications of a UE should be determined using NRF using optional request parameters as defined in clause 6.3.14 of TS 23.501 If NWDAF needs to collect data from an AF deployed outside the operator's domain, the NWDAF shall contact NEF with a SUPI or Internal Group ID as the target of the data collection. NEF is responsible for translation of SUPI to GPSI, or internal to external group identifiers, by querying UDM, prior to contacting the AF. NWDAF may collect data directly from UPF for a specific UE, a group of UEs or for any UEs as defined in clause 5.8.2 of TS 23.501 and in clause 4.15.4.5 of TS 23.502. NWDAF may subscribe indirectly via SMF or directly to UPF for UPF data collection. The direct subscription to UPF event exposure service is only for data collection for any UE e.g., to collect user data usage information for NWDAF NF Load analytic, and if the subscription is not including any of the parameters described in Table 4.15.4.5.1-1 of TS 23.502. To retrieve required data for any UE, the NWDAF may subscribe to events from the AMF and/or SMF instances or UPF instances it has determined, setting the target of event reporting to "any UE" and the event filter(s) according to the Analytics Filter Information. Alternatively, if the required data is communication related and for any UE within an Area of interest, the NWDAF can obtain from the AMF instances it has determined a list of UEs located within the Area of Interest. Based on the obtained UE list, for each UE in the list, the NWDAF retrieves the SMF serving the UE and the NWDAF subscribes to data from the relevant SMF per each specific UE. The indirect event exposure subscription to AMF or SMF via UDM is not available for "any UE" or "any UE within an Area of interest". If the required data is collected from UE via AF as described in clause 6.2.8 and the Target of Analytics Reporting received from consumer is "any UE", the NWDAF may either set the target of event reporting to "any UE" in the data collection request to the AF, or may determine a list of UEs from AMF and/or SMF based on the Analytics Filter Information and send the data collection request to the AF for the determined list of UEs. To retrieve data related to "any UE" based on Analytics Filter Information, the NWDAF shall first determine which NF instances are matching the Analytics Filter Information (see clause 6.7.5.1) as stated in Table 6.2.2.1-3 unless the NWDAF has already obtained this information due to recent operations related to this Analytics Filter Information.

To retrieve data related to Analytics IDs for "any UE" with Analytics Filter Information defining an area of interest in terms of TA or Cells and/or with specific S-NSSAIs, NWDAF requires the network slice association information to properly determine the AMFs to collect data from as well as the proper queries to OAM for data collection. The network slice association information comprises the TAs associated with each AMF and for each TAI its associated access type, cells and list of supported S-NSSAIs (including indication of S-NSSAIs restricted by AMF). Additionally, the mapping of cells per TAI and supported S-NSSAIs (including indication of S-NSSAIs restricted by AMF) for TAI for each AMF can change and NWDAF shall obtain this accurate information in order to properly retrieve data for analytics generation. In order to derive the network slice association information, NWDAF may be configured with the mapping of cells per TAI and the S-NSSAIs per TAI. NWDAF may subscribe to the "S-NSSAIs per TAI mapping" event exposed by AMF. The NWDAF may use the configured information (when the analytics subscription or request is at cell granularity) and the area of interest in the analytics subscription or request to retrieve from AMF the list of supported S-NSSAIs (including indication of S-NSSAIs restricted by AMF) per TAI and access types per TAI for each AMF in the required area of interest. NWDAF consumes the "S-NSSAI per TAI mapping" event exposed by AMF using, as target of event reporting, the list of TAIs based on the area of interest received in the Analytics Filter Information or identified by the mapping of the Cells per TAI matching to the Cell granularity included in the Analytics Filter Information. The AMF "S-NSSAIs per TAI mapping" event output contains, for each of the TAIs requested by NWDAF, its associated access type and the list of supported S-NSSAIs (including indication of S-NSSAIs restricted by AMF). To retrieve data from SMFs for Analytics IDs subscription or requests for "any UE" including Analytics Filter Information with specific Applications, DNNs, DNAIs and area of interest per TA granularity, NWDAF shall first discover the SMF serving the area of interest via NRF. NWDAF may directly consume events from the discovered SMF using the event target set to "any PDU session" and event filters with the same parameters of the Analytics Filter Information, i.e. list of Application IDs and/or DNNs and/or DNAI and the area of interest related to the requested Analytics ID.

