6.4 Network Exposure to Edge Application Server

23.5483GPP5G System Enhancements for Edge ComputingRelease 17Stage 2TS

6.4.1 General

Some real time network information, e.g. user path latency, are useful for application layer. In this release, in order to expose network information timely to local AF, the L-PSA UPF may expose i.e. QoS monitoring results as defined in clause 5.33.3 of TS 23.501 [2], to the local AF.

NOTE 1: Local PSA UPF can expose the QoS monitoring results to local AF via N6. How to deliver the information on N6 is out of the scope of the present document.

NOTE 2: Sending QoS monitoring information that has not been properly integrated over time, i.e. with over-high frequency, can increase risk that the application may over-react to instantaneous radio events/conditions e.g. leading to service instability.

6.4.2 Network Exposure to Edge Application Server

6.4.2.1 Usage of Nupf_EventExposure to Report QoS Monitoring results

The UPF may be instructed to report information about a PDU Session directly i.e. bypassing the SMF and the PCF. This reporting may target an Edge Application Server (EAS) or a local AF that itself interfaces the EAS.

Local NEF deployed at the edge may be used to support network exposure with low latency to local AF. The local NEF may support one or more of the functionalities described in clause 6.2.5.0 of TS 23.501 [2]. and may support a subset of the APIs specified for capability exposure based on local policy. In order to support the network exposure locally, the local NEF shall support Nnef_AFSessionWithQoS service operation for the local AF. The local NEF selection by AF is described in clauses 6.2.5.0 and 6.3.14 of TS 23.501 [2].

The local AF subscribes the direct notification of QoS Monitoring results from the PCF via a local NEF or NEF. If the NEF detects that it is not the most suitable NEF instance to serve the local AF request, it may redirect the AF to a local NEF instance.

NOTE 1: If the notifications need to go via the local NEF, then the local NEF needs to be involved in order to be able to map these notifications to the URI where the AF expects to receive them.

The local AF may also use the Npcf_PolicyAuthorization_Create or Update service of the PCF directly. In this case, reporting is done directly from the UPF to the local AF.

Based on the indication of direct event notification and operator’s policy, the PCF includes Direct event notification method and the Target of reporting (including target local NEF address or target AF address) within the PCC rule that it provides to the SMF as described in clause 6.1.3.21 of TS 23.503 [4].

The SMF sends the QoS monitoring request to the RAN and N4 rules to the L-PSA UPF. If the L-PSA UPF supports such reporting, N4 rules indicate that the QoS flow needs direct notification of QoS Monitoring. When QoS monitoring of GTP-U Path(s) is used, it is also activated if needed. This is as defined in clause 5.33.3 of TS 23.501 [2]. When N4 rules indicate that the QoS flow needs direct notification of QoS Monitoring results, upon the detection of the QoS monitoring event (e.g. when threshold for the packet delay of the QoS flow is reached as defined in clause 5.33.3 of TS 23.501 [2]), the L-PSA UPF notifies the QoS Monitoring event information to the AF (directly or via Local NEF). If the L-PSA UPF supports the Nupf_EventExposure_Notify service operation, as defined in clause 5.2.26 of TS 23.502 [3], the L-PSA UPF sends the Nupf_EventExposure_Notify to the Notification Target Address indicated by the Session Reporting Rule received from the SMF. The Notification Target Address may correspond to the AF or to a local NEF. When the Notification Target Address corresponds to a Local NEF, the local NEF reports the QoS Monitoring result to the AF.

During UE mobility, the SMF may trigger the L-PSA UPF relocation/reselection and then send the N4 rules to the new L-PSA UPF to indicate the QoS flow needs direct notification of QoS Monitoring. The UE mobility may also trigger AF relocation or local NEF reselection, then the local AF should update the subscription for local exposure with QoS monitoring results possibly via local NEF, towards the PCF. This updated /new subscription is then propagated via SMF (via PCC rule updates) and then to the L-PSA UPF via N4 rules.

NOTE 2: The new local AF can subscribe direct notification of QoS Monitoring if Edge Relocation Involving AF Change happens as described in clause 6.3.2.

Figure 6.4.2.1-1: Network exposure to Edge Application Server

0. The UE establishes a PDU Session as defined in clause 4.3.2.2.1 of TS 23.502 [3] A L-PSA UPF is assigned for this PDU Session.

