4.15.3 Event Exposure using NEF

23.5023GPPProcedures for the 5G System (5GS)Release 18TS

Tools: ARFCN - Frequency Conversion for 5G NR/LTE/UMTS/GSM

4.15.3.1 Monitoring Events

The Monitoring Events feature is intended for monitoring of specific events in 3GPP system and making such monitoring events information reported via the NEF. It is comprised of means that allow NFs in 5GS for configuring the specific events, the event detection and the event reporting to the requested party.

To support monitoring features in roaming scenarios, a roaming agreement needs to be made between the HPLMN and the VPLMN. If the AMF/SMF in the VPLMN determine that normalisation of an event report is required, the AMF/SMF normalises the event report before sending it to the NEF.

The set of capabilities required for monitoring shall be accessible via NEF to NFs in 5GS. Monitoring Events via the UDM, the AMF, the SMF, the NSACF and the GMLC enables NEF to configure a given Monitor Event at UDM, AMF, SMF, NSACF or GMLC and reporting of the event via UDM and/or AMF, SMF, NSACF or GMLC. Depending on the specific monitoring event or information, it is the AMF, GMLC, NSACF or the UDM that is aware of the monitoring event or information and makes it reported via the NEF.

The following table enumerates the monitoring events and their detection criteria:

Table 4.15.3.1-1: List of events for monitoring capability

Event	Detection criteria	Which NF detects the event
Loss of Connectivity	Network detects that the UE is no longer reachable for either signalling or user plane communication (see NOTE 4). The AF may provide a Maximum Detection Time, which indicates the maximum period of time without any communication with the UE after which the AF is to be informed that the UE is considered to be unreachable (see NOTE 7). If Unavailability Period Duration has been provided by the UE, the AMF uses the remaining value of it to determine the foreseen Loss of Connectivity time as described in clause 5.4.1.4 of TS 23.501 [2].	AMF
UE reachability	Detected when the UE transitions to CM-CONNECTED state or when the UE will become reachable for paging, e.g. Periodic Registration Update timer. It indicates when the UE becomes reachable for sending downlink data to the UE. The AF may provide the following parameters: 1) Maximum Latency; 2) Maximum Response Time; 3) Suggested number of downlink packets. (see NOTE 5 and NOTE 7). This event requires the Reachability Filter set to UE reachable for DL traffic" (see clause 5.2.2.3.1-1). For the usage of this event, see clauses 4.2.5.2 and 4.2.5.3. When requesting UE reachability monitoring, the AF may in addition request Idle Status Indication to be included in the UE reachability event reporting.	AMF, UDM
Location Reporting	This event is detected based on the Event Reporting Information Parameters that were received in the Monitoring Request (one-time reporting, maximum number of reports, maximum duration of reporting, periodicity, etc. as specified in clause 4.15.1). It reports either the Current Location or the Last Known Location of a UE. When AMF is the detecting NF: One-time and Continuous Location Reporting are supported. For Continuous Location Reporting the serving node(s) sends a notification every time it becomes aware of a location change, with the granularity depending on the accepted accuracy of location (see NOTE 1). For One-time Reporting with immediate reporting flag set, AMF reports the Last Known Location immediately. When AMF is the detecting NF: If the immediate reporting flag is not set, the AMF reports the UE Current Location (In case the AMF does not have the UE current location in the granularity as requested by the location report, the AMF retrieves the information via NG-RAN Location reporting procedure as defined in clause 4.10). When GMLC is the detecting NF: Immediate and Deferred Location Reporting is supported. For Deferred Location Reporting the event types UE availability, Area, Periodic Location and Motion are supported.	AMF, GMLC
Change of SUPI-PEI association	This event is detected when the association between PEI and subscription (SUPI) changes (USIM change).	UDM
Roaming status	This event is detected based on the UE’s current roaming status (the serving PLMN and/or whether the UE is in its HPLMN) and notification is sent when that status changes. (see NOTE 2). If the UE is registered via both 3GPP and N3GPP Access Type, then both instances of Roaming status are included.	UDM
Communication failure	This event is detected when RAN or NAS level failure is detected based on connection release and it identifies RAN/NAS release code.	AMF
Availability after Downlink Data Notification failure	This event is detected when the UE becomes reachable again after downlink data delivery failure. When requesting Availability after Downlink Data Notification failure monitoring, the AF may in addition request Idle Status Indication to be included in the UE reachability event reporting.	AMF
PDU Session Status	This event is detected when PDU session is established or released. (see NOTE 6)	SMF
Number of UEs present in a geographical area	This event is detected based on the Event Reporting Information Parameters that were received in the Monitoring Request (Level of aggregation, Sampling ratio, see clause 4.15.1). It indicates the number of UEs that are in the geographical area described by the AF. The AF may ask for the UEs that the system knows by its normal operation to be within the area (Last Known Location) or the AF may request the system to also actively look for the UEs within the area (Current Location).	AMF
CN Type change	The event is detected when the UE moves between EPC and 5GC. It indicates the current CN type for a UE or a group of UEs when detecting that the UE switches between being served by a MME and an AMF or when accepting the event subscription. (see NOTE 3)	UDM
Downlink data delivery status	It indicates the downlink data delivery status in the core network. Events are reported at the first occurrence of packets being buffered, transmitted or discarded, including: – Downlink data in extended buffering, including: – First data packet buffered event – Estimated buffering time, as per clause 4.2.3.3 – First downlink data transmitted event – First downlink data discarded event	SMF
UE reachability for SMS delivery	For SMS over NAS, this event is detected when an SMSF is registered for a UE and the UE is reachable as determined by the AMF and the UDM. For SMS over IP, the event is detected when the UE is reachable as determined by the AMF and the UDM regardless of an SMSF being registered. This enables the UE to receive an SMS. See clauses 4.2.5.2 and 4.2.5.3 (see NOTE 8).	UDM
UE memory available for SMS	This event is detected when the UE memory is available for SMS as determined by the AMF and the UDM. This enables to trigger Alert for SMS. See clause 5.1.8 of TS 23.540 [84]	UDM
Number of registered UEs or established PDU Sessions	It indicates the current number of registered UEs or established PDU Sessions for a network slice that is subject to NSAC. For One-time Reporting with Immediate Reporting Flag set, NSACF reports the number of registered UEs or established PDU Sessions immediately.	NSACF
Area Of Interest	It indicates change of the UE presence in the Area Of Interest.	AMF, GMLC
Group Member List Change	It indicates the changes on the members of the group. This event apply to a group of UEs (identified by an External Group ID), such as 5G VN group (see NOTE 9) or other groups.	UDM
Group-MBR monitoring	The bit rates of a set of specific QoS flows of a group of UEs’ PDU sessions are reported by the UEs’ respective serving PSA UPFs to NEF. The collected bit rates reported by UPFs are aggregated by the NEF. The aggregated bit rate is then compared against the AF provisioned Group-MBR threshold. If the aggregated bit rate exceeds the Group-MBR threshold, the NEF notifies the AF for such NEF event.	AF
NOTE 1: Location granularity for event request, or event report, or both could be at cell level (Cell ID) or TA level. The granularity can also be expressed by other formats such as geodetic uncertainty shapes (e.g. polygons, circles, etc.) or civic addresses (e.g. streets, districts, etc.) which can be mapped by NEF to AMF specific granularity levels. NOTE 2: Roaming status means whether the UE is in HPLMN or VPLMN based on the most recently received registration state in the UDM. NOTE 3: CN type of CN Type change event is defined in clause 5.17.5.1 of TS 23.501 [2]. NOTE 4: In the case of UDM service operation information flow, the UDM should set the subscribed periodic registration timer to a smaller value than the value of Maximum Detection Time, since the value of the mobile reachable timer is larger than the value of the periodic registration timer. NOTE 5: Maximum Latency, Maximum Response Time and Suggested number of downlink packets are defined in clause 4.15.6.3a. NOTE 6: The NEF makes a mapping between the 5GS internal event "PDU Session Status" and the T8 API event "PDN Connectivity Status". NOTE 7: The preferred method for provisioning Network Configuration Parameters is External Parameter Provisioning specified in clause 4.15.6.3a. Provisioning event specific parameters as part of Monitoring Request is expected to be used only by the AF that does not support Parameter Provisioning procedure specified in clause 4.15.6.3a. NOTE 8: The NEF maps between the T8 API event "UE reachability" with reachability type SMS and the 5GS internal event "UE reachability for SMS delivery" for SMS over NAS. The event "UE reachability for SMS delivery" for SMS over IP is used by HSS as described in clause 5.5.6.3 of TS 23.632 [68]. NOTE 9: 5G VN group management is defined in the clause 5.29.2 of TS 23.501 [2].

