4.3.6 Application Function influence on traffic routing

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

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

4.3.6.1 General

Clause 4.3.6 describes the procedures between an Application Function and the SMF to maintain an efficient user plane path for Application Functions that require it.

As described in clause 5.6.7 of TS 23.501 [2], an Application Function may send requests to influence SMF routeing decisions for User Plane traffic of PDU Sessions. The AF requests may influence UPF (re)selection and allow routeing of user traffic to a local access (identified by a DNAI) to a Data Network. The AF may also provide in its request subscriptions to SMF events.

The following cases can be distinguished:

– AF requests targeting an individual UE by a UE address; these requests are routed (by the AF or by the NEF) to an individual PCF using the BSF. This is described in clause 4.3.6.4.

NOTE 1: Such requests target an on-going PDU Session. Whether the AF needs to use the NEF or not is according to local deployment.

– AF requests described in clause 5.6.7 of TS 23.501 [2] targeting a group of UE(s), or any UE accessing a combination of DNN and S-NSSAI, or targeting individual UE(s) by one or more GPSI(s) as described in table 5.6.7-1. These AF requests may also affect UE(s) with an established PDU session. For such requests the AF shall contact the NEF and the NEF stores the AF request information in the UDR. PCF(s) receive a corresponding notification if they had subscribed to the creation / modification/ deletion of the AF request information corresponding to UDR Data Keys / Data Sub-Keys. This is defined in clause 6.3.7.2 of TS 23.501 [2] and further described in clause 4.3.6.2.

NOTE 2: Such requests can target on-going or future PDU Sessions.

If the AF interacts with PCF via the NEF, the NEF performs the following mappings where needed:

– Map the AF-Service-Identifier into DNN and S-NSSAI combination, determined by local configuration.

– Map the AF-Service-Identifier into a list of DNAI(s) and Routing Profile ID(s) determined by local configuration.

The NEF can only provide this mapping when the DNAI(s) being used by the applications are statically defined. When the DNAI(s) where applications are instantiated may vary dynamically, the AF should provide the target DNAI(s) in its request together with either Routing Profile ID(s) or with N6 traffic routing information.

– Map the GPSI in Target UE Identifier into SUPI, according to information received from UDM.

– Map the External Group Identifier in Target UE Identifier into Internal Group Identifier, according to information received from UDM.

– Map the geographical area in Spatial Validity Condition into areas of validity, determined by local configuration.

4.3.6.2 Processing AF requests to influence traffic routing for Sessions not identified by an UE address

Figure 4.3.6.2-1: Processing AF requests to influence traffic routing for Sessions not identified by an UE address

NOTE 1: The 5GC functions used in this scenario are assumed to all belong to the same PLMN (HPLMN in non-roaming case or VPLMN in the case of a PDU Session in LBO mode).

NOTE 2: Nnef_TrafficInfluence_Create or Nnef_TrafficInfluence_Update or Nnef_TrafficInfluence_Delete service operations invoked from an AF located in the HPLMN for local breakout and home routed roaming scenarios are not supported.

1. To create a new request, the AF invokes a Nnef_TrafficInfluence_Create service operation. The content of this service operation (AF request) is defined in clause 5.2.6.7. The request contains also an AF Transaction Id. If it subscribes to events related with PDU Sessions the AF indicates also where it desires to receive the corresponding notifications (AF notification reporting information).

To update or remove an existing request, the AF invokes a Nnef_TrafficInfluence_Update or Nnef_TrafficInfluence_Delete service operation providing the corresponding AF Transaction Id.

The Nnef_TrafficInfluence_Create (initiated by target AF) or Nnef_TrafficInfluence_Update (initiated by source AF or target AF) service operation may be used for the case of AF instance change. If Nnef_TrafficInfluence_Update service operation is invoked, the NEF is required to update the subscription resource. The Nnef_TrafficInfluence_Update service operation may include an updated notification target address. The updated subscription resource is used by the target AF.

NOTE 3: If the source AF transfers the application context to the target AF, then target AF may create new subscription via Nnef_TrafficInfluence_Create operation or update existing subscription via Nnef_TrafficInfluence_Update. However, whether and how the application context transfer is done is out of this specification.

