Section: 5.20 External Exposure of Network Capability
Content: 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[ Architecture enhancements for 5G System (5GS) to support network data analytics services ]  [86]). 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[ Procedures for the 5G System (5GS) ]  [3]. 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[ Procedures for the 5G System (5GS) ]  [3] or Network Control parameter in clause 4.15.6.3a of TS 23.502[ Procedures for the 5G System (5GS) ]  [3] 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[ Procedures for the 5G System (5GS) ]  [3] 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[ Procedures for the 5G System (5GS) ]  [3] 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[ Procedures for the 5G System (5GS) ]  [3]. The affected NFs are informed via the subscriber data update as specified in clause 4.15.6.2 of TS 23.502[ Procedures for the 5G System (5GS) ]  [3]. The externally provisioned information which is defined as the Service Parameters in clause 4.15.6.7 of TS 23.502[ Procedures for the 5G System (5GS) ]  [3] 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[ Architecture enhancements for 5G System (5GS) to support network data analytics services ]  [86]. 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[ Procedures for the 5G System (5GS) ]  [3], 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 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. NOTE 1: This is to protect user privacy. NOTE 2: The AF specific UE identifier is ensured to be unique across different AFs as defined in TS 23.003[ Numbering, addressing and identification ]  [19] by configuration. Such configuration is assumed to be coordinated between the different involved entities (e.g. NEF(s) and UDM/UDR). NOTE 3: Based on policies, the NEF can be configured to enforce restriction on the usage of AF specific UE identifier (e.g. rejection of a service request from AF not authorized to use the UE identifier).