1. When SMF supports the exchange of UE Location parameter when SMF interacts with AMF via Nsmf_PDUSession_Create/Update/CreateSMContext/UpdateSMContext due to session establishment, modification, or release, service request, or handover procedures (as defined in clause 5.2.8.2 of TS 23.502), SMF can directly map the PDU sessions to an AoI with TA granularity.
   If there are any changes in PDU sessions in the area of interest, for the Application ID and/or DNN and/or DNAI subscribed by NWDAF, SMF notifies the detected changes to NWDAF via Nsmf_EventExposure_Notify service operation, enabling NWDAF to keep an updated map of SMF and PDU sessions associated with the Analytics Filter Information in an area of interest.
2. When SMF does not support the exchange of UE Location parameter when SMF interacts with AMF but supports the mapping of PDU sessions per TA (as defined in clause 5.6.11 of TS 23.501), SMF may subscribe to UE mobility event notifications of AMF as described in clause 5.3.4.4 of TS 23.501 using event ID "UE moving in or out of Area of Interest" and Event Filters as described in Table 5.2.2.3.1-1 from TS 23.502 to retrieve the list of SUPIs (and GPSIs if available) in the area of interest. Based on the retrieved list of SUPIs in the area of interest, SMF identifies the PDU sessions in the area of interest.
3. When SMF does not support the exchange of UE Location parameter when SMF interacts with AMF nor supports the mapping of PDU sessions per TA (as defined in clause 5.6.11 of TS 23.501), SMF rejects the request from NWDAF. Upon the reject, NWDAF identifies the need to create the mapping of PDU sessions per TA. NWDAF subscribes to UE mobility event notifications of AMF as described in clause 5.3.4.4 of TS 23.501 using event ID "UE moving in or out of Area of Interest" and Event Filters as described in Table 5.2.2.3.1-1 from TS 23.502 to retrieve the list of SUPIs (and GPSIs if available) in the area of interest. Based on the retrieved list of SUPIs in the area of interest, NWDAF subscribes to the SMFs serving the UEs in the area of interest and derives the mapping of PDU sessions per TA.

An NWDAF may require to discover and select other NWDAFs for UE related analytics. In this case, the NWDAF may discover from UDM if an NWDAF is already collecting data related to the UE, as specified in clauses 5.2 and 6.1C.

The procedure in Figure 6.2.2.2-1 is used by NWDAF to subscribe/unsubscribe at NFs in order to be notified for data collection on a related event (s), using Event Exposure Services as listed in Table 6.2.2.1-1. Depending on local regulation requirements, user consent for UE related data collection and usage of collected data may be required. User consent is defined for a specific purpose such as, e.g. analytics or model training. NWDAF checks user consent taking the purpose for data collection and usage of these data into account.

The procedure in Figure 6.2.2.3-1 is used by NWDAF to collect information from AFs via the NEF. The AF collectable data information includes: AF identification, AF service identification (e.g. endpoint information of Naf_EventExposure), available data to be collected per application (e.g. identified by Event ID(s)).

The NWDAF may use NRF services and Network Function service framework procedures as defined in clause 5.2.7 and clause 4.17 of TS 23.502:

• NF/NF service discovery procedures (in clause 4.17.4 of TS 23.502) and Nnrf_NFDiscovery service (in clause 5.2.7.3 of TS 23.502) in order to dynamically discover the NF instances and services of the 5GC. Such discovery may be performed on a periodic basis, or under specific circumstances.
• NF/NF service status subscribe/notify procedures (in clause 4.17.7 of TS 23.502) and Nnrf_NFManagement service (in clause 5.2.7.2 of TS 23.502) in order to be notified about the change of status of an NF. The service operations for obtaining status information are NFStatusSubscribe and NFStatusNotify, from the Nnrf_NFManagement service.

The information provided by the NRF to the NWDAF with the Nnrf_NFDiscovery_Request and the Nnrf_NFManagement_NFStatusNotify service operations are the NF Profiles and the NF services as defined in clause 5.2.7 of TS 23.502. Such information can be used to set-up and maintain a consistent network map for data collection and also, depending on use cases, to perform analytics (e.g. NF load analytics as defined in clause 6.5). If the NWDAF needs to keep a consistent network map for data collection from AMFs and SMFs associated with a list of TAs, the subscription to NFStatusSubscribe for such type of NFs may include the list of TAs target.

The NWDAF shall subscribe (and unsubscribe) to the Event exposure service from NF(s) reusing the framework defined in clause 4.15 of TS 23.502. This framework supports the possibility for the NWDAF to indicate/request:

• Events-ID: one or multiple Event ID(s) defined in clause 4.15.1 of TS 23.502.
• Target of Event Reporting defined in clause 4.15.1 of TS 23.502: the objects targeted by the Events. Within a subscription, all Event ID(s) are associated with the same target of event reporting. In the case of NWDAF, the objects can be UE(s), UE group(s), any UE.
• Event Filter Information defined in clause 4.15.1 of TS 23.502. This provides Event Parameter Types and Event Parameter Value(s) to be matched against.
• A Notification Target Address and a Notification Correlation ID as defined in clause 4.15.1 of TS 23.502, allowing the NWDAF to correlate notifications received from the NF with this subscription.
• Event Reporting Information described in TS 23.502 Table 4.15.1-1 and the muted stored events exposure as described in clause 6.2.7.
• Expiry time as defined in clause 4.15.1 of TS 23.502.

The notifications from NFs/AFs contain on top of the Event being reported (and of dedicated information being reported for this event):

• the Notification Correlation Information provided by the NWDAF in its request;
• (when applicable to the event) the Target Id e.g. UE ID (SUPI and if available GPSI); and
• a time stamp.