2. The AF sends its request to the NEF. If the request is sent directly from the AF to the PCF, the AF reaches the PCF selected for the existing PDU Session by configuration or by invoking Nbsf_management_Discovery service.

The NEF ensures the necessary authorization control, including throttling of AF requests and, as described in clause 4.3.6.1, mapping from the information provided by the AF into information needed by the 5GC.

3. (in the case of Nnef_TrafficInfluence_Create or Update): The NEF stores the AF request information in the UDR (Data Set = Application Data; Data Subset = AF traffic influence request information, Data Key = AF Transaction Internal ID, S-NSSAI and DNN and/or Internal Group Identifier or SUPI).

NOTE 4: Both the AF Transaction Internal ID and, S-NSSAI and DNN and/or Internal Group Identifier or SUPI are regarded as Data Key when the AF request information are stored into the UDR, see Table 5.2.12.2.1-1.

(in the case of Nnef_TrafficInfluence_delete): The NEF deletes the AF requirements in the UDR (Data Set = Application Data; Data Subset = AF traffic influence request information, Data Key = AF Transaction Internal ID).

The NEF responds to the AF.

4. The PCF(s) that have subscribed to modifications of AF requests (Data Set = Application Data; Data Subset = AF traffic influence request information, Data Key = S-NSSAI and DNN and/or Internal Group Identifier or SUPI) receive(s) a Nudr_DM_Notify notification of data change from the UDR.

5. The PCF determines if existing PDU Sessions are potentially impacted by the AF request. For each of these PDU Sessions, the PCF updates the SMF with corresponding new policy information about the PDU Session by invoking Npcf_SMPolicyControl_UpdateNotify service operation as described in steps 5 and 6 in clause 4.16.5.

If the AF request includes a notification reporting request for UP path change, the PCF includes in the PCC rule(s) the information required for reporting the event, including the Notification Target Address pointing to the NEF or AF and the Notification Correlation ID containing the AF Transaction Internal ID.

If the AF request includes an EAS Correlation indication or indication of traffic correlation, PCF includes in the PCC rule(s) an EAS Correlation indication or indication of traffic correlation, and a Traffic Correlation ID corresponding to a set of UEs that AF request aims at.

Editor’s note: How Traffic Correlation ID is designed is FFS.

The PCF may, optionally, use service experience analytics per UP path, as defined in clause 6.4.3 of TS 23.288 [50], to provide an updated list of DNAI(s) to the SMF.

6. When the updated policy information about the PDU Session is received from the PCF, the SMF may take appropriate actions to reconfigure the User plane of the PDU Session. The SMF may consider service experience analytics and/or DN Performance analytics per UP path (i.e. including UPF and/or DNAI and/or AS instance) as defined in clauses 6.4.3 and 6.14.3, respectively, of TS 23.288 [50] before taking such actions. Examples of actions are:

– Determining a target DNAI and adding, replacing or removing a UPF in the data path to e.g. act as an UL CL or a Branching Point e.g. as described in clause 4.3.5.

– Allocate a new Prefix to the UE (when IPv6 multi-Homing applies).

– Updating the UPF in the target DNAI/Common DNAI with new traffic steering rules.

– Subscribe to notifications from the AMF for an Area of Interest via Namf_EventExposure_Subscribe service operation.

– Determining whether to relocate PSA UPF considering the user plane latency requirements provided by the AF (see clause 6.3.6 of TS 23.548 [74]).

When the updated policy information about the PDU Session is received from the PCF, the SMF may take appropriate actions to assist the EAS discovery and re-discovery for PDU Session with Session Breakout connectivity model such as:

– Retrieve the EAS deployment information as defined in clause 6.2.3.4.1 of TS 23.548 [74].

– Providing DNS message handling rule to forward DNS messages of the UE and/or report when detecting DNS messages as defined in clause 6.2.3.2.2 of TS 23.548 [74].

7. The SMF may decide whether it is required to send the target DNAI to the AMF for triggering SMF/I-SMF (re)selection and then inform the target DNAI information for the current PDU session or for the next PDU session to AMF via Nsmf_PDUSession_SMContextStatusNotify service operation.

