Content for  TS 23.502  Word version:  18.5.0

The network capability exposure comprises

• Exposure of network events externally as well as internally towards core network NFs;
• Exposure of provisioning capability towards external functions;
• Exposure of policy and charging capabilities towards external functions;
• Exposure of core network internal capabilities for analytics.
• Exposure of analytics to external party.
• Retrieval of data from external party by NWDAF.
• Exposure of number of registered UEs and/or established PDU Sessions for a network slice that is subject to Network Slice Admission Control towards core network NFs or external party.
• Exposure of Member UE selection assistance information including list(s) of candidate UEs based on the UE list provided by the AF and possibly additional information that fulfil some Member UE filtering criteria provided by the AF.

When subscribing to event reporting the NF consumer(s) provide:

• One or multiple Event ID(s). An Event ID identifies the type of event being subscribed to (e.g. PDU Session Release, UE mobility out of an Area of Interest, etc.).
• Event Filter Information: Provides Event Parameter Types and Event Parameter Value(s) to be matched against, in order to meet the condition for notifying the subscribed Event ID e.g. the Event Parameter Type could be "Area of interest" and Event Parameter Value list could be list of TAs; The Event Filter depends on the Event ID. The Event Filter Information is provided per Event ID(s) being subscribed to: within a subscription different Event ID(s) may be associated with different Event Filter Information.
• Event Reporting Information described in the Table 4.15.1-1 below. Within a subscription all Event ID(s) are associated with a unique Event Reporting Information.
• Target of Event Reporting: this may indicate a specific UE or PDU Session, a group of UE(s) or any UE (i.e. all UEs), Within a subscription all Event ID (s) are associated with the same Target of Event Reporting (possibly corresponding to multiple UE or multiple PDU Sessions).
• A Notification Target Address (+ Notification Correlation ID) allowing the Event Receiving NF to correlate notifications received from the Event provider with this subscription. A subscription is associated with an unique Notification Target Address (+ Notification Correlation ID). In the case that the NF consumer subscribes to the NF producer on behalf of other NF, the NF consumer includes the Notification Target Address(+Notification Correlation ID) of other NF for the Event ID which is to be notified to other NF directly and the Notification Target Address(+Notification Correlation ID) of itself for the Subscription change related event notification. Each Notification Target Address(+ Notification Correlation ID) is associated with related (set of) Event ID(s).
• An Expiry time represents the time upto which the subscription is desired to be kept as active. The NF service consumer may suggest an Expiry time and provide to the NF service producer. Based on the operator's policy, the NF service producer decides whether the subscription can be expired. If the subscription can be expired, the NF service producer determines the Expiry time and provide it in the response to the NF service consumer. If the event subscription is about to expire based on the received Expiry time and the NF service consumer wants to keep receiving notifications, the NF service consumer update the subscription with the NF service producer in order to extend the Expiry time. Once the Expiry time associated with the subscription is reached, the subscription becomes invalid at the NF service producer. If the NF service consumer wants to keep receiving notifications, it shall create a new subscription with the NF service producer.

When the subscription is accepted by the Event provider NF, the consumer NF receives from the event provider NF an identifier (Subscription Correlation ID) allowing to further manage (modify, delete) this subscription. The consumer NF may use an operation dedicated to subscription modification to add or remove Event ID(s) to this subscription or to modify Event Filter Information. Events are subscribed by the consumer NF(s) by providing Event Filters. The contents of the Event Reporting Information along with the presence requirement of each information element is described in Table 4.15.1-1.

  Maximum number of reports is applicable to the subscription to one UE or a group of UE(s). When the subscription is applied to a group of UE(s), the initial value of the parameter is applied to each individual member UE. The count of number of reports is per UE and per Event Type granularity also for group member UE. Maximum duration of reporting is applicable to the subscription to one UE, a group of UE(s) or any UE. When the subscription is applied to a group of UE(s), this parameter applies to each group member UE. When the subscription is applied to any UE, this parameter applies to all the impacted UEs. If for a given subscription Maximum duration of reporting is included then the subscription is cancelled locally in the NF as soon as Maximum duration of reporting is reached. If the Maximum number of reports is reached for a given subscription, the NEF cancels the subscription in the affected NFs. If both Maximum Number of reports and Maximum duration of reporting are included then the subscription expires or is cancelled as soon as one of the conditions is met. Sampling ratio is applicable to subscription targeting a group of UEs or any UE. When a sampling ratio is provided, a random subset is selected among the target UEs according to the sampling ratio and only the events related to this subset are reported. A UE remains selected until it is no longer managed by the event provider NF. A UE newly managed by the NF may be selected. Partitioning criteria are applicable to subscription targeting a group of UEs or any UE and may be used when sampling ratio is used. These criteria are used to instruct the NF on how to group the UEs before applying the sampling ratio. When partitioning criteria are provided, the NF groups the targeted UEs (i.e. creates sub-populations/strata) based on the partition criteria parameter. Then, from each sub-population/stratum, the NF selects a subset of UEs by sampling randomly from each sub-population according to the sampling ratio. For a given type of partitioning criteria, the UE belongs to a single sub-population/stratum as long as it is served by the NF. The types of Partitioning Criteria are described in Table 4.15.1-2:

  Group Reporting Guard Time is an optional parameter for group-based monitoring configuration to indicate the time for which the Monitoring Event Reporting(s) related with the UEs in a group can be aggregated before sending them to the consumer NF. The value of the Group Reporting Guard time should be set less than the Maximum duration of reporting. For the continuous monitoring reporting, unless the Maximum duration of reporting has been reached, the Group Reporting Guard timer is restarted when it expires. If the time left until the Maximum duration of reporting is less than the Group Reporting Guard Time, then the Group Reporting Guard timer shall be set to expire when the Maximum duration of reporting expires. If the Maximum duration of reporting is expired, the Group Reporting Guard Time, if running, shall be considered to expire and aggregated Monitoring Event Reporting(s) is sent to destination immediately. Deactivation notification flag and retrieval notification flag enable the mute storage of events for a limited size of events at the Event provider NF, thus reducing the number of notifications and the overall signalling between the Event provider NF and the Event consumer NF. Usage of these parameters is further specified in clause 6.2.7 of TS 23.288. Muting Exception Instructions specify actions to be taken by the Event provider NF if the Deactivation notification flag is set and an exception occurs at the Event Producer NF (e.g. the Event provider can no longer buffer notifications because storage space is no longer available). The actions are specified in clause 6.2.7 of TS 23.288. Granularity of dynamics indicates negligible changes in the target event of the subscription for which notification is not required. The changes in the Granularity of dynamics are depicted as the range of scalar value (x, y) where it means [the previously notified scalar value - x, the previously notified scalar value + y), the list of event identification(s) (e.g. list of SUPI(s)), or the previous notification. If the Granularity of dynamics is provided, the provider NF shall send the notification only when the changes in the target event are not described in the Granularity of dynamics, except for the first notification. Reporting type is a parameter to reduce the data volume of notification. If the Reporting type is provided, the provider NF shall notify the events that have been newly appeared, disappeared and changed compared to the previous notification, except for the first notification. Table 4.15.1-1 indicates the presence requirements for the Event Reporting Information. Corresponding notifications contain at least the Notification Correlation ID together with the Event ID and the individual target (e.g. UE or PDU Session ID) associated with the notification. If the NF service consumer decides to terminate the event subscription, it unsubscribes the event subscription by sending unsubscription request to the event provider NF. After receiving unsubscription request from the NF service consumer, the event provider NF terminates the event subscription. If the NF service consumer has subscribed to group-based monitoring, then the NF service consumer may subsequently unsubscribe to the whole group or one or more identified group member UEs. Such partial cancellation of group-based monitoring does not affect the other group member UEs, but it only cancels the monitoring event subscription for the identified group member UEs. Partial cancellation of group-based monitoring can be caused by the following reasons:

• UE's subscription is discontinued in the UDM;
• UE's authorisation to the subscribed event type is revoked;
• The subscribing NF explicitly unsubscribes to monitoring of selected UE(s); or
• UE is removed from the monitoring target group that was identified in monitoring subscription.

If the NF service consumer has subscribed to group-based monitoring and later new group member UEs are added to the group, then the NF service consumer may also subsequently add monitoring event subscription for the new group member UEs. The following clauses describe the external exposure of network capabilities and core network internal event and capability exposure. When the immediate reporting flag is set, the first corresponding event report is included in the subscription response message, if corresponding information is available at the reception of the subscription request of the event. During Monitoring Event Subscription as in clause 4.15.3, Parameter Provisioning as in clause 4.15.6, NIDD configuration as in clause 4.25.3 and Enhanced Coverage Restriction Control as in clause 4.27.1, the optional parameter MTC Provider Information is a reference parameter that may be provided by AF or determined by NEF based on which AF it communicates with. The MTC Provider Information identifies the MTC Service Provider and/or MTC Application.

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, network status reporting capability, Analytics reporting capability and Member UE selection assistance capability. The Monitoring capability is for monitoring of specific event for UE in 5GS 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 5GS. The Policy/Charging capability is for handling QoS and charging policy for the UE based on the request from external party. The Analytics capability is for allowing external party to acquire analytics information generated by 5G System. The Member UE selection assistance capability enables the NEF to consolidate information collected from other 5GC NFs, which fulfil the Member UE filtering criteria requested by the AF, to derive one or more lists of UE(s) and possibly additional information that assists AF for the selection of candidate members to participate in the application layer operation e.g. federated learning operation in the application layer. The details for the External Exposure of Analytics capabilities as well as interactions between NEF, external party and NWDAF are described in TS 23.288.

The Network Exposure Function (NEF) supports the capability to collect data from an AF as specified in TS 23.501.