4.15.3.2 Information flows

4.15.3.2.1 AMF service operations information flow

The procedure is used by the NF to subscribe to notifications and to explicitly cancel a previous subscription. Cancelling is done by sending Namf_EventExposure_UnSubscribe request identifying Subscription Correlation ID. The notification steps 3 and 4 are not applicable in cancellation case.

Figure 4.15.3.2.1-1: Namf_EventExposure_Subscribe, Unsubscribe and Notify operations

1. A NEF sends a request to subscribe to a (set of) Event ID(s) in AMF in Namf_EventExposure_Subscribe request. The NEF could be the same NF subscribing to receive the event notification reports (i.e. Event Receiving NF) or it could be a different NF. The NEF subscribes to one or several Event(s) (identified by Event ID) and provides the associated notification endpoint of the Event Receiving NF. If the NEF itself is not the Event Receiving NF, the NEF shall additionally provide the notification endpoint of itself besides the notification endpoint of Event Receiving NF. Each notification endpoint is associated with the related (set of) Event ID(s). This is to assure the NEF can receive the notification of subscription change related event (e.g. Subscripiont Correlation ID Change).

Event Reporting information defines the type of reporting requested. If the reporting event subscription is authorized by the AMF, the AMF records the association of the event trigger and the requester identity.

2. AMF acknowledges the execution of Namf_EventExposure_Subscribe.

3. [Conditional – depending on the Event] The AMF detects the monitored event occurs and sends the event report by means of Namf_EventExposure_Notify message, to the notification endpoint of the Event Receiving NF.

4. [Conditional- depending on the Event] The AMF detects the subscription change related event occurs, e.g. Subscription Correlation ID change due to AMF reallocation, it sends the event report by means of Namf_EventExposure_Notify message to the NEF.

4.15.3.2.2 UDM service operations information flow

The procedure is used by the NEF to subscribe to event notifications, to modify group-based subscriptions to event notifications, including removal or addition of certain UEs in a UE group and to explicitly cancel a previous subscription (see clause 4.15.1). Cancelling is done by sending Nudm_EventExposure_Unsubscribe request identifying the subscription to cancel. The notification steps 4 and 5 are not applicable in cancellation case.

Figure 4.15.3.2.2-1: Nudm_EventExposure_Subscribe, Unsubscribe and Notify operations

1. The NEF subscribes to one or several monitoring events by sending Nudm_EventExposure_Subscribe request. The NEF subscribes to one or several Event(s) (identified by Event ID) and provides the associated notification endpoint of the NEF.

Event Reporting Information defines the type of reporting requested. If the reporting event subscription is authorized by the UDM, the UDM records the association of the event trigger and the requester identity.

The subscription may include Maximum number of reports and/or Maximum duration of reporting IE and optionally MTC Provider Information.

If subscription to group-based event notifications are removed for certain UEs in a group of UEs for which there is an event notification subscription, the NEF provides impacted UE information (e.g. SUPI, MSISDN or External Identity) and operation indication (cancellation) to UDM via Nudm_EventExposure_Subscribe without cancelling the entire group-based event notification subscription. If the Maximum Number of Reports applies to the event subscription, the NEF sets the stored number of reports of the indicated UE(s) to Maximum Number of Reports.

If subscription to group-based event notifications are added for certain UEs in a group of UEs for which there is an event notification subscription, the NEF provides impacted UE information (e.g. SUPI, MSISDN or External Identity) and operation indication (addition) to UDM via Nudm_EventExposure_Subscribe.

2a. [Conditional] Some events, require that UDM sends Namf_EventExposure_Subscribe request to the AMF serving that UE. As the UDM itself is not the Event Receiving NF, the UDM shall additionally provide the notification endpoint of itself besides the notification endpoint of NEF. Each notification endpoint is associated with the related (set of) Event ID(s). This is to assure the UDM can receive the notification of subscription change related event.

The UDM sends the Namf_EventExposure_Subscribe request to all serving AMF(s) (if subscription applies to a UE or a group of UE(s)), or to all the AMF(s) in the same PLMN as UDM (if subscription applies to any UE). The UDM stores the subscription even if the target UE or group member UE is not registered at the time of subscription.

NOTE 1: If the single target UE, or group member UE, registers later on with an AMF which does not have event subscription or group event subscription(s) for that UE or UE group, then the UDM creates subscriptions to those event(s) with the AMF during the Registration procedure as specified in clause 4.2.2.2.2.

If the subscription applies to a group of UE(s), the UDM shall include the same notification endpoint of itself, i.e. Notification Target Address (+ Notification Correlation Id), in the subscriptions to all UE’s serving AMF(s).

NOTE 2: The same notification endpoint of UDM is to help the AMF identify whether the subscription for the requested group event is same or not when a new group member UE is registered.

If Nudm_EventExposure_Subscribe with update is received in step 1 indicating removal of event notification subscription for certain UEs in a group of UEs for which there is an event notification subscription, the UDM provides impacted UE information (e.g. SUPI, MSISDN) and operation indication (cancellation) to AMF via Namf_EventExposure_Subscribe without cancelling the entire group-based event notification subscription, for the event monitored by AMF.

If Nudm_EventExposure_Subscribe with update is received in step 1 indicating addition of event notification subscription for certain UEs in a group of UEs for which there is an event notification subscription, the UDM provides impacted UE information (e.g. SUPI, MSISDN) and operation indication (addition) to AMF via Namf_EventExposure_Subscribe for the event monitored by AMF.

2b. [Conditional] AMF acknowledges the execution of Namf_EventExposure_Subscribe.

3. UDM acknowledges the execution of Nudm_EventExposure_Subscribe.

If the subscription is applicable to a group of UE(s) and the Maximum number of reports is included in the Event Report information in step 1, the Number of UEs (including all group member UEs irrespective of their registration state) within this group is included in the acknowledgement. If AMF provides the first event report in step 2b, the UDM includes the event report in the acknowledgement.

4a – 4b. [Conditional – depending on the Event] The UDM detects the monitored event occurs and sends the event report, by means of Nudm_EventExposure_Notify message, to the associated notification endpoint of the NEF, along with the time stamp. NEF may store the information in the UDR along with the time stamp using either Nudr_DM_Create or Nudr_DM_Update service operation as appropriate.

If Nudm_EventExposure_Subscribe with update is received in step 1 indicating removal of event notification subscription for certain UEs in a group of UEs for which there is an event notification subscription, the UDM shall stop the event notification for the impacted UEs. If Maximum number of Reports is applied, the UDM shall set the number of reports of the indicated UE(s) to Maximum Number of Reports for the events monitored by UDM.

If Nudm_EventExposure_Subscribe with update is received in step 1 indicating addition of event notification subscription for certain UEs in a group of UEs for which there is an event notification subscription, the UDM shall create subscription to the event notification for the impacted UEs so as to detect the monitored event and send the event report for such impacted UEs.