4.3.6.3 Notification of User Plane Management Events

The SMF may send a notification to the AF if the AF had subscribed to user plane management event notifications as described in clause 4.3.6.2 and in clause 5.6.7 of TS 23.501 [2]. The following are the examples of such events:

– A PDU Session Anchor identified in the AF subscription request has been established or released.

– A DNAI has changed.

– The SMF has received a request for AF notification and the on-going PDU Session meets the conditions to notify the AF.

– Ethernet PDU Session Anchor Relocation as defined in clause 4.3.5.8.

The SMF uses notification reporting information received from PCF to issue the notification either via an NEF (2a, 2b and 4a, 4b) or directly to the AF (2c and 4c).

The following flow depicts the sequence of events:

Figure 4.3.6.3-1: Notification of user plane management event

1. A condition for an AF notification has been met as described above. The SMF sends notification to the NF that is subscribed for SMF notifications. Further processing of the SMF notification depends on the receiving NF, as shown in steps 2a and 2c.

2a. If early notification via NEF is requested by the AF, the SMF notifies the NEF of the target DNAI of the PDU Session and may indicate capability of supporting EAS IP replacement in 5GC by invoking Nsmf_EventExposure_Notify service operation.

2b. When the NEF receives Nsmf_EventExposure_Notify, the NEF performs information mapping (e.g. AF Transaction Internal ID provided in Notification Correlation ID to AF Transaction ID, SUPI to GPSI, etc.) as applicable according to clause 5.6.7 of TS 23.501 [2] and triggers the appropriate Nnef_TrafficInfluence_Notify message. In this case, step 2c is not applicable.

2c. If early direct notification is requested by the AF, the SMF notifies the AF of the target DNAI of the PDU Session and may indicate capability of supporting EAS IP replacement in 5GC by invoking Nsmf_EventExposure_Notify service operation.

2d. The AF replies to Nnef_TrafficInfluence_Notify by invoking Nnef_TrafficInfluence_AppRelocationInfo service operation either immediately or after any required application relocation in the target DNAI is completed. The AF may include N6 traffic routing details corresponding to the target DNAI and /or the ‘uplink buffering’ indication to indicate that buffering of uplink traffic to the target DNAI is needed. The AF may include Information for EAS IP Replacement in 5GC. AF may reply in negative e.g. if the AF determines that the application relocation cannot be completed successfully and/or on time.

NOTE 1: The maximum time the new PSA is to buffer UL data relates to the maximum delay between steps 4a-4c and step 4f/4g of Figure 4.3.6.3-1. SMF local policies can control this maximum time.

NOTE 2: The traffic being buffered is the traffic associated with the PCC rule that has requested the notification.

2d-a. If information sent via Nnef_TrafficInfluence_Create is to be changed e.g. N6 traffic routing details corresponding to the target DNAI, the AF invokes Nnef_TrafficInfluence_update service operation in order for PCF to be able to include this information in PCC rules sent to SMF.

If the AF includes information such as N6 traffic routing details corresponding to the target DNAI in Nnef_TrafficInfluence_AppRelocationInfo it shall include the same information in Nnef_TrafficInfluence_update.

2e. When the NEF receives Nnef_TrafficInfluence_AppRelocationInfo, the NEF triggers the appropriate Nsmf_EventExposure_AppRelocationInfo message.

2e-a. When the NEF receives Nnef_TrafficInfluence_update, the NEF triggers step 3a as in Figure 4.3.6.2-1 or step 2 of Figure 4.3.6.4-1 if targeting an individual UE by a UE address.

2f. The AF replies to Nsmf_EventExposure_Notify by invoking Nsmf_EventExposure_AppRelocationInfo service operation either immediately or after any required application relocation in the target DNAI is completed. The AF may include N6 traffic routing details corresponding to the target DNAI and /or the ‘uplink buffering’ indication to indicate that buffering of uplink traffic to the target DNAI is needed. The AF may include Information for EAS IP Replacement in 5GC. AF may reply in negative e.g. if the AF determines that the application relocation cannot be completed successfully on time.

2f-a. If information sent via Npcf_PolicyAuthorization_Create is to be changed e.g. N6 traffic routing details corresponding to the target DNAI, the AF invokes Npcf_PolicyAuthorization_Update service operation in order for PCF to be able to include this information in PCC rules sent to SMF.

