5G Core Overview

The 5G Core (5GC) is the cloud-native control and user plane that anchors every 5G deployment. It authenticates subscribers, manages mobility, establishes PDU sessions, and routes user traffic to data networks. TOSSI integrates the 5GC as the southbound anchor for the RAN and the northbound consumer of cloud-native infrastructure - making it a hub pillar in the open telecom stack.

This pillar covers the 3GPP Service-Based Architecture (SBA): a set of stateless network functions (NFs) that expose REST/HTTP-2 service interfaces and discover one another through the NRF. As a neutral system integrator, TOSSI does not ship its own core - it validates, hardens, and wires together open-source 5GC implementations so they interoperate with multi-vendor RAN, RIC, and orchestration layers.

What this pillar covers

Service-Based Architecture

The control-plane NFs (AMF, SMF, AUSF, UDM, UDR, NRF, PCF, NSSF), the UPF user plane, and the N1–N6 reference points that connect them.

CNF deployment

Packaging and deploying 5GC NFs as Cloud-Native Network Functions (pods) via chart-based packaging or KRM packages on Kubernetes.

SBI interoperability

Validating that NFs from different implementations/vendors register and discover each other correctly through the NRF over a common SBI profile.

Interface hardening

Securing SBI TLS and N4/N3 transport, with a defined migration path to post-quantum cryptography.

Reference cores TOSSI integrates

TOSSI maintains integration recipes and conformance notes for production-grade open-source 5G cores. Each candidate is a Standalone (SA) SBA implementation; the choice depends on language ecosystem, 4G/5G coexistence needs, and production posture. TOSSI selects against capabilities rather than brands - the criteria below define what a viable reference core must demonstrate.

SA SBA core

A 3GPP Release-15+ Standalone core with a clean SBA decomposition (AMF, SMF, AUSF, UDM, UDR, NRF, PCF, NSSF) and an NRF-driven discovery model. The baseline reference profile for labs and integration.

4G/5G coexistence core

An implementation that exposes both a 5G Core (SA) and a 4G EPC, suited to combined 4G/5G testbeds and SA/NSA coexistence work.

RAN-co-developed core

A 3GPP-compliant SA core (AMF/SMF/UPF/NRF/AUSF/UDM/UDR) co-developed alongside an open RAN stack for validated end-to-end open deployments.

Edge-cloud core

A cloud-native, disaggregated mobile core packaged for Kubernetes via chart-based packaging, shaped for production-style edge 5G.

Which core should I start with?

For a first lab, TOSSI recommends starting with an SA SBA core that has a clean service-based decomposition and active open governance, or a combined 4G/5G implementation if you need both EPC and 5GC in one footprint. Choose a RAN-co-developed core when pairing with an open RAN stack end-to-end, and a Kubernetes-native, chart-packaged core when you want a production-shaped edge deployment.

Governing standards

The 5GC is defined by 3GPP. TOSSI’s integration work tracks these specifications and validates implementations against them:

Spec	Body	What it defines
TS 23.501	3GPP	System architecture for the 5G System - the SBA and 5GC reference points.
TS 23.502	3GPP	Procedures and call flows (registration, PDU session establishment).
TS 29.244	3GPP	PFCP over the N4 reference point between SMF and UPF (CUPS).
TS 29.500 / OpenAPI SBI	3GPP	Service-Based Interface realization: REST over HTTP/2, OpenAPI 3, JSON.

How TOSSI deploys the core

The SI deploys 5GC NFs as CNFs/pods, packaged with chart-based packaging or KRM packages, and wires them into the surrounding pillars:

• Southbound to the RAN - N2 (NGAP, gNB↔AMF) and N3 (GTP-U, gNB↔UPF) toward the RAN & O-RAN Integration pillar’s O-CU/O-DU.
• Northbound to OAM - O1/O2 management exposed to the SMO, with lifecycle driven by the Cloud-Native & Kubernetes Operators pillar (KRM-based orchestration and a GitOps controller).
• High-throughput user plane - the UPF’s N3/N6 forwarding is pinned to the eBPF & Dataplane pillar for XDP-accelerated packet processing (e.g. an eBPF-based UPF).
• Security - SBI TLS and N4/N3 IPsec are migrated toward quantum-resistant algorithms per the Post-Quantum Security pillar.

Neutral integration is the deliverable

TOSSI’s value is not a core implementation - it is the conformance harness and integration glue that lets any compliant NF interoperate. The acid test is SBI interoperability across mixed-vendor NFs validated through the NRF.

Explore this section

Service-Based Architecture & Reference Points The control-plane NFs, the UPF user plane, and the N1/N2/N3/N4/N6 reference points.

Deploy a Standalone 5G Core in 15 Minutes Bring up a reference SBA core on Kubernetes via chart-based packaging and verify NRF discovery and a PDU session.

SBI & N4 Interface Reference Lookup reference for the Service-Based Interface and the PFCP/N4 protocol, with governing 3GPP specs.

Roadmap

Planned additions to this pillar: a multi-vendor NRF interop conformance suite, a reference UPF benchmark harness (eBPF/XDP vs userspace fast-path vs kernel GTP-U), and a turnkey GitOps blueprint that deploys a reference 5G core, the SMO, and a Near-RT RIC as one fleet via KRM-based orchestration. These are not yet published.