4c – 4d. [Conditional – depending on the Event] The AMF detects the monitored event occurs and sends the event report, by means of Namf_EventExposure_Notify message, to the associated notification endpoint of the NEF, along with the time stamp. NEF may store the information in the UDR along with the time stamp using either Nudr_DM_Create or Nudr_DM_Update service operation as appropriate.

If the AMF has a maximum number of reports stored for the UE, the AMF shall decrease its value by one for the reported event.

If Namf_EventExposure_Subscribe with update is received in step 2a indicating removal of event notification subscription for certain UEs in a group of UEs for which there is an event notification subscription, the AMF shall stop the event notifications for the impacted UEs. If Maximum number of Reports is applied, the AMF shall set the number of reports of the indicated UE(s) to Maximum Number of Reports.

If Namf_EventExposure_Subscribe with update is received in step 2a indicating addition of event notification subscription for certain UEs in a group of UEs for which there is an event notification subscription, the AMF shall create subscription to the event notification for the impacted UEs so as to detect the monitored event and send the event report for such impacted UEs.

For both step 4a and step 4c, when the maximum number of reports is reached and if the subscription is applied to a UE, The NEF unsubscribes the monitoring event(s) to the UDM and the UDM unsubscribes the monitoring event(s) to AMF serving that UE.

For both step 4a and step 4c, when the maximum number of reports is reached for an individual group member UE, the NEF uses the Number of UEs received in step 3 and the Maximum number of reports to determine if reporting for the group is complete. If the NEF determines that reporting for the group is complete, the NEF unsubscribes the monitoring event(s) to the UDM and the UDM unsubscribes the monitoring event(s) to all AMF(s) serving the UEs belonging to that group.

NOTE 3: If an expiry time as specified in clause 6.2.6.2.6 of TS 29.518 [18] is not included in the event subscription, then the life time of the event subscription needs to be controlled by other means as there is no time based cancellation at all even if any group member UEs fail to register.

When the Maximum duration of reporting expires in the NEF, the UDM and the AMF, then each of these nodes shall locally unsubscribe the monitoring event.

5. [Conditional – depending on the Event] The AMF detects the subscription change related event occurs, e.g. Subscription Correlation ID change due to AMF reallocation or addition of new Subscription Correlation ID due to a new group UE registered, it sends the event report by means of Namf_EventExposure_Notify message to the associated notification endpoint of the UDM.

4.15.3.2.3 NEF service operations information flow

The procedure is used by the AF to subscribe to event notifications, to modify group-based subscriptions to event notification and to explicitly cancel a previous subscription (see clause 4.15.1). Cancelling is done by sending Nnef_EventExposure_Unsubscribe request identifying the subscription to cancel with Subscription Correlation ID. The notification steps 6 to 8 are not applicable in cancellation case.

Figure 4.15.3.2.3-1: Nnef_EventExposure_Subscribe, Unsubscribe and Notify operations

1. The AF subscribes to one or several Event(s) (identified by Event ID) and provides the associated notification endpoint of the AF by sending Nnef_EventExposure_Subscribe request.

Event Reporting Information defines the type of reporting requested (e.g. one-time reporting, periodic reporting or event based reporting, for Monitoring Events). If the reporting event subscription is authorized by the NEF, the NEF records the association of the event trigger and the requester identity. The subscription may also include Maximum number of reports and/or Maximum duration of reporting IE and optionally MTC Provider Information.

If subscription to group-based event notifications are removed or added for certain UEs in a group of UEs for which there is an event notification subscription, the AF provides impacted UE information (e.g. SUPI, MSISDN or External Identity) with operation indication which is either cancellation or addition to NEF via Nnef_EventExposure_Subscribe without cancelling the entire group-based event notification subscription.

2. [Conditional – depending on authorization in step 1] The NEF subscribes to received Event(s) (identified by Event ID) and provides the associated notification endpoint of the NEF to UDM by sending Nudm_EventExposure_Subscribe request. The NEF may either receive DNN, S-NSSAI from AF in step 1 or maps the AF-Identifier into DNN and S-NSSAI combination based on local configuration and include DNN, S-NSSAI in the request.

If the reporting event subscription is authorized by the UDM, the UDM records the association of the event trigger and the requester identity. Otherwise, the UDM continues in step 4 indicating failure.

If Nnef_EventExposure_Subscribe with update is received in step 1 indicating removal of event notification subscription for certain UEs in a group of UEs for which there is an event notification subscription, the NEF provides impacted UE information (e.g. SUPI, MSISDN or External Identity) with operation indication (cancellation) to UDM via Nudm_EventExposure_Subscribe without cancelling the entire group-based event notification subscription. If the Maximum Number of Reports applies to the event subscription, the NEF sets the stored number of reports of the indicated UE(s) to Maximum Number of Reports.

If Nnef_EventExposure_Subscribe with update is received in step 1 indicating addition of event notification subscription for certain UEs in a group of UEs for which there is an event notification subscription, the NEF provides impacted UE information (e.g. SUPI, MSISDN or External Identity) with operation indication (addition) to UDM via Nudm_EventExposure_Subscribe.

3a. [Conditional] If the requested event (e.g. monitoring of Loss of Connectivity) requires AMF assistance, then the UDM sends the Namf_EventExposure_Subscribe to the AMF serving the requested user. The UDM sends the Namf_EventExposure_Subscribe request to the all serving AMF(s) (if subscription applies to a UE or a group of UE(s)), or all the AMF in the same PLMN as the UDM (if subscription applies to any UE).

NOTE 1: If the UE, which is a member of a group, registers with an AMF which does not have group event subscription(s) for that group, then the UDM creates subscriptions to those event(s) with the AMF during the Registration procedure in clause 4.2.2.2.2.

As the UDM itself is not the Event Receiving NF, the UDM shall additionally provide the notification endpoint of itself besides the notification endpoint of NEF. Each notification endpoint is associated with the related (set of) Event ID(s). This is to assure the UDM can receive the notification of subscription change related event.

NOTE 2: The same notification endpoint of UDM is to help the AMF identify whether the subscription for the requested group event is same or not when a new group member UE is registered.

If Nudm_EventExposure_Subscribe with update is received in step 2 indicating removal of event notification subscription for certain UEs in a group of UEs for which there is an event notification subscription, the UDM provides impacted UE information (e.g. SUPI, MSISDN) with operation indication (cancellation) to AMF via Namf_EventExposure_Subscribe without cancelling the entire group-based event notification subscription, for the event monitored by AMF.

If Nudm_EventExposure_Subscribe with update is received in step 2 indicating addition of event notification subscription for certain UEs in a group of UEs for which there is an event notification subscription, the UDM provides impacted UE information (e.g. SUPI, MSISDN) with operation indication (addition) to AMF via Namf_EventExposure_Subscribe for the event monitored by AMF.

3b. [Conditional] AMF acknowledges the execution of Namf_EventExposure_Subscribe.

3c. [Conditional] If the requested event (e.g. PDU Session Status) requires SMF assistance, then the UDM sends the Nsmf_EventExposure_Subscribe Request message to each SMF where at least one UE identified in step 2 has a PDU session established. The NEF notification endpoint received in step 2 is included in the message.

NOTE 3: In the home routed case, the UDM sends the subscription to the V-SMF via the H-SMF.

3d. [Conditional] The SMF acknowledges the execution of Nsmf_EventExposure_Subscribe.

4. [Conditional] UDM acknowledges the execution of Nudm_EventExposure_Subscribe.

If the subscription is applicable to a group of UE(s) and the Maximum number of reports is included in the Event Report information in step 1, the Number of UEs (including all group member UEs irrespective of their registration state) is included in the acknowledgement. If AMF or SMF provides the first event report in step 3b or step 3d, the UDM includes the event report in the acknowledgement.