If the AF includes information such as N6 traffic routing details corresponding to the target DNAI in Nsmf_EventExposure_AppRelocationInfo it shall include the same information in Npcf_PolicyAuthorization_Update.

3. The SMF enforces the change of DNAI or addition, change, or removal of a UPF. This may correspond to the mechanisms described in Figure 4.3.5.6-1 or in Figure 4.3.5.7-1.

If the runtime coordination between 5GC and AF is enabled based on local configuration, according to the indication of "AF acknowledgment to be expected" included in AF subscription to SMF events, the SMF may wait for a response from the AF to the early notification before this step. The SMF does not perform this step until it receives a positive response from the AF, as described in clause 5.6.7 of TS 23.501 [2].

4a. If late notification via NEF is requested by the AF, the SMF notifies the NEF of the target DNAI of the PDU Session and may indicate capability of supporting EAS IP replacement in 5GC by invoking Nsmf_EventExposure_Notify service operation.

If the runtime coordination between 5GC and AF is enabled based on local configuration, according to the indication of "AF acknowledgment to be expected" included in AF subscription to SMF events, the SMF may send late notification and wait for a positive response from the AF before activating the new UP path, as described in clause 5.6.7 of TS 23.501 [2].

4b. When the NEF receives Nsmf_EventExposure_Notify, the NEF performs information mapping (e.g. AF Transaction Internal ID provided in Notification Correlation ID to AF Transaction ID, SUPI to GPSI, etc.) as applicable according to clause 5.6.7 of TS 23.501 [2] and triggers the appropriate Nnef_TrafficInfluence_Notify message. In this case, step 4c is not applicable.

4c. If late direct notification is requested by the AF, the SMF notifies the AF of the target DNAI of the PDU Session and may indicate capability of supporting EAS IP replacement in 5GC by invoking Nsmf_EventExposure_Notify service operation.

4d. When the AF receives either the Nnef_TrafficInfluence_Notify message or the Nsmf_EventExposure_Notify message, the AF checks whether it can serve the target DNAI. If the AF instance change is needed, the AF determines the proper target AF for the target DNAI and performs the AF migration.

NOTE 1: The determination of the target AF for the target DNAI and the AF migration to the target AF are out of the scope of this release.

4e. The AF replies to Nnef_TrafficInfluence_Notify by invoking Nnef_TrafficInfluence_AppRelocationInfo service operation either immediately or after any required application relocation in the target DNAI is completed. AF includes N6 traffic routing details corresponding to the target DNAI. AF may reply in negative e.g. if the AF determines that the application relocation cannot be completed successfully on time. Nnef_TrafficInfluence_AppRelocationInfo with positive response may indicate that buffering of uplink traffic to the target DNAI is no more needed.

4e-a. If information sent via Nnef_TrafficInfluence_Create/Update is to be changed e.g. N6 traffic routing details corresponding to the target DNAI, the AF invokes Nnef_TrafficInfluence_Create or Nnef_TrafficInfluence_Update service operation in order for PCF to be able to include this information in PCC rules sent to SMF. The Nnef_TrafficInfluence_Create shall be used if the AF is notified (e.g. in step 4b) that the UE IP address is changed and the initial Nnef_TrafficInfluence_Create was targeted to an individual UE address, otherwise the Nnef_TrafficInfluence_Update may be used.

4f. When the NEF receives Nnef_TrafficInfluence_AppRelocationInfo, the NEF triggers the appropriate Nsmf_EventExposure_AppRelocationInfo message.

4f-a. When the NEF receives Nnef_TrafficInfluence_Create/update, the NEF triggers step 3a as in Figure 4.3.6.2-1 or step 2 of Figure 4.3.6.4-1 if targeting an individual UE by a UE address.

4g. The AF replies to Nsmf_EventExposure_Notify by invoking Nsmf_EventExposure_AppRelocationInfo service operation either immediately or after any required application relocation in the target DNAI is completed. AF includes N6 traffic routing details corresponding to the target DNAI. AF may reply in negative e.g. if the AF determines that the application relocation cannot be completed successfully on time. Nsmf_EventExposure_AppRelocationInfo with positive response may indicate that buffering of uplink traffic to the target DNAI is no more needed.

