Content for  TS 23.502  Word version:  18.5.0

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 TS 23.501. The SMF decides to apply this behaviour based on the "expected UE behaviour". Alternatively, step 0 is triggered by step 3,

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.

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.

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.

The SMF sends the Nsmf_EventExposure_Subscribe Response message to the UDM.

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

The NEF sends the Nsmf_EventExposure_Subscribe response to the AF.

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.

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

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

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 TS 23.501. The SMF decides to apply this behaviour based on the "expected UE behaviour". Alternatively, step 0 is triggered by step 5.

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.

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.

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.

The AMF acknowledges the execution of Namf_EventExposure_Subscribe.

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).

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

The UDM sends the Nudm_EventExposure_Subscribe response to the NEF.

The NEF sends the Nsmf_EventExposure_Subscribe response to the AF.

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.

[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.

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

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.

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, 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. 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.

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.

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

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

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.

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, 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. 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.

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.

[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.

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

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

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).

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.

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.