5. NEF acknowledges the execution of Nnef_EventExposure_Subscribe to the requester that initiated the request. If the NEF has received the first event report already in step 4, the NEF includes the event report in the acknowledgement.

6a – 6b. [Conditional – depending on the Event] The UDM (depending on the Event) detects the event occurs and sends the event report, by means of Nudm_EventExposure_Notify message to the associated notification endpoint of the NEF along with the time stamp. NEF may store the information in the UDR along with the time stamp using either Nudr_DM_Create or Nudr_DM_Update service operation as appropriate.

If Nudm_EventExposure_Subscribe with update is received in step 2 indicating removal of event notification subscription for certain UEs in a group of UEs for which there is an event notification subscription, the UDM shall stop the event notification for the impacted UEs. If Maximum number of Reports is applied, the UDM shall set the number of reports of the indicated UE(s) to Maximum Number of Reports for the events monitored by UDM.

If Nudm_EventExposure_Subscribe with update is received in step 2 indicating addition of event notification subscription for certain UEs in a group of UEs for which there is an event notification subscription, the UDM shall create subscription to the event notification for the impacted UEs so as to detect the monitored event and send the event report for such impacted UEs.

6c – 6d. [Conditional – depending on the Event] The AMF detects the event occurs and sends the event report, by means of Namf_EventExposure_Notify message to associated notification endpoint of the NEF along with the time stamp. NEF may store the information in the UDR along with the time stamp using either Nudr_DM_Create or Nudr_DM_Update service operation as appropriate.

If the AMF has a maximum number of reports stored for the UE or the individual member UE, the AMF shall decrease its value by one for the reported event.

If Namf_EventExposure_Subscribe with update is received in step 3a indicating removal of event notification subscription for certain UEs in a group of UEs for which there is an event notification subscription, the AMF shall stop the event notification for the impacted UEs. If Maximum number of Reports is applied, the AMF shall set the number of reports of the indicated UE(s) to Maximum Number of Reports.

If Namf_EventExposure_Subscribe with update is received in step 3a indicating addition of event notification subscription for certain UEs in a group of UEs for which there is an event notification subscription, the AMF shall create subscription to the event notification for the impacted UEs so as to detect the monitored event and send the event report for such impacted UEs.

For both step 6a and step 6c, when the maximum number of reports is reached and if the subscription is applied to a UE, The NEF unsubscribes the monitoring event(s) to the UDM and the UDM unsubscribes the monitoring event(s) to AMF serving for that UE.

For both step 6a and step 6c, when the maximum number of reports is reached for an individual group member UE, the NEF uses the Number of UEs received in step 4 and the Maximum number of reports to determine if reporting for the group is complete. If the NEF determines that reporting for the group is complete, the NEF unsubscribes the monitoring event(s) to the UDM and the UDM unsubscribes the monitoring event(s) to all AMF(s) serving the UEs belonging to that group.

NOTE 4: If an expiry time as specified in clause 6.2.6.2.6 of TS 29.518 [18] is not included in the event subscription, then the life time of the event subscription needs to be controlled by other means as there is no time based cancellation at all even if any group member UEs fail to register.

When the Maximum duration of reporting expires in the NEF, the UDM and the AMF, then each of these nodes shall locally unsubscribe the monitoring event.

6e – 6f. [Conditional – depending on the Event] When the SMF detects a subscribed event, the SMF sends the event report, by means of Nsmf_EventExposure_Notify message, to the associated notification endpoint of the NEF provided in step 3c. NEF may store the information in the UDR along with the time stamp using either Nudr_DM_Create or Nudr_DM_Update service operation as appropriate.

7. [Conditional – depending on the Event in steps 6a-6f] The NEF forwards to the AF the reporting event received by either Nudm_EventExposure_Notify and/or Namf_EventExposure_Notify. In the case of the PDU Session Status event, the NEF maps it to an PDN Connectivity Status notification when reporting to the AF.

8. [Conditional – depending on the Event] The AMF detects the subscription change related event occurs, e.g. Subscription Correlation ID change due to AMF reallocation or addition of new Subscription Correlation ID due to a new group UE registered, it sends the event report, by means of Namf_EventExposure_Notify message to the associated notification endpoint of the UDM.

4.15.3.2.3a Void

4.15.3.2.3b Specific NEF service operations information flow for loss of connectivity and UE reachability

The procedure is used by the AF to subscribe to notifications and to explicitly cancel a previous subscription for loss of connectivity and UE reachability.

Figure 4.15.3.2.3b-1: Nnef_EventExposure_Subscribe, Unsubscribe and Notify operations or loss of connectivity and UE reachability

1. Step 1 to step 3b of Figure 4.15.3.2.3-1 are performed with the following differences:

– For Loss of Connectivity, the subscription request may include Maximum Detection Time (see Table 4.15.3.1-1).

– For UE reachability, the subscription request may include Maximum Latency, Maximum Response Time and/or Suggested number of downlink packets (see Table 4.15.3.1-1). In step 3a of Figure 4.15.3.2.3-1, the UDM may include Maximum Response Time in the subscription request to the AMF.

NOTE 1: It is expected that Maximum Latency, Maximum Response Time and/or Suggested number of downlink packets included in the subscription request is only used by the AF that does not support Parameter Provisioning procedure specified in clause 4.15.6.3a.

– For UE reachability, the AF may include Idle Status Indication request. If Idle Status Indication request is included, the NEF includes it in Nudm_EventExposure_Subscribe message. If the UDM receives Idle Status Indication request, it includes it in Namf_EventExposure_Subscribe message. If the NEF does not support the requested Idle Status Indication, then depending on operator policies, the NEF rejects the request.

2. [Conditional] If the subscribed periodic registration timer has not been set according to any subscription request, or a Network Configuration as defined in clause 4.15.6.3a the UDM shall set the subscribed periodic registration timer using the Maximum Detection Time or Maximum Latency; otherwise if the subscribed periodic registration timer was previously set by a different subscription identified by a different Notification Target Address (+ Notification Correlation ID), or set by a different Network Configuration identified by a different NEF reference ID for the same UE and if the newly received Maximum Detection Time or Maximum Latency is lower than the provided subscribed periodic registration timer, the UDM shall set the subscribed periodic registration timer using the newly received Maximum Detection Time or Maximum Latency.

If Nudm_EventExposure_Unsubscribe request is performed in step 1, the UDM shall recalculate the subscribed periodic registration timer based on the remaining event subscriptions and/or Network Configurations.

In addition for UE reachability subscription, if the newly received Maximum Response Time is longer than the provided subscribed Active Time (i.e. previously provided Maximum Response Time), the UDM shall set the subscribed Active Time using the newly received Maximum Response Time. If the suggested number of downlink packets is newly received, the UDM shall add the newly received suggested number of downlink packets to the currently used value of suggested number of downlink packets if the aggregated value is within the operator defined range.

If Nudm_EventExposure_Unsubscribe request is performed in step 1, the UDM shall recalculate the subscribed Active Time and/or Suggested Number of Downlink Packets based on the remaining event subscriptions and/or Network Configurations.

If the subscribed periodic registration timer or the subscribed Active Time are set or modified, the UDM sends the Nudm_SDM_Notification request to related serving AMF(s). If the AMF receives a subscribed periodic registration timer value from the UDM, it allocates the received value to the UE as the periodic registration timer at subsequent Registration procedure. The AMF starts monitoring of the expiration of the mobile reachable timer for Loss of Connectivity (if required) and starts monitoring of the UE entering connected mode for UE reachability (if required).

If the suggested number of downlink packets are set or modified, the UDM sends the Nudm_SDM_Notification request to related serving SMF(s). The SMF configures the data buffer at the SMF/UPF according the suggested number of downlink packets.

If the provided value is updated by the UDM, the UDM may notify the NEF (which then notifies the AF) of the actual value that is being applied in the 3GPP network.

