The Technical Report studies and performs evaluations of potential architecture enhancements to enhance the support of service function chaining in the 5G Core network (5GC). Specifically, two objectives are included: WT#2: Investigate whether traffic steering policy is sufficient to support SA WG1 requirements in TS 22.101, TS 22.261 and TS 22.115, study whether and how to define Service Function Chaining (SFC) policies, and investigate solutions and procedures for the 5G network with SFC capabilities to identify/detect/classify user plane traffic and steer the traffic to a chain of ordered service functions for SFC processing in non-roaming and home routed roaming scenarios. WT#3: Depending on the outcome of WT#2, specify possible enhancement to northbound APIs for allowing an AF to request network capability exposure functionalities, e.g. request a service function chain for a certain traffic flow, etc. based on service level agreement with the third party.

The following documents contain provisions which, through reference in this text, constitute provisions of the present document.

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The concept of the SFC is as shown in Figure 4-1 and the following assumptions are applied in this study:

• Each service function (SF) is an opaque processing element in user plane. The SF forwarder, and SF behaviour/control are out of scope of this study that reuses the features defined by IETF for these purposes.
• The initial classification for the service chain to be applied to traffic flow is performed by 5GC.
• The management aspects of SFs, service function paths (SFP), and service function chains are out of scope of the present TR.
• Several service function chains can be simultaneously applied within 5GC of an operator network to meet various business requirements with third parties based on service level agreements. A traffic flow of a PDU Session is subject to a single SFP at a given time.
• The definition of terms and mechanisms in RFC 7665 may be re-used when applicable.
• The study targets the use of traffic steering concept, e.g. defined by 3GPP (FMSS) and SFC mechanisms defined in IETF when applicable. Especially the study aims at reusing user plane mechanisms (e.g. VXLAN, NSH, GENEVE, GRE, VLAN, etc.) defined at IETF to support SFC, as applicable.

For all objectives, the architectural assumptions and principles include:

• Solutions shall build on the 5G System architectural principles as in TS 23.501, including flexibility and modularity for newly introduced functionalities.
• Service path (i.e. for traffic handled by the service functions) is traversed over N6 after PSA UPF(s) in 5G network.
• The case where SFC would apply for a Home Routed roaming PDU Session at an offloading point in a VPLMN is not considered in this study.
• Existing (per 3GPP Rel-17) deployments flexibility should be preserved in deployments of SFC in 5G network.