5.6.16.1 General

Service Function Chaining, also called N6-LAN Traffic Steering, refers to the steering of subscriber's traffic flows to appropriate operator or 3rd party Service Functions (e.g. NAT, antimalware, parental control, DDoS protection) in the N6-LAN.

The content of this clause applies to non-roaming and to Home Routed roaming scenario, i.e. to cases where the involved entities (AF, PCF, SMF, UPF) belong to the Home PLMN and the AF has an agreement with the Home PLMN.

The PCF controls Service Function Chaining by provisioning and modifying traffic steering control information for N6-LAN Traffic Steering as described in TS 23.503 [45], e.g. clause 6.1.3.14. The traffic steering control information for N6-LAN Traffic Steering consists of a traffic description and a reference to a traffic steering policy that is configured in the SMF/UPF.

The PCF derives the TSP ID(s) (that can be different for uplink and downlink directions) based on operator configuration and sends the TSP ID(s) to the SMF as part of the N6-LAN Traffic Steering Enforcement Control information in the PCC rule as described in clause 6.3.1 of TS 23.503 [45].

When the PCC rule is activated or updated with N6-LAN Traffic Steering Enforcement Control information, the SMF sets the Forwarding Policy (uplink and/or downlink) within the FAR(s) based on the authorized TSP ID(s) in the PCC rule and under consideration of the direction. In case that Application Function influence on traffic routing Enforcement Control information and N6-LAN Traffic Steering Enforcement Control information are both provided for the uplink direction, the SMF shall derive N4 rules which instruct the UPF to pass the traffic through the relevant Service Function(s) deployed in the N6-LAN before steering the traffic to the local data network. The SMF provides instructions to UPF for N6-LAN traffic steering as further detailed in clause 5.8.5.6.

The UPF applies traffic steering mechanism based on Forwarding Policy, i.e. the UPF performs deployment specific actions as configured for the Forwarding Policy.

NOTE 1: It is assumed that all UPFs in the operator network serving as PSA for the DNN/S-NSSAI/DNAI subject to N6-LAN traffic steering need to be configured with the same traffic steering information for N6-LAN traffic steering.

When performing deployment specific actions configured for the Forwarding Policy, the UPF may support traffic steering related functionality and user plane encapsulation protocols that are out of 3GPP scope (e.g. as defined by other standards organizations).

NOTE 2: The existing user plane mechanisms (e.g. VXLAN, NSH, GENEVE, GRE, VLAN, etc.) defined at IETF are reused as applicable by the PSA UPF to support N6-LAN traffic steering.

The mechanism used for forwarding the traffic between the Service Functions within the N6-LAN is out of 3GPP scope.