Section: 5.2.8.3 Nsmf_EventExposure Service 5.2.8.3.1 General
Content: Service description: This service provides events related to PDU Sessions towards consumer NF. The service operations exposed by this service allow other NFs to subscribe and get notified of events happening on PDU Sessions. The following are the key functionalities of this NF service. - Allow consumer NFs to Subscribe and unsubscribe for an Event ID on PDU Session(s); - Allow the NWDAF to collect data for network data analytics from SMF as specified in TS 23.288[ Architecture enhancements for 5G System (5GS) to support network data analytics services ]  [50] and from UPF as specified in clause 4.15.4.5; - Notifying events on the PDU Session to the subscribed NFs; and - Allow consumer NFs to acknowledge or respond to an event notification. The following events can be subscribed by a NF consumer (Event ID is defined in clause 4.15.1): - UE IP address / Prefix allocation/change: The event notification may contain a new UE IP address / Prefix or an indication of which UE IP address / Prefix has been released. - PDU Session Establishment and/or PDU Session Release. The event notification may contain following information: - PDU Session Type. - DNN. - UE IP address/Prefix. - UP path change: a notification corresponding to this event is sent when the UE IP address / Prefix and / or DNAI and /or the N6 traffic routing information has changed. The event notification may contain following information: - the type of notification ("EARLY" or "LATE"). - for both the source and target UP path between the UE and the DN, the corresponding information is provided when it has changed: - DNAI. - UE IP address / Prefix. - N6 traffic routing information. - Candidate DNAI(s) for the PDU Session. - Change of common EAS. NOTE 1: UP path change notification, DNAI and N6 traffic routing information are further described in clause 5.6.7 of TS 23.501[ System architecture for the 5G System (5GS) ]  [2]. - QoS Monitoring: the event notification may contain the QoS Monitoring report for the QoS parameter(s) to be measured defined in clause 5.45 of TS 23.501[ System architecture for the 5G System (5GS) ]  [2]. Implicit subscription of the PCF on behalf of the NEF/AF as part of setting PCC rule(s) may trigger SMF to send this event notification. - Change of Access Type; The event notification contains the new Access Type for the PDU Session. For MA PDU Session the Change of Access Type may include two Access Type information that the user is currently using. - Change of RAT Type; the event notification contains the new RAT Type for the PDU Session. - PLMN change; The event notification contains the new PLMN Identifier for the PDU Session. - Change of satellite backhaul category; The event notification contains the new satellite backhaul category for the PDU session. - Downlink data delivery status. The event notification contains the status of downlink data buffering in the core network including: - First downlink packet per source of the downlink IP traffic in extended buffering and Estimated maximum wait time. - First downlink packet per source of the downlink IP traffic discarded. - First downlink packet per source of the downlink IP traffic transmitted after previous buffering and/or discarding of corresponding packet(s). - QFI allocation: The event notification is sent when a new QoS flow is established within a PDU session and contains: - If the Target of Event Reporting is a PDU session, both the allocated QFI and either one of the following (Application Identifier or IP Packet Filter Set or Ethernet Packet Filter Set). The 5QI corresponding to the QoS flow and the DNN, S-NSSAI corresponding to the PDU session are also sent. - If the Target of Event Reporting is a SUPI, both the allocated QFI and either one of the following (Application Identifier or IP Packet Filter Set or Ethernet Packet Filter Set) for each PDU session ID established for this SUPI. The 5QI corresponding to the QoS flow and the DNN, S-NSSAI corresponding to each PDU session are also sent. - If the Target of Event Reporting is an Internal-Group-Id or any UE, multiple instances of the tuple (allocated QFI and either one of the following (Application Identifier or IP Packet Filter Set or Ethernet Packet Filter Set). PDU session ID, SUPI). The 5QI corresponding to the QoS flow and the DNN, S-NSSAI corresponding to each PDU session are also sent. - Total number of Session Management transactions: - The total number of Session Management transaction is used to collect the number of SM transactions of a SUPI or Internal Group ID, for example Dispersion Analytics as specified in TS 23.288[ Architecture enhancements for 5G System (5GS) to support network data