Content for  TS 23.501  Word version:  18.5.0

The Network Exposure Function (NEF) supports external exposure of capabilities of network functions. External exposure can be categorized as Monitoring capability, Provisioning capability, Policy/Charging capability, Analytics reporting capability and Member UE selection capability. The Monitoring capability is for monitoring of specific event for UE in 5G System and making such monitoring events information available for external exposure via the NEF. The Provisioning capability is for allowing external party to provision of information which can be used for the UE in 5G System. The Policy/Charging capability is for handling access and mobility management, QoS and charging policies for the UE based on the request from external party. The Analytics reporting capability is for allowing an external party to fetch or subscribe/unsubscribe to analytics information generated by 5G System (this is further defined in TS 23.288). The Member UE selection capability is for allowing an external party to acquire one or more list(s) of candidate UE(s) (among the list of target member UE(s) provided by the AF) and additional information that is based on the assistance information generated by 5G System based on some defined filtering criteria, the details are explained in clause 4.15.13 in TS 23.502. Monitoring capability is comprised of means that allow the identification of the 5G network function suitable for configuring the specific monitoring events, detect the monitoring event, and report the monitoring event to the authorised external party. Monitoring capability can be used for exposing UE's mobility management context such as UE location, reachability, roaming status, and loss of connectivity. Monitoring capability can also be used for exposing QoS monitoring result. AMF stores URRP-AMF information in the MM context to determine the NFs that are authorised to receive direct notifications from the AMF. UDM stores URRP-AMF information locally to determine authorised monitoring requests when forwarding indirect notifications. The Monitoring capability also allows AF to subscribe to the group status changes for a group, either a 5G VN group as described in clause 5.29.2, as well as a group configured by OA&M. In this case the AF is notified if the group member list is updated or a group member is no longer subscribed to the group. Provisioning capability allows an external party to provision the Expected UE Behaviour or the 5G-VN group information or DNN and S-NSSAI specific Group Parameters or ECS Address Configuration Information or service specific information to 5G NF via the NEF. The provisioning comprises of the authorisation of the provisioning external third party, receiving the provisioned external information via the NEF, storing the information, and distributing that information among those NFs that use it. The externally provisioned data can be consumed by different NFs, depending on the data. In the case of provisioning the Expected UE Behaviour, the externally provisioned information which is defined as the Expected UE Behaviour parameters in clause 4.15.6.3 of TS 23.502 or Network Control parameter in clause 4.15.6.3a of TS 23.502 consists of information on expected UE movement, Expected UE Behaviour parameters or expected Network Configuration parameter. The provisioned Expected UE Behaviour parameters may be used for the setting of mobility management or session management parameters of the UE. In the case of provisioning the 5G-VN group information the externally provisioned information is defined as the 5G-VN group parameters in clause 4.15.6.7 of TS 23.502 and it consists of some information on the 5G-VN group. In the case of the provisioning the DNN and S-NSSAI specific Group Parameters, the externally provisioned information is defined in clause 4.15.6.14 of TS 23.502, and clause 5.20b. In the case of provisioning ECS address, the externally provisioned information is defined as the ECS Address Configuration Information in clause 4.15.6.3d of TS 23.502. The affected NFs are informed via the subscriber data update as specified in clause 4.15.6.2 of TS 23.502. The externally provisioned information which is defined as the Service Parameters in clause 4.15.6.7 of TS 23.502 consists of service specific information used for supporting the specific service in 5G system. The provisioned Service Parameters may be delivered to the UEs. The affected NFs are informed of the data update. Policy/Charging capability is comprised of means that allow the request for session and charging policy, enforce QoS policy, apply accounting functionality and requests to influence access and mobility management policies. It can be used for specific QoS/priority handling for the session of the UE, and for setting applicable charging party or charging rate. Analytics reporting capability is comprised of means that allow discovery of type of analytics that can be consumed by external party, the request for consumption of analytics information generated by NWDAF. Member UE selection capability is comprised of means that allows filtering and providing one or more list(s) of candidate UE(s) (among the list of target member UE(s) provided by the AF) and additional information that can be consumed by external party, the request for consumption of UE list generated by external party. An NEF may support CAPIF functions for external exposure as specified in clause 6.2.5.1. An NEF may support exposure of NWDAF analytics as specified in TS 23.288. The NEF may support exposure of 5GS and/or UE availability and capabilities for time synchronization service as specified in clause 5.27.1.8. An NEF may support exposure of event based notifications and reports for NSACF as specified in clause 5.15.11. An AF may only be able to identify the target UE of an AF request for external exposure of 5GC capabilities (e.g. Data Provisioning or for Event Exposure for a specific UE) by providing the UE's address information. In this case the NEF first needs to retrieve the Permanent identifier of the UE before trying to fulfil the AF request. The NEF may determine the Permanent identifier of the UE, as described in clause 4.15.3.2.13 of TS 23.502, based on:

• the address of the UE as provided by the AF; this may be an IP address or a MAC address;
• the corresponding DNN and/or S-NSSAI information: this may have been provided by the AF or determined by the NEF based on the requesting AF; this is needed if the UE address is an IP address.

The NEF may provide a UE Identifier in the GPSI format of MSISDN to a trusted AF:

• that fulfils the conditions described in clause 4.15.10A of TS 23.502; and
• that has explicitly requested a translation from the UE address to a unique UE identifier (via Nnef_UEId service) when the UE MSISDN exposure is allowed and authorized by the operator; or
• the NEF may provide an AF specific UE Identifier to the AF:
  • that has explicitly requested a translation from the address of the UE to a unique UE identifier (via Nnef_UEId service); or
  • that has implicitly requested a translation from the address of the UE to a AF specific UE Identifier by requesting external exposure about an individual UE identified by its address.

The AF may have its own means to maintain the AF specific UE Identifier through, e.g. an AF session. After the retrieval of an AF specific UE Identifier the AF shall not keep maintaining a mapping between this identifier and the UE IP address as this mapping may change. The AF specific UE Identifier shall not correspond to a MSISDN; it is represented as a GPSI in the form of an External Identifier. When used as an AF specific UE identifier, the External Identifier provided by the 5GCN shall be different for different AF.

An NF that needs to collect data from an AF may subscribe/unsubscribe to notifications regarding data collected from an AF, either directly from the AF or via NEF. The data collected from an AF is used as input for analytics by the NWDAF. The details for the data collected from an AF as well as interactions between NEF, AF and NWDAF are described in TS 23.288.

NEF provisioning capability as defined in clause 5.20 allows an AF to perform provisioning of traffic characteristics and monitoring of performance characteristics for a group of UEs as specified in clause 4.15.6.14 of TS 23.502 and clause 6.1.3.28 of TS 23.503. The NEF determines whether or not to invoke the TSCTSF in the same way as for AF session with required QoS procedure, as described in step 2 of clause 4.15.6.6 of TS 23.502. In the case that the TSCTSF is used, the TSCTSF receives the AF requested QoS information from the NEF. In the case that TSCTSF is not used, the AF request is handled as described in clause 4.15.6.14 of TS 23.502 and clause 6.1.3.28 of TS 23.503. When the TSCTSF receives the AF requested QoS information from NEF or the PCF(s) receive the AF requested QoS information from UDR, the TSCTSF or PCF (s) manage the AF requested QoS information for each UE group member within the group as follows:

• Translate the External Group ID into a list of SUPIs by invoking Nudm_SDM_Get service.
• Determine which of these UE group members have active PDU Sessions matching the DNN and S-NSSAI and determine the relevant UE address.
• Manage the request status (activated, de-activated, failed) for each UE group member within the group:
  • Apply the AF requested QoS information if the UE group member is registered or has active PDU Session matching the DNN and S-NSSAI. Set the status to activated if the QoS resources are assigned for the UE group member, otherwise, failed.
  • Set the status to de-activated if the UE group member is not registered or has no active PDU Session matching the DNN and S-NSSAI.
  • Delete the request status for the UE group member if the UE group member is removed from the group, and further revokes AF request QoS information if the request status is activated.
  • Check whether to apply the AF requested QoS information and update the request status for the UE group member if the UE group member is newly added to the group.
• When the AF requested QoS information contains temporal invalidity condition as described in clause 6.1.3.28 of TS 23.503:
  • Revoke AF requested QoS information for each UE group member which is marked as active, so to e.g. to remove or modify PCC rules as defined in clause 4.16.5.2 of TS 23.502 if the start-time is reached.
  • Apply AF requested QoS information for each UE group member that has active PDU Sessions matching the DNN and S-NSSAI, e.g. to add or modify PCC rules as defined in clause 4.16.5.2 of TS 23.502 if the end-time is reached.