3GPP 23.501 v20.2.0 — the document's own text
5.6.16.2 Application Function influence on Service Function Chaining
Taught in 12. The connection to a data network (The 5G system architecture, in depth), 5. The connection, and what is promised on it (The 5G system architecture, overview).
An AF may request the steering of user plane traffic to a pre-configured chain of Service Functions on N6-LAN.
In the non-roaming scenario, Application Function influence on Service Function Chaining and Application Function influence on traffic routing (as defined in clause 5.6.7) can be applicable to the same traffic simultaneously.
It is assumed that a service level agreement exists between the operator and a third party that includes a list of authorized predefined Service Function Chains (SFCs), each SFC being identified based on a Service Function Chaining identifier (SFC ID). The AF may request the selected traffic flows to be steered towards a specific SFC, either at PDU Session establishment or any time after PDU Session establishment.
The AF requests may be sent to the PCF via the NEF. When SFC ID is included in the AF request, the parameters listed in Table 5.6.16.2-1 may be included in the AF request.
Table 5.6.16.2-1: Information element contained in AF request
| Information Name | Applicable for PCF or NEF (NOTE 1) | Applicable for NEF only | Category |
|---|---|---|---|
| Traffic Description | Defines the target traffic to be influenced, represented by the combination of DNN and optionally S-NSSAI and application identifier or traffic filtering information. | The target traffic can be represented by AF-Service-Identifier, instead of combination of DNN and optionally S-NSSAI. | Mandatory |
| Target UE Identifier(s) | Indicates the UE(s) that the request is targeting, i.e. an individual UE, a group of UE represented by Internal Group Identifier (NOTE 2), or any UE accessing the combination of DNN and S-NSSAI. | GPSI can be applied to identify the individual UE, or External Group Identifier can be applied to identify a group of UE. | Mandatory |
| Spatial Validity Condition | Indicates that the request applies only to the traffic of UE(s) located in the specified location, represented by areas of validity. | The specified location can be represented by geographical area. | Optional |
| AF transaction identifier | The AF transaction identifier refers to the AF request. | N/A | Mandatory |
| SFC identifier(s) | Indicates the pre-defined Service Function Chain in downlink and/or uplink. | N/A | Mandatory |
| Metadata | Contains information that is transparently passed to UPF (NOTE 3) and provided by UPF to the Service Functions in N6-LAN. | N/A | Optional |
| NOTE 1: When the AF request targets existing or future PDU Sessions of multiple UE(s) or of any UE and is sent via the NEF, as described in clause 6.3.7.2, the information is stored in the UDR by the NEF and notified to the PCF by the UDR.NOTE 2: Internal Group ID can only be used by an AF controlled by the operator and only towards PCF.NOTE 3: The NEF, PCF and SMF do not need to understand the Metadata. |
The PCF checks whether the SFC ID received from the AF corresponds to an authorized predefined SFC according to the service level agreement with this AF. Based on the SFC ID received from the AF, the PCF derives the TSP ID(s) (that can be different for uplink and downlink directions) and sends the TSP ID(s) and optionally Metadata (as provided by the AF) to the SMF as part of the PCC rule(s) as described in clause 6.3.1 of TS 23.503 [45].
The SMF behaves in the same way it is described in clause 5.6.16.1. If the SMF has received Metadata in the N6-LAN Traffic Steering Enforcement Control information of the PCC rule, the SMF forwards the Metadata to the UPF via N4 in the corresponding FAR as described in clause 5.8.5.6.