3. Step 4 to step 5 of Figure 4.15.3.2.3-1 are performed.

4. Step 6c to step 6d of Figure 4.15.3.2.3-1 are performed with the following differences:

– For Loss of Connectivity, the event is detected when the mobile reachability timer expires or when the UE has provided Unavailability Period Duration during the Registration or Deregistration procedure as described in clause 5.4.1.4 of TS 23.501 [2].

– For UE reachability, the event is detected when the UE changes to connected mode or when the UE will become reachable for paging.

– For UE reachability, if Idle Status Indication request was included in step 1 and the AMF supports Idle Status Indication, the AMF includes also the Idle Status Indication.

5. Step 8 of Figure 4.15.3.2.3-1 is performed.

4.15.3.2.3c Specific NEF service operations information flow for group member list change

The procedure is used by the AF to subscribe to notifications and to explicitly cancel a previous subscription for group member list change.

Step 1, step 2, step 4, step 5, step 6a and step 7 of Figure 4.15.3.2.3-1 are performed with the differences that the Event ID is set with "Group Member List Change". When a NF consumer subscribes to the group member list change event, if the request indicates immediate reporting, the group member list is provided in the Nudm/Nnef_EeventEExposure_Subscribe response,

When the UDM detects the group member list change event occurs, it sends the event report including the identities of the UE(s) added/removed to/from the group to the NEF by means of Nudm_EventExposure_Notify message, and NEF forwards the information to the AF by means of Nnef_EventExposure_Notify message.

4.15.3.2.4 Exposure with bulk subscription

Based on operator configuration NEF may perform bulk subscription with the NFs that provides necessary services. This feature is controlled by local policies of the NEF that control which events (set of Event ID(s)) and UE(s) are target of a bulk subscription.

When the NEF performs bulk subscription (subscribes for any UE (i.e. all UEs), group of UE(s) (e.g. identifying a certain type of UEs such as IoT UEs)), it subscribes to all the NFs that provide the necessary services (e.g. In a given PLMN, NEF may subscribe to all AMFs that support reachability notification for IoT UEs). Upon receiving bulk subscription from the NEF, the NFs store this information. Whenever the corresponding event(s) occur for the requested UE(s) as in bulk subscription request, NFs notify the NEF with the requested information.

The following call flow shows how network exposure can happen for one UE, groups of UE(s) (e.g. identifying a certain type of UEs such as IoT UEs) or any UE.

Figure 4.15.3.2.4-1: NF registration/status notification and Exposure with bulk subscription

1. NEF registers with the NRF for any newly registered NF along with its NF services.

2. When an NF instantiates, it registers itself along with the supported NF services with the NRF.

3. NRF acknowledges the registration

4. NRF notifies the NEF with the newly registered NF along with the supported NF services.

5. NEF evaluates the NF and NF services supported against the pre-configured events within NEF. Based on that, NEF subscribes with the corresponding NF either for a single UE, group of UE(s) (e.g. identifying a certain type of UEs such as IoT UEs), any UE. NF acknowledges the subscription with the NEF.

6 – 7. When the event trigger happens, NF notifies the requested information towards the subscribing NEF along with the time stamp. NEF may store the information in the UDR along with the time stamp using either Nudr_DM_Create or Nudr_DM_Update service operation as appropriate.

8. Application registers with the NEF for a certain event identified by event filters. If the registration for the event is authorized by the NEF, the NEF records the association of the event and the requester identity.

9 – 10. When the event trigger happens, NF notifies the requested information towards the subscribing NEF. NEF may store the information in the UDR using either Nudr_DM_Create or Nudr_DM_Update service operation as appropriate.

11a-b. NEF reads from UDR with Nudr_DM_Query and notifies the application along with the time stamp for the corresponding subscribed events.

4.15.3.2.5 Information flow for downlink data delivery status with SMF buffering

The procedure is used if the SMF requests the UPF to forward downlink data packets that are subject of extended buffering in the SMF. The procedure describes a mechanism for the Application Function to subscribe downlink data delivery status notifications. The downlink data delivery status notifications relates to high latency communication, see also clauses 4.24.2 and 4.2.3.3.

Cancelling the subscription is done by sending Nnef_EventExposure_Unsubscribe request identifying the subscription to cancel with Subscription Correlation ID in the same order as indicated in figure 4.15.3.2.5-1 for the corresponding subscribe requests. Step 0 and the notification steps 7 to 9 are not applicable in cancellation case.

Figure 4.15.3.2.5-1: Information flow for downlink data delivery status with SMF buffering

0. The SMF (in the non-roaming case the SMF, in the roaming case the V-SMF, in the case of PDU session with I-SMF the I-SMF) configures the relevant UPF to forward downlink data packets towards the SMF as described in clause 5.8.3 in 23.501 [2]. The SMF decides to apply this behaviour based on the "expected UE behaviour". Alternatively, step 0 is triggered by step 3,

1. The AF sends Nnef_EventExposure_Subscribe Request to NEF requesting notification for event "Downlink data delivery status" with traffic descriptor (e.g. the source of the downlink IP or Ethernet traffic) for a UE or group of UEs. If the reporting event subscription is authorized by the NEF, the NEF records the association of the event trigger and the requester identity. The Downlink data delivery status events include:

– First downlink Packet in extended buffering event:

– This event is triggered when the first new downlink data packet is buffered with extended buffering matching the traffic descriptor.

– in notifications about this Downlink data delivery status, the SMF provides the Extended Buffering time as determined in clause 4.2.3.3.

– First downlink Packet discarded:

– This event occurs when the first packet matching the traffic descriptor is discarded because the Extended Buffering time, as determined by the SMF, expires or the amount of downlink data to be buffered is exceeded.

– First Downlink Packet transmitted:

– This event occurs when the first packet matching the traffic descriptor is transmitted after previous buffering or discarding of corresponding packet(s) because the UE of the PDU Session becomes ACTIVE and buffered data can be delivered to UE according to clause 4.2.3.3.

2. The NEF sends the Nudm_EventExposure_Subscribe Request to UDM. Identifier of the UE or group of UEs, the traffic descriptor, monitoring event received from AF in step 1 and notification endpoint of the NEF are included in the message. If the reporting event subscription is authorized by the UDM, the UDM records the association of the event trigger and the requester identity. Otherwise, the UDM continues in step 5 indicating failure.

3. The UDM sends the Nsmf_EventExposure_Subscribe Request message to each SMF where at least one UE identified in step 2 has a PDU session established. If the UDM is able to derive the applicable DNN and S-NSSAI from the traffic descriptor via configured information, the UDM may send Nsmf_EventExposure_Subscribe Request messages only to SMFs with PDU sessions with that DNN and S-NSSAI for such UEs and includes the Identifier of the UE or Internal-Group-Id, traffic descriptor, monitoring event and the notification endpoint of NEF received in step 2 are included in the message. If the UDM becomes aware that such a UE has a PDU session established with the DNN and S-NSSAI corresponding to the traffic descriptor at a later time than when receiving step 2, the UDM then executes step 3.

In the case of home-routed PDU session or PDU session with I-SMF, the UDM sends the Nsmf_EventExposure_Subscribe Request message to each H-SMF or SMF and the H-SMF or SMF further sends Nsmf_EventExposure_Subscribe Request message to each related V-SMF or I-SMF. Steps 7-8 are performed by V-SMF or I-SMF.

4. The SMF sends the Nsmf_EventExposure_Subscribe Response message to the UDM.

5. The UDM send sends the Nsmf_EventExposure_Subscribe response message to the NEF.

6. The NEF sends the Nsmf_EventExposure_Subscribe response to the AF.

7. The SMF detects a change in Downlink Data Delivery Status event as described in clause 4.2.3. The SMF becomes aware that Downlink Packet(s) require extended buffering via a Namf_Communication_N1N2MessageTransfer service operation with the AMF. If the SMF decides to discard packets, the "Downlink Packet(s) discarded event" is detected. The SMF detects that previously buffered packets can be transmitted by the fact that the related PDU session becomes ACTIVE.

