Section: 4.3.6 Application Function influence on traffic routing and service function chaining 4.3.6.1 General
Content: Clause 4.3.6 describes the procedures between an Application Function and the SMF to maintain an efficient user plane path and/or to provide N6-LAN service function chaining for Application Functions that require it. As described in clauses 5.6.7 and 5.6.16 of TS 23.501[ System architecture for the 5G System (5GS) ]  [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 and/or influence the steering of user traffic to service function chain(s) identified by SFC identifier(s). The AF may also provide in its request subscriptions to SMF events. The following cases can be distinguished: NOTE 1: Such requests target an on-going PDU Session. When receiving an AF request on Application Function influence on traffic routing targeting an individual UE IP address the NEF needs to determine whether the target PDU Session is working in HR-SBO mode. If the target PDU Session is NOT working in HR-SBO mode (non roaming or LBO PDU Session) then the NEF contacts the PCF of the PDU Session as further defined in the clause 4.3.6.4; If the target PDU Session is working in HR-SBO mode, the NEF does not contact the PCF of the PDU session but needs to store the AF request in UDR as defined in clause 4.3.6.5. The NEF determines whether the PDU Session that the AF requests to influence is working in HR-SBO mode or not and in the former case determines the HPLMN of the UE, the DNN/S-NSSAI of the PDU Session as follows: If the AF has not provided the (H)PLMN ID, DNN, S-NSSAI: - If the IP address of the UE in the AF request is a private IP address, the NEF determines the HPLMN of the UE, the DNN/S-NSSAI of the PDU Session based on local configuration. - If the IP address of the UE in the AF request is a public IP address: - if this Public address belongs to a range NOT owned by the PLMN of the NEF, then the target PDU Session is working in HR-SBO mode and the NEF determines the HPLMN of UE, the DNN/S-NSSAI of the PDU Session based on that range. The NEF (that has received the AF request) contacts the NEF of the HPLMN in order to retrieve the UE IP address of the PDU Session from the PSA UPF in the HPLMN. - Otherwise, if the UE IP Address in the AF request is an IP address NATed by the PLMN that the NEF belongs to, the NEF invokes steps 3 to 6 of the AF specific UE ID retrieval procedure defined in clause 4.15.10 to get the corresponding private UE IP address, an indication that the PDU Session is working in HR-SBO mode, the HPLMN of UE, the DNN/S-NSSAI of the PDU Session from the L-PSA UPF in the local PLMN. NOTE 2: In this Release, the HPLMN allows HR-SBO for a PDU session only if the UE IP address of the PDU Session has not been allocated in a range that may overlap with other PDU sessions to the same DNN and S-NSSAI of that HPLMN. NOTE 3: It is assumed that the NEF is configured with the NATed IP range of its own PLMN. It is assumed that the NEF is configured based on HR-SBO roaming agreements for the DNN/S-NSSAI with the association of Public IP address ranges with an HPLMN ID, a DNN/S-NSSAI. NOTE 4: Whether the AF needs to use the NEF or not is according to local deployment. If the AF request is expected to possibly address PDU Sessions in HR-SBO mode, then the AF sends its requests via the NEF. When AF requests are routed (by the AF or by the NEF) to an individual PCF this may use the BSF. This case applies to both AF influence on traffic routing as well as AF influence on Service Function Chaining. This is described in clause 4.3.6.4. - AF requests described in clause 5.6.7 of TS 23.501[ System architecture for the 5G System (5GS) ]  [2] or clause 5.6.16 of TS 23.501[ System architecture for the 5G System (5GS) ]  [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) or targeting UEs with External Subscriber Category(s) which can be combined with External Group ID(s) or any UE 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[ System architecture for the 5G System (5GS) ]  [2] and further described in clause 4.3.6.2. NOTE 5: Such requests can target on-going or future PDU Sessions. If the AF request targets any UE the procedure described in clause 4.3.6.5 may also be performed. In that case if the HPLMN Id, DNN and S-NSSAI has not been provided by the AF, the NEF determines the target HPLMN Id, DNN and S-NSSAI based on local configuration, This version of the specification does not support the procedure described in clause 4.3.6.5 if the AF request targets an external group of UE(s), or UE(s) identified by SUPI. If the AF request targets a GPSI, the NEF determines the GPSI owner PLMN Id from the GPSI and invokes the NEF of that PLMN that retrieves the SUPI from HPLMN. In that case if the DNN and/or S-NSSAI has not been provided by the AF a preconfigured DNN and/or S-NSSAI is used. If the AF interacts with 5GC via the NEF, the NEF performs the following mappings or determinations 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 External Subscriber Category(s) and any UE, or External Subscriber Category and External Group ID(s) to, Internal Group ID(s) or Internal Group ID(s) and Subscriber Category(s). - Map the geographical area in Spatial Validity Condition into areas of validity, determined by local configuration. - Determine whether an AF request targeting an UE IP address corresponds to HR-SBO and if yes determine as defined above the HPLMN of UE, the DNN/S-NSSAI of the PDU Session based on the AF request, the received UE IP address and its local configuration, NOTE 6: As a user can be associated with multiple Subscriber Category(s), some values of Subscriber Category(s) can correspond to an SLA between an application provider represented by an AF and the 5GC operator. In the NEF API, the combination of application identifier and External Subscriber Category can also be used to refer to this SLA.