4g-a. If information sent via Npcf_PolicyAuthorization_Create/Update is to be changed e.g. N6 traffic routing details corresponding to the target DNAI, the AF invokes Npcf_PolicyAuthorization_Create or Npcf_PolicyAuthorization_Update service operation in order for PCF to be able to include this information in PCC rules sent to SMF. The Npcf_PolicyAuthorization_Create shall be used if the AF is notified (e.g. in step 4c) that the UE IP address is changed, otherwise the Npcf_PolicyAuthorization_Update may be used.

4.3.6.4 Transferring an AF request targeting an individual UE address to the relevant PCF

Figure 4.3.6.4-1: Handling an AF request targeting an individual UE address to the relevant PCF

Depending on the AF deployment (see clause 6.2.10 of TS 23.501 [2]), the AF may send the AF request to PCF directly, in which case step 1 is skipped, or via the NEF.

1. [Conditional] If the AF sends the AF request via NEF, the AF sends Nnef_TrafficInfluenceCreate/Update/Delete Request targeting an individual UE address to the NEF. This request corresponds to an AF request to influence traffic routing that targets an individual UE address.

When NEF receives an AF request from AF, the NEF ensures the necessary authorization control and, as described in clause 4.3.6.1, mapping from the information provided by the AF into information needed by the 5GC. The NEF responds to the AF.

2. [Conditional] AF/NEF consumes Nbsf_Management_Discovery service operation (providing at least the UE address) to find out the address of the relevant PCF if the PCF address is not available on the NEF based on local configuration, otherwise step 1 is skipped.

NOTE 1: The AF/NEF finds the BSF based on local configuration or using the NRF.

3. BSF provides the PCF address in the Nbsf_Management_Discovery response to AF/NEF.

4. If step 1 was performed, NEF invokes the Npcf_PolicyAuthorization service to the PCF to transfer the AF request. If an AF sends the AF request directly to the PCF, AF invokes Npcf_PolicyAuthorization service and the PCF responds to the AF. To support the AF instance change, the Npcf_PolicyAuthorization_Create (initiated by target AF) or Npcf_PolicyAuthorization_Update (initiated by source AF or target AF) service operation may be used.

NOTE 2: If the source AF transfers the application context to the target AF, then target AF may create new subscription via Npcf_PolicyAuthorization_Create or update existing subscription via Npcf_PolicyAuthorization_Update. However, whether and how the application context transfer is done is out of this specification.

5. The PCF authorizes the AF request. If the PCF determines that the requirements can’t be authorized, it rejects the AF request. Once the PCF authorizes the AF request, the PCF updates the SMF with corresponding new PCC rule(s) with PCF initiated SM Policy Association Modification procedure as described in clause 4.16.5.2.

The PCF may, optionally, use service experience analytics per UP path, as defined in clause 6.4.3 of TS 23.288 [50], to provide a an updated list of DNAI(s) to the SMF.

If Npcf_PolicyAuthorization_Update service operation is invoked, the PCF is required to update the subscription resource. The Npcf_PolicyAuthorization_Update service operation may include an updated notification target address. The updated subscription resource is used by the target AF.

When a PCC rule is received from the PCF, the SMF may take appropriate actions, when applicable, to reconfigure the User plane of the PDU Session. The SMF may consider service experience analytics and/or DN Performance analytics per UP path (i.e. including UPF and/or DNAI and/or AS instance) as defined in clauses 6.4.3 and 6.14.3, respectively, of TS 23.288 [50] before taking such actions. Examples of actions are:

– Determining a target DNAI and adding, replacing or removing UPF(s) in the data path, e.g. to act as UL CL, Branching Point, and/or PDU Session Anchor e.g. as described in clause 4.3.5.

– Allocate a new Prefix to the UE (when IPv6 multi-Homing applies).

– Updating the UPF regarding the target DNAI with new traffic steering rules.

– Subscribe to notifications from the AMF for an Area of Interest via Namf_EventExposure_Subscribe service operation.

– Determining whether to relocate PSA UPF considering the user plane latency requirements provided by the AF (see clause 6.3.6 of TS 23.548 [74]).