8. The SMF sends the Nsmf_EventExposure_Notify with Downlink Delivery Status event message to NEF.

9. The NEF sends Nnef_EventExposure_Notify with Downlink Delivery Status event message to AF.

4.15.3.2.6 GMLC service operations information flow

The procedure is used by the NF to subscribe to notifications and to explicitly cancel a previous subscription. The GMLC service operations information flow is defined in clause 6.1.2 and clause 6.3 of TS 23.273 [51].

4.15.3.2.7 Information flow for Availability after DDN Failure with SMF buffering

The procedure is used if the SMF requests the UPF to forward packets that are subject of buffering in the SMF. The procedure describes a mechanism for the Application Function to subscribe to notifications about availability after downlink data notification failure. The Availability after Downlink Data Notification failure event is related to high latency communication, see also clauses 4.24.2 and 4.2.3.3.

Cancelling the subscription is done by sending EventExposure_Unsubscribe requests identifying the subscription to cancel with the Subscription Correlation ID in the same order as indicated in figure 4.15.3.2.7-1 for the corresponding subscribe requests (the AMF unsubscribes the DDN Failure status notification by sending the Nsmf_PDUSession_UpdateSMContext Request message to each SMF in step 5). Step 0 and the notification steps 9 to 13 are not applicable in the cancellation case.

Figure 4.15.3.2.7-1: Information flow for availability after DDN Failure with SMF buffering

0. The SMF (in the no-roaming case the H-SMF. in the roaming case the V-SMF, in the case of PDU session with I-SMF the I-SMF) configures the relevant UPF to forward packets to the SMF as described in clause 5.8.3 in 23.501 [2]. The SMF decides to apply this behaviour based on the "expected UE behaviour". Alternatively, step 0 is triggered by step 5.

1. The AF sends Nnef_EventExposure_Subscribe Request to the NEF requesting notifications for "Availability after DDN Failure" for a UE or group of UEs and providing a traffic descriptor identifying the source of the downlink IP or Ethernet traffic. If the reporting event subscription is authorized by the NEF, the NEF records the association of the event trigger and the requester identity.

The AF may include Idle Status Indication request in the Nnef_EventExposure_Subscribe Request. If Idle Status Indication request is included, the NEF includes it in Nudm_EventExposure_Subscribe message. If the NEF does not support the requested Idle Status Indication, then depending on operator policies, the NEF rejects the request.

2. The NEF sends the Nudm_EventExposure_Subscribe Request to UDM. Identifier of the UE or group of UEs, the traffic descriptor, monitoring event received from AF at step 1 and notification endpoint of the NEF are included in the message. If the reporting event subscription is authorized by the UDM, the UDM records the association of the event trigger and the requester identity. Otherwise, the UDM continues in step 7 indicating failure.

If the UDM receives Idle Status Indication request, it includes it in Namf_EventExposure_Subscribe message.

3. The UDM sends Namf_EventExposure_Subscribe messages to the AMF(s) which serve the UE(s) identified in step2 to subscribe to "Availability after DDN Failure". The UDM includes the DNN and S-NSSAI as well as the Traffic Descriptor if available A separate subscription is used for each UE. The NEF notification endpoint received in step 2 is included in the message. If the UDM becomes aware that such a UE is registered at a later time than when receiving step 2, the UDM then executes step 3.

4. The AMF acknowledges the execution of Namf_EventExposure_Subscribe.

5. If PDU Session exists for the DNN and S-NSSAI, the AMF subscribes to DDN Failure status notification by sending the Nsmf_PDUSession_UpdateSMContext Request message to each SMF, requesting the SMF to notify DDN Failure. The AMF also includes in Nsmf_PDUSession_UpdateSMContext the Traffic Descriptor and NEF correlation ID if received from the UDM. For new PDU Session establishment towards a DNN and S-NSSAI, the AMF subscribes to DDN Failure status notification in Nsmf_PDUSession_CreateSMContext Request message if the UDM has subscribed to Availability after DDN Failure event.

In the case of home-routed PDU session or PDU session with I-SMF, the AMF sends Nsmf_PDUSession_UpdateSMContext Request message(s) to the related V-SMF(s) or I SMF(s). Steps 9-10 are performed by those V-SMF(s) or I-SMF(s).

6. The (I/V-)SMF sends the Nsmf_PDUSession_UpdateSMContext response message to the AMF.

NOTE: Step 7 can happen any time after step 4.

7. The UDM sends the Nudm_EventExposure_Subscribe response to the NEF.

8. The NEF sends the Nsmf_EventExposure_Subscribe response to the AF.

9-10. The SMF is informed that the UE is unreachable via a Namf_Communication_N1N2MessageTransfer service operation. The SMF then decides to discard downlink packets received from the UPF. By comparing those discarded downlink packets received from the UPF with the Traffic Descriptor(s) received in the event subscription(s), the SMF determines whether DDN Failure due to any traffic from an AF is to be notified to the AMF and if so, the SMF sends the DDN Failure status, by means of Nsmf_PDUSession_SMContextStatusNotify message including NEF Correlation ID, to the AMF. If the UE is not reachable after the AMF received the DDN Failure notification from the SMF, the AMF shall set a Notify-on-available-after-DDN-failure flag corresponding to the NEF Correlation ID.

11-12. [Conditional] The AMF detects the UE is reachable and sends the event report(s) based on the Notify-on-available-after-DDN-failure flag, by means of Namf_EventExposure_Notify message(s), only to the NEF(s) indicated as notification endpoint(s) identified via the corresponding subscription in step 3. In this way, only the AF(s) for which DL traffic transmission failed are notified.

If the AMF received Idle Status Indication request in step 3 and the AMF supports Idle Status Indication, the AMF includes also the Idle Status Indication.

13. The NEF sends Nnef_EventExposure_Notify message with the "Availability after DDN Failure" event to AF.

4.15.3.2.8 Information flow for downlink data delivery status with UPF buffering

The procedure is used if the SMF requests the UPF to buffer packets. The procedure describes a mechanism for the Application Function to subscribe to notifications about downlink data delivery status. The downlink data delivery status notifications relates to high latency communication, see also clauses 4.24.2 and 4.2.3.3.

Cancelling is done by sending Nnef_EventExposure_Unsubscribe request identifying the subscription to cancel with Subscription Correlation ID. Steps 2 to 5 are not applicable in the cancellation case.

Figure 4.15.3.2.8-1: Information flow for downlink data delivery status with UPF buffering

1. AF interacts with NEF to subscribe DDD status event in SMF as described in steps 0-6 of clause 4.15.3.2.5.

In the case of subscription cancelling and SMF having interacted with the PCF during event subscription, the SMF reports to the PCF the unsubscribe of the DDD status event. The PCF updates or removes the PCC rule and this triggers the SMF to update or remove the corresponding PDR in the UPF. In case of home-routed PDU Session, the SMF unsubscribes the DDD status event from the V-SMF which in turn updates the N4 information (deactivating the notifications) in the V-UPF. In case of PDU Session with I-SMF, the SMF provides updated N4 information (deactivating the notifications) to the I-SMF which in turn updates the I-UPF.

