5G Core (5GC)

The 5G Core (5GC) is the packet core network architecture defined by 3GPP from Release 15 onward as the control and user-plane backbone of standalone 5G deployments. It replaces the Evolved Packet Core (EPC) of 4G LTE not through incremental evolution but through a deliberate architectural break: where the EPC was built around monolithic, hardware-bound network functions interconnected by point-to-point interfaces, the 5GC is designed from the ground up around a Service-Based Architecture (SBA) — every network function exposes its capabilities as a set of services over a common HTTP/2 bus (the Service-Based Interface, SBI), and any authorised consumer NF can discover and invoke those services through the NRF (Network Repository Function) without bilateral peering agreements or proprietary protocols. This shift reflects two structural requirements of 5G that EPC could not satisfy: network slicing — the ability to run logically independent end-to-end networks (each with its own QoS, isolation, and lifecycle) on shared physical infrastructure — and cloud-native deployment, where NFs run as containerised microservices on commodity compute, can be horizontally scaled, and are managed by standard Kubernetes-compatible orchestration rather than vendor-specific element managers. The 5GC also enforces a hard separation between Control Plane (CP) and User Plane (UP) — the CUPS principle inherited from 3GPP Release 14 and fully operationalised here — so that the UPF (User Plane Function) handling packet forwarding, QoS enforcement, and traffic anchoring can be distributed to the edge independently of the control logic, enabling ultra-low-latency and MEC scenarios without redesigning the control plane. The architecture is access-agnostic: the same 5GC serves NR (New Radio), eLTE, Wi-Fi (untrusted/trusted non-3GPP access), and fixed-wireless access through a unified N2/N3 reference point toward the access network and a common UE context model in the AMF.

The 5GC control plane is decomposed into discrete, stateless or minimally-stateful network functions, each owning a specific slice of the session and mobility management problem. The AMF (Access and Mobility Management Function) terminates NAS signalling from the UE, manages registration, mobility, reachability, and security context — it is the single CP contact point for the access network (N2 toward the RAN, N1 toward the UE). The SMF (Session Management Function) owns PDU session lifecycle: it selects and controls the UPF (over N4 / PFCP), manages IP address allocation (via UDM or local pools), enforces policy rules from the PCF, and drives QoS negotiation end-to-end. The UPF is the sole user-plane element; it anchors PDU sessions, applies packet detection rules (PDRs) and forwarding action rules (FARs) pushed by the SMF over N4, enforces GBR and non-GBR QoS flows, performs UL/DL traffic measurement for charging, and can function as a PSA (PDU Session Anchor), an I-UPF (intermediate, for multi-homed or ULCL topologies), or a branching point for local offload. Supporting NFs include: the UDM (Unified Data Management) holding subscriber profiles and authentication vectors; the AUSF (Authentication Server Function) executing 5G-AKA or EAP-AKA’ and generating the anchor key KAUSF; the PCF (Policy Control Function) providing per-session policy and QoS rules; the NSSF (Network Slice Selection Function) determining which S-NSSAI and NSI a UE is served by; the NEF (Network Exposure Function) securely brokering capabilities toward external applications and edge platforms; and the NRF acting as the service registry and discovery engine for the entire SBA. Interfaces between NFs on the SBI use OpenAPI 3.0-described REST APIs carried over HTTP/2 and secured with OAuth 2.0 (client credentials grant) and mutual TLS, making the 5GC the first 3GPP core architecture with a formally API-first inter-NF contract.

Standardisation of the 5GC is entirely within 3GPP, principally under SA2 (architecture), SA3 (security), CT1/CT3 (protocol and stage 3), and CT4 (core network protocols and charging). The foundational release is Release 15 (frozen June 2018), which defined the SBA, the full NF set, N1–N14 reference points, 5G-AKA, network slicing with S-NSSAI, and the NG-RAN / 5GC split. Release 16 (frozen July 2020) extended the architecture with URLLC and IIoT enhancements (time-sensitive networking, 5GLAN, ethernet PDU sessions), V2X via PC5/Uu, secondary authentication via DN-AAA, and improvements to slice-aware policy. Release 17 (frozen June 2022) introduced NPN (Non-Public Networks) for private 5G, reduced capability (RedCap) UE support, multicast/broadcast (5MBS), and enhanced slice admission control. Release 18 — the first release branded 5G Advanced (frozen 2024) — brings AI/ML integration into the core via an enhanced NWDAF (serving as both an analytics and model-training/inference platform), network automation (FEAT_NetAuto), ambient IoT, and sidelink relay enhancements. Release 19 (ongoing, targeting 2025–2026) continues the 5G Advanced track with further AI/ML-native NF interactions, enhanced NEF for edge exposure, and early 6G architectural studies. Security architecture is anchored in TS 33.501: the 5GC enforces SUPI concealment via the SUCI mechanism (public-key encryption of the subscriber identity using the home network’s public key, preventing IMSI catchers), mandates NAS integrity protection from the first message, and separates home and serving network security through the SEPP (Security Edge Protection Proxy) on the N32 roaming interface, which applies PRINS (Protocol for N32 Interconnect Security) to mediate inter-PLMN signalling — a structural improvement over the SS7/Diameter trust model of 4G roaming.

Deployment of standalone 5GC has followed a Non-Standalone (NSA, Option 3x) → Standalone (SA, Option 2) migration path for most operators, with NSA — which reuses the EPC and adds NR as a secondary radio — remaining dominant in early 5G rollouts because it preserved existing core investments. By 2025–2026, SA deployments have expanded materially, led by operators in South Korea, Japan, the US (notably T-Mobile), China, and a growing number of European operators, as well as private network deployments where SA’s slicing and local UPF capabilities are the primary value proposition. Cloud-native 5GC — NFs packaged as containers, deployed on Kubernetes (often via CNI-specific Helm charts), and managed through ETSI NFV MANO-aligned or cloud-native orchestration (O2 interface toward O-RAN’s O-Cloud for integrated RAN+core scenarios) — is now the default procurement posture for greenfield SA cores; virtualised NFs on NFVI remain common in brownfield or hybrid deployments. The UPF distribution pattern (multiple UPFs in a ULCL or multi-homed topology, with I-UPFs at the edge anchored by a central PSA) is the primary enabler of MEC (Multi-access Edge Computing) integration, allowing traffic to break out locally at the edge without full N6 hairpin to a central data centre. Commercially, the NF vendors (Ericsson, Nokia, Huawei, ZTE, Samsung, and cloud-native specialists such as Mavenir, Parallel Wireless, and Druid Software) offer both disaggregated (per-NF) and converged (full 5GC stack) packaging; the NWDAF and NEF are emerging as the commercial leverage points for AI-driven automation and platform-as-a-service monetisation respectively. The persistent tension in SA 5GC deployments is between the architectural idealism of fully cloud-native, microserviced, stateless NFs and the operational reality of carriers who need predictable latency, five-nines availability, and regulatory compliance on infrastructure that may run on the same sites as their 4G EPC — a tension that drives most commercial 5GCs toward a pragmatic middle ground of containerised-but-not-fully-disaggregated NFs, with stateful session handling carefully isolated from stateless control logic.

Additional Information

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• 3GPP TS 23.501 – System Architecture for the 5G System
• 3GPP TS 33.501 – Security Architecture and Procedures for 5G System
• ETSI 5G overview