analytics services ]  [50]. The transaction count is incremented when the NAS transactions from PDU Session Establishment, PDU Session Authentication, PDU Session Modification and PDU Session Release procedures is concluded. Only the periodic reporting mode applies. - Information on PDU Session for WLAN (i.e. Access Type is Non-3GPP and RAT Type is TRUSTED_WLAN). NOTE 2: When the consumer NF is the NWDAF, the event QFI allocation is used to collect data for Observed Service Experience analytics, UE communication analytics, QoS Sustainability analytics and end-to-end data volume transfer time analytics as specified in TS 23.288[ Architecture enhancements for 5G System (5GS) to support network data analytics services ]  [50]. - User plane status information: The event notification contains: - PDU Session ID. - User Plane Inactivity Timer (as specified in TS 29.244[ Interface between the Control Plane and the User Plane nodes ]  [69]). - PDU Session status (activated, deactivated). NOTE 3: When the consumer NF is the NWDAF, the event user plane status information is used to collect data for UE Communication analytics as specified in TS 23.288[ Architecture enhancements for 5G System (5GS) to support network data analytics services ]  [50]. - Session Management Congestion Control Experience for PDU Session: The event notification contains the data related to Session Management Congestion Control experience per PDU Session as described in TS 23.288[ Architecture enhancements for 5G System (5GS) to support network data analytics services ]  [50]. - UE session behaviour trends (see clause 4.15.4.3); - UE communications trends (see clause 4.15.4.3); - UP with redundant transmission: the event notification indicates if redundant transmission (see clause 5.33.2.2 of TS 23.501[ System architecture for the 5G System (5GS) ]  [2]) has been activated or not for the PDU session; - User Data Usage Measures (see clause 4.15.4.5): SMF conveys the subscription to UPF on behalf of the consumer. Consumer receives the events directly from UPF; and - User Data Usage Trends (see clause 4.15.4.5): SMF conveys the subscription to UPF on behalf of the consumer. Consumer receives the events directly from UPF. When the consumer NF is the NWDAF, the event Information on PDU Session for WLAN is used to collect data for WLAN performance analytics as specified in TS 23.288[ Architecture enhancements for 5G System (5GS) to support network data analytics services ]  [50]. When the consumer NF is the NWDAF, the event Session Management Congestion Control Experience for PDU Session is used to collect data for Session Management Congestion Control Experience analytics as specified in TS 23.288[ Architecture enhancements for 5G System (5GS) to support network data analytics services ]  [50]. When the consumer NF is the NWDAF, the events QoS Monitoring, User Data Usage Measures and User Data Usage Trends are used to collect data from UPF for analytics as specified in clause 4.15.4.5 and in TS 23.288[ Architecture enhancements for 5G System (5GS) to support network data analytics services ]  [50]. SMF conveys the subscription to UPF on behalf of the NWDAF. The consumer NF may request to subscribe the UPF exposure events (including event ID of exposed UPF event of QoS monitoring, User Data Usage Measures and User Data Usage Trends) via SMF indirectly by Nsmf_EventExposure. After receiving this subscription request, the SMF does a third-party subscription onto UPF on behalf of this consumer. The consumer should also provide the subscribed UPF event to SMF. Event Filters are used to specify the conditions to match for notifying the events (i.e. "List of Parameter values to match"). If there are no conditions to match for a specific Event ID, then the Event Filter is not provided. The following table provides as an example how the conditions to match for event reporting can be specified for various Event IDs for SMF exposure. Table 5.2.8.3.1-1: Example of Event Filters for SMF exposure events The target of SMF event reporting may correspond to a PDU Session ID, an UE ID (SUPI), an Internal Group Identifier, an indication that any UE is targeted (e.g. on a specific DNN), or an indication that any PDU session is the target. When acknowledgment is expected the SMF also provides Notification Correlation Information to the consumer NF in the event notification. The consumer NF may provide the following event-specific information when acknowledging an event notification: - For UP path change event: - N6 traffic routing information related to the target DNAI. NOTE 4: Acknowledgement to a UP path change event notification is further described in clause 5.6.7 of TS 23.501[ System architecture for the 5G System (5GS) ]  [2].