2. If the UPF is configured to apply extended buffering, step 2 is executed immediately after step 1. Otherwise, step 2 is executed when the SMF is informed that the UE is unreachable via a Namf_Communication_N1N2MessageTransfer service operation as described in clause 4.2.3 and the SMF then also updates the PDR(s) for flows requiring extended buffering to requests the UPF to buffer downlink packets. If the DDD status event with traffic descriptor has been received in the SMF in step 1, if extended DL Data buffering in the UPF applies, the SMF checks whether an installed PDR for the Traffic Descriptor exists and if so, requests the UPF to provide the requested type(s) of notifications. If PCC is not used and there is no installed PDR with the exact same traffic descriptor, the SMF copies the installed PDR that would have previously matched the incoming traffic described by the traffic descriptor, but provides that traffic descriptor, a higher priority and the requested type(s) of notifications. If PCC is used and if the "DDD Status event subscription with Traffic Descriptor" PCRT is set as defined in clause 6.1.3.5 of TS 23.503 [20], the SMF interacts with the PCF and forwards the traffic descriptor before contacting the UPF; the PCF then updates an existing PCC rule or provides a new PCC rule taking into consideration the traffic descriptor for the subscribed DDD status event.

NOTE: If a new PCC rule is provided by the PCF for the DDD status event detection, the PCF populates the PCC rules as defined in clause 6.1.3.5 of TS 23.503 [20].

In the case of home-routed PDU Session, the V-SMF generates the N4 information (activating the notifications) for the V-UPF based on local configuration.

In the case of PDU Session with I-SMF, the SMF provides N4 information (activating the notifications) to the I-SMF based on local policy or the "DDD Status event subscription with Traffic Descriptor" PCRT from PCF. The I-SMF updates the I-UPF with this N4 information.

For home-routed PDU Session or PDU Session with I-SMF, steps 3-4 below are performed by V-SMF/V-UPF or I-SMF/I-UPF.

3. The UPF reports when there is buffered or discarded traffic matching the received PDR to the SMF. The SMF detects that previously buffered packets can be transmitted by the fact that the related PDU session becomes ACTIVE.

4. The SMF sends the Nsmf_EventExposure_Notify with Downlink Delivery Status event message to NEF.

5. The NEF sends Nnef_EventExposure_Notify with Downlink Delivery Status event message to AF.

4.15.3.2.9 Information flow for Availability after DDN Failure with UPF buffering

The procedure is used if the SMF requests the UPF to buffer packets. The procedure describes a mechanism for the Application Function to subscribe to notifications about availability after DDN failure.

Cancelling is done by sending Nnef_EventExposure_Unsubscribe request identifying the subscription to cancel with Subscription Correlation ID. Steps 2 to 7 are not applicable in the cancellation case.

Figure 4.15.3.2.9-1: Information flow for availability after DDN Failure event with UPF buffering

1. AF interacts with NEF to subscribe availability after DDN failure event in AMF/SMF as described in steps 0-8 of clause 4.15.3.2.7.

In case of subscription cancelling from AMF and SMF having interacted with the PCF during event subscription, the SMF reports to the PCF for the unsubscribe of DDN failure event. The PCF updates or removes the PCC rule and this triggers the SMF to update or remove the corresponding PDR and FAR in the UPF.

In the case of PDU Session with I-SMF or home-routed PDU Session, the AMF unsubscribes the DDN failure event towards I/V-SMF. In case of home-routed PDU Session, the V-SMF updates the N4 information (deactivating the notifications) in the V-UPF. In case of PDU Session with I-SMF, the I-SMF may request N4 information (deactivating the notifications) from the SMF and provides the Traffic Descriptor to the SMF. The SMF provides updated N4 information (deactivating the notifications) to the I-SMF which in turn updates the I‑UPF.

2. The SMF checks whether an installed PDR for the Traffic Descriptor exists and if so, requests the UPF to report when the first downlink packet is received and when it is discarded in the UPF. If PCC is not used and there is no installed PDR with the exact same traffic descriptor, the SMF copies the installed PDR that would have previously matched the incoming traffic described by the traffic descriptor, but provides that traffic descriptor, a higher priority and requests the UPF to report when the first downlink packet is received and when it is discarded in the UPF.

If PCC is used and if the "DDN Failure event subscription with Traffic Descriptor" PCRT is set as defined in clause 6.1.3.5 of TS 23.503 [20], the SMF interacts with the PCF and forwards the traffic descriptor before contacting the UPF; the PCF then updates an existing PCC rule or provides a new PCC rule taking into consideration the traffic descriptor for the subscribed DDN failure event.

NOTE 1: If a new PCC rule is provided by the PCF for the DDN failure event detection, the PCF populates the PCC rules as defined in clause 6.1.3.5 of TS 23.503 [20].

In the case of PDU Session with I-SMF or home-routed PDU Session, the AMF subscribes the DDN failure event towards the I/V-SMF. In the case of home-routed PDU Session, the V-SMF generates the N4 information (activating the notifications) for the V-UPF based on local configuration.

In the case of PDU Session with I-SMF, the I-SMF may request N4 information (activating the notifications) from the SMF based on local configuration and provides the Traffic Descriptor to the SMF. The SMF provides updated N4 information (activating the notifications) to the I-SMF which in turn updates the I-UPF.

For home-routed PDU Session or PDU Session with I-SMF, steps 3-4 below are performed by V-SMF/V-UPF or I-SMF/I-UPF.

3-4. When the first downlink packet matching the traffic descriptor is received in the UPF, if in step 2 the SMF indicated drop notification to the UPF, the UPF notifies the SMF and the SMF reports the DDN Failure status with NEF Correlation ID, by means of Nsmf_PDUSession_SMContextStatusNotify message, to the AMF indicated as notification endpoint.

When the first downlink packet matching the traffic descriptor is received in the UPF, if in step 2 the SMF indicated buffer notification to the UPF, the UPF notifies the SMF and the SMF may initiate Network Triggered Service Request as specified in clause 4.2.3.3. If the AMF responds Namf_Communication_N1N2MessageTransfer response with failure (e.g. due to UE not reachable, or paging no response), in addition to what is specified in clause 4.2.3.3, the SMF reports DDN Failure status with NEF Correlation ID, by means of Nsmf_PDUSession_SMContextStatusNotify message, to the AMF indicated as notification endpoint.

When the AMF receives DDN Failure status from the SMF, the AMF shall set a Notify-on-available-after-DDN-failure flag corresponding to the Notification Correlation Id and the identifier of the UE if available.

5-6. [Conditional] The AMF detects the UE is reachable and sends the event report(s) based on the Notify-on-available-after-DDN-failure flag, by means of Namf_EventExposure_Notify message(s), only to the NEF(s) indicated as notification endpoint(s) identified via the corresponding subscription in step 1. In this way, only the AF(s) for which DL traffic transmission failed are notified.

If the AMF received Idle Status Indication request in step 1 and the AMF supports Idle Status Indication, the AMF includes also the Idle Status Indication in Namf_EventExposure_Notify message.

7. The NEF sends Nnef_EventExposure_Notify message with the "Availability after DDN Failure" event to AF.

4.15.3.2.10 Number of UEs and PDU Sessions per network slice notification procedure

This procedure depicts the case of an AF subscribing to receive the registered number of UEs, or the number of PDU sessions in a specific S-NSSAI. The procedure handles the case when there is a single NSACF in the PLMN responsible for the S-NSSAI (single Service Area) or when there are multiple NSACFs responsible for the S-NSSAI in the PLMN (multiple Service Areas).

Figure 4.15.3.2.10-1: Number of UEs and PDU Sessions per network slice notification procedure

1. To subscribe or unsubscribe for the number of UEs or the number of PDU Sessions per network slice notification with the NEF, the AF sends Nnef_EventExposure Subscribe/Unsubscribe Request (Event ID, Event Filter, Event Reporting information, S-NSSAI) message to the NEF. The Event ID parameter defines the subscribed event ID, i.e. Number of Registered UEs or Number of Established PDU Sessions. The Event Filter parameter defines the S-NSSAI, in case of a trusted AF or AF-Service-Identifier as defined in TS 29.522 for an untrusted AF, for which reporting is required. The Event Reporting information parameter defines the mode of reporting, which includes threshold reporting with a threshold value or periodic reporting with included periodicity time interval. The S-NSSAI is the slice for which the subscription is requested

The AF may request one-time reporting or immediate reporting.