1. The AF initiates setting up an AF session with required QoS procedure as defined in clause 4.15.6.6 of TS 23.502 [3].

In the request, the AF may subscribe to direct notification of QoS monitoring results for the service data flow to PCF possibly via Local NEF or NEF. If so, the AF shall include the corresponding QoS monitoring parameters as defined in clause 6.1.3.21 of TS 23.503 [4] and in TS 23.502 [3].

The AF may also first initiate an AF Session with PCF and later subscribe to direct notification of QoS monitoring to PCF by invoking Npcf_PolicyAuthorization_Update service operation.

The local AF or NEF may discover a local NEF as specified in clause 6.2.5.0 of TS 23.501 [2] and using parameters as specified in clause 6.3.14. Alternatively, if the NEF detects that it is not the most suitable NEF instance to serve the local AF request, the NEF may redirect the AF to a (more) local NEF. The NEF may use information on the L-PSA UPF for this determination.

2. The PCF makes the policy decision and initiates the PDU Session modification procedure as defined in clause 4.3.3.2 of TS 23.502 [3], steps 1b, 3b, 4-8b.

If the direct notification of QoS monitoring results is subscribed, the PCF includes the Direct event notification method and the Target of reporting (including target local NEF or local AF address) in the PCC rule of the service data flow as described in clause 6.1.3.21 of TS 23.503 [4].

If the SMF receives the Direct event notification form the PCF and the SMF determines that the L-PSA UPF supports such reporting, the SMF determines the QoS monitoring parameters based on the information received from the PCF and/or local configuration and provides them to the L-PSA UPF via N4 rules as described in clause 5.33.3.1 of TS 23.501 [2]. Otherwise the SMF activates N4 reporting for the QoS monitoring results. The PCF may determine that the duplicated notification is required, i.e. both, direct notification to the AF (i.e. sent from UPF) and notification sent to the PCF/SMF is required and indicate it to the SMF using the Direct event notification method in the PCC rule as described in clause 6.1.3.21 of TS 23.503 [4]. In this case, the SMF shall activate the N4 reporting together with the direct reporting to the local NEF/AF.

NOTE 2: The details of the parameters for the control of the QoS monitoring as well as the PCF and SMF behaviour are described in clause 6.1.3.21 of TS 23.503 [4] and in clause 5.33.3.1 of TS 23.501 [2], respectively.

3. The L-PSA UPF obtains QoS monitoring information as defined in clause 5.33.3 of TS 23.501 [2].

4. The L-PSA UPF sends the notification related with QoS monitoring information over Nupf_EventExposure_Notify service operation. The notification is sent to Notification Target Address that may correspond (4a) to the local AF or (4b) to the local NEF.

5. If Local NEF is used, it reports the real-time network information to local AF by invoking Nnef_EventExposure_Notify service operation.

6. Due to e.g. UE mobility, the PSA relocation and/or EAS relocation may happen as described in clause 6.3. During the PSA and/or EAS relocation (if the event was subscribed e.g. as in step 1), the SMF notifies the (local) NEF or the AF with the PSA and/or EAS relocation, and the AF may trigger a new L-NEF discovery as in step 1. During this step, the application mechanisms may involve a new AF for this session.

7. The new AF may initiate a new AF session to (re-)subscribe the direct notification of QoS monitoring as described in steps 1-4.

8. The old AF revokes the AF session.

NOTE 3: Step 8 can take place before step 7.

6.4.2.2 Local NEF Discovery

As specified in clause 6.2.5.0 of TS 23.501 [2], the NRF may be used by the AF to discover the L-NEF. To become discoverable, the L-NEF registers with an NRF deployed within the operator’s domain where the AF resides.

The AF uses existing procedures as described in clause 4.17.4 of TS 23.502 [3] to discover the L-NEF. If the AF only knows the NEF and it initiates a Nnef_AFSessionWithQoS_Create/Update_request procedure with an indication of direct event notification as described in clause 6.4.2.1 and clause 6.1.3.21 of TS 23.503 [4], the NEF may decide that it is not suitable for local exposure, and re-direct the request to an L-NEF as described in TS 29.500 [9]. NEF may use NRF to find a suitable L-NEF for the re-direction.