5.20 External Exposure of Network Capability

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 [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 [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 or Static IP address assignment parameters 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 [3] or Network Control parameter in clause 4.15.6.3a of TS 23.502 [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 [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 [3] and clause 5.20b. In the case of provisioning non-3GPP device Identifier information, the externally provisioned information is defined as the non-3GPP device Identifier information in clause 4.15.6.15 of TS 23.502 [3]. 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 [3]. The affected NFs are informed via the subscriber data update as specified in clause 4.15.6.2 of TS 23.502 [3]. The externally provisioned information which is defined as the Service Parameters in clause 4.15.6.7 of TS 23.502 [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 [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 NEF may support energy related functionality as specified in clause 5.51.

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 [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 a UE Identifier in the GPSI format of MSISDN to an authenticated and authorized AF:

• that fulfils the conditions described in clause 4.15.10A of TS 23.502 [3]; 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 an 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 [19]. The AF specific UE identifier can be configured in the UDR and in such case, the configuration is assumed to be coordinated between the different involved entities (e.g. NEF(s) and UDM/UDR).

Alternatively, based on local configuration, the AF specific UE identifier can be dynamically generated by the UDM, via implementation specific means, when there is no AF specific UE identifier defined in UDR and if the requesting AF is authorized to receive an AF specific UE identifier for this subscriber. In this case, the AF specific UE identifier is generated by the UDM so that it is possible for the UDMs to translate the generated AF specific UE identifier to its corresponding SUPI.

The dynamically generated AF specific UE identifier can optionally be stored by the UDM in the UDR if furthermore required by local policies; in that case the generated AF specific UE identifier stored in UDR can be used during the execution of subsequent Nnef_UEId services. Additionally, the operator can trigger the renewal of the AF Specific UE identifier by e.g. replacing or removing the AF Specific UE identifier stored in UDR. At the execution of a subsequent Nnef_UEId service, the UDM provides a new AF specific UE identifier for the UE e.g. as replaced in UDR or as generated by UDM if no AF specific UE identifier is present in UDR. The UDM rejects any AF/NEF service request using AF Specific UE identifiers that does not match an AF specific UE identifier present in 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).

The NEF may also provide MSISDN verification (via Nnef_UEId service) to an authenticated and authorized AF that fulfils the conditions described in clause 4.15.10B of TS 23.502 [3].