NOTE 1: When immediate reporting but not for one-time reporting is requested, the subscription is maintained after returning the report to the AF. When one-time reporting is requested, the subscription is terminated right after returning the report to the AF.

Notifications related to the threshold based subscriptions behave as follows:

– A single notification is sent only when the number of registered UEs or the number of established PDU Sessions reaches the threshold. A single notification is sent every time there is a change from being below the threshold to reach the threshold.

– A single notification is sent only once when the number of registered UEs or the number of established PDU Sessions go below the threshold after reaching it. A single notification is sent every time there is a change from reaching the threshold to coming down below the threshold.

2. The NEF confirms with Nnef_EventExposure_Subscribe/Unsubscribe Response message to the AF. This message may include the event reporting, if available in the NEF and immediate reporting or one-time reporting was requested by the AF. In the case of Untrusted AF, the NEF includes the AF-Service-Identifier corresponding to the S-NSSAI in the returned notification.

If immediate reporting or one-time reporting is requested, step 2 occurs after step 5 and the subscription response contains the immediate or one-time report. For the case of one-time reporting, no subscription is created at the NEF/NSACF.

3. The NEF may query the NRF to find the NSACF(s) responsible for the requested S-NSSAI. If needed, the NEF translates the AF-Service-Identifier to the corresponding S-NSSAI prior to performing the query.

4. If the NEF has not already subscribed to the event from the NSACF for the requested S-NSSAI, the NEF initiates the request Nnsacf_SliceEventExposure_Subscribe/Unsubscribe Request (Event ID, Event Filter, Event Reporting information, immediate reporting, S-NSSAI) to all the NSACFs supporting the requested S-NSSAI. The NEF stores the AF requested Event Reporting Information. If multiple NSACFs are selected for the requested S-NSSAI, the NEF may set the Event Reporting Information to periodic in its request to the NSACFs. If single NSACF is selected, the NEF sets the Event Reporting Information identical to the received request from the AF. The NEF also sets the Event ID and Event Filter identical to the received request from the AF

NOTE 2: The period chosen is selected by the NEF based on its internal logic.

5. The NSACF(s) confirms with Nnsacf_SliceEventExposure_Subscribe/Unsubscribe Response message to the NEF. This message may include the event reporting if available at NSACF and immediate reporting or one-time reporting was requested by the NEF.

6. When the reporting condition for a subscribed event is fulfilled, the NSACF triggers a notification towards the NEF.

7. The NSACF sends the Nnsacf_SliceEvent Exposure_Notify (Event ID, Event Reporting information) message to the NEF. If the subscription is for event based notification (e.g. based on the monitored event reaching a threshold value), the Event Reporting information parameter contains confirmation for the event fulfilment. If the subscription is for periodic notification or for immediate reporting, the Event Reporting information parameter provides information for the current number of UEs registered with a network slice (e.g. represented in percentage of the maximum number of the UEs registered with the network slice) or information for the current number of PDU Sessions on a network slice (e.g. represented in percentage of the maximum number of the UEs established on the network slice).

8. When a single NSACF is returned from the discovery procedure, the NEF sends the Nnef_EventExposure_Notify (Event ID, Event Reporting information) message since the reporting condition is fulfilled. In the case of Untrusted AF, the NEF includes the AF-Service-Identifier corresponding to the S-NSSAI in the returned notification.

9. When multiple NSACFs are selected for the requested NSSAI the NEF performs the aggregation from reporting NSACF(s) and maintain the overall usage of the S-NSSAI for the selected NSACFs as long as the subscription is active.

NOTE 3: If multiple NSACFs are selected for the requested S-NSSAI, the NEF continuously updates the aggregated information to be able to fulfil the incoming subscription request from the AF.

10. When multiple NSACFs are selected for the requested S-NSSAI and when the reporting condition for a subscribed event by the AF is fulfilled, the NEF sends Nnef_EventExposure_Notify (Event ID, Event Reporting information) message towards the AF. In case of untrusted AF; the NEF includes the AF-Service-Identifier corresponding to the S-NSSAI in the returned notification.

4.15.3.2.11 Network-initiated explicit event notification subscription cancel procedure

The procedure is used by the UDM to delete an event notification subscription (see clause 4.15.1).

Figure 4.15.3.2.11-1: Network-initiated event subscription removal procedure

0. An event notification subscription procedure according to clause 4.15.3.2.2 or clause 4.15.3.2.2 has already executed successfully.

1-1a. If UE subscription is withdrawn in UDM, UE authorisation to the subscribed monitoring event or UE is removed from the subscribed target group, the UDM triggers Nudm_EventExposure_Notify towards the associated notification endpoint indicating the removal of the event notification along with the time stamp. The NEF may store the information in the UDR along with the time stamp using either Nudr_DM_Create or Nudr_DM_Update service operation as appropriate.

In order to remove certain UEs in a group of UEs for which there is an event notification subscription, the UDM provides impacted UE information (e.g. SUPI, MSISDN or External Identity) to the NEF and indicates the removal of the event notification subscription for these UE(s).

2a-2b. If UE subscription information changes (e.g. UE group information changes), the UDM sends Nudm_SDM_Notification request to related serving AMF(s) to update event notification subscription information. If the UE was a group member of a previous accepted group-based event notification subscription, the AMF shall stop the event notifications for the impacted UEs. If Maximum number of Reports is applied, the AMF shall set the number of reports of the indicated UE(s) to Maximum Number of Reports.

If UE subscription data is withdrawn, the UDM sends Nudm_UECM_DeregistrationNotification request to related serving AMF(s) to remove UE subscription information. If the UE was a group member of a previous accepted group-based event notification subscription, the AMF shall keep the accepted group-based event notification subscription unless all UEs subscriptions in the group are withdrawn.

3. The NEF sends Nnef_EventExposure_Nofity to the AF reporting event received by Nudm_EventExposure_Notify.

If the NEF receives UE Identifier(s) in step 1 for a group-based event notification subscription and the Maximum Number of Reports applies to the group-based event notification subscription, the NEF sets the number of reports of the indicated UE(s) to Maximum Number of Reports. The NEF sends Nnef_EventExposure_Notify to the AF and includes MSISDN(s) or External Identifier(s). If NEF determines that the reporting for the group is complete based on the update above, the NEF deletes the associated event notification subscription and requests that the UDM deletes the related event notification subscription for the group.

4.15.3.2.12 Void

4.15.3.2.13 Handling AF requests when the UE is identified via UE addressing information

An AF may request, via the NEF, the Event Exposure (as defined in clause 4.15.3) or the parameter provisioning (as defined in clause 4.15.6) targeting an individual UE, identifying the target UE by providing UE addressing information.

In this case the 5GC first needs to retrieve a UE Identifier based on:

– the UE addressing information as provided by the AF: this may correspond to an UE IP address as allocated by 5GC or to a MAC address of the UE (when Ethernet PDU Sessions are targeted),

– the corresponding DNN and/or S-NSSAI: this may have been provided by the AF or, alternatively, determined by the NEF using the identity of the AF.

The NEF retrieves the UE Identifier by executing step 2 to 6 of the AF specific UE Identifier retrieval procedure described in clause 4.15.10.

Once this is done, the 5GC may carry out the action requested by the AF and may deliver back to the AF an External Identifier representing an AF specific UE Identifier (as defined in TS 23.501 [2]). This AF specific UE Identifier may later be used by the AF to issue further requests about the same UE.

NOTE: The AF can use UE addressing information to identify the UE in a subscription request, but once received, this UE addressing information is translated into a GPSI and then the 5GC considers the subscription is associated with the GPSI and not with the UE address any more.

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 the returned AF specific UE Identifier and the UE IP address as this mapping may change.