5G Core Network Processing: Service-Based Architecture, SBI & Cloud-Native 5GC
Published June 21, 2026 • 8 min read • Telecom Insights
The 5G Core Network (5GC) represents a fundamental architectural departure from the 4G Evolved Packet Core (EPC). Instead of point-to-point interfaces between monolithic network elements (S1-MME, S1-U, S11, S5/S8, etc.), 5GC adopts a Service-Based Architecture (SBA) where network functions (NFs) communicate via a common Service-Based Interface (SBI) using web-native protocols — HTTP/2, RESTful APIs, and JSON. This architectural transformation enables cloud-native deployment, independent scaling of NFs, and the network slicing that defines 5G's differentiated service model.
Key Takeaway: In 5GC, every NF is both a service producer and consumer. The AMF produces UE context services consumed by the SMF; the SMF produces session services consumed by the PCF. This web of producer-consumer relationships is orchestrated by the NRF — the "DNS of 5GC."
Service-Based Architecture (SBA) Principles
The SBA defines each NF as a set of services exposed through well-defined APIs. Key 5GC NFs include: AMF (Access and Mobility Management), SMF (Session Management), UPF (User Plane Function), PCF (Policy Control), UDM (Unified Data Management), AUSF (Authentication Server), NRF (Network Repository Function), NSSF (Network Slice Selection), and NEF (Network Exposure). Each NF registers its services with the NRF, and consuming NFs discover available producers via NRF queries — enabling dynamic, loosely-coupled NF interaction that simply doesn't exist in EPC.
SBI: HTTP/2, REST, and OpenAPI
The SBI uses HTTP/2 as its transport protocol, replacing the diameter (SCTP-based) and GTP-C protocols of 4G EPC. HTTP/2 provides multiplexing (multiple concurrent requests on single TCP connection), server push, and header compression — key efficiency improvements for the high-volume signalling characteristic of 5GC. The APIs are defined using OpenAPI 3.0 (Swagger) specifications, enabling automated code generation and API validation. TLS 1.2/1.3 provides transport security between NFs. The NRF uses OAuth 2.0 for NF-to-NF authentication and authorisation.
NRF: Service Discovery and Registration
The NRF (Network Repository Function) is the central registry of the SBA. Each NF, upon instantiation, registers its profile with the NRF — including NF type, instance ID, supported services, capacity, and load. When the SMF needs to select a UPF, it queries the NRF with filters (DNN, slice, location) and receives a ranked list of candidate UPFs. The NRF supports NF Set and NF Service Set concepts for grouping equivalent NF instances, subscribe/notify for dynamic updates when NF status changes, and health checks (periodic heartbeats) for liveness detection.
Network Slicing in the 5GC
Network slicing — the ability to create multiple logical networks on shared physical infrastructure — is a core 5GC capability. The NSSF (Network Slice Selection Function) selects the set of Network Slice instances to serve a UE based on the Requested NSSAI provided during registration. Each slice is identified by an S-NSSAI (Single Network Slice Selection Assistance Information) comprising Slice/Service Type (SST — e.g., eMBB=1, URLLC=2, MIoT=3) and an optional Slice Differentiator (SD). NFs can be dedicated to specific slices or shared across slices — the latter being more common in initial deployments for cost efficiency.
Cloud-Native 5GC Deployment
The 5GC is designed from the ground up for cloud-native deployment on container orchestration platforms (Kubernetes). Each NF runs as a set of stateless microservices with persistent state stored in a separate Unified Data Repository (UDR). This enables: horizontal scaling — spinning up additional SMF instances during peak hours; rolling upgrades — updating NF software without service interruption; geographic redundancy — deploying NF instances across multiple data centres with the NRF managing failover; and CI/CD pipelines for rapid NF software delivery. Major vendors (Ericsson, Nokia, Samsung, Mavenir) now offer fully containerised 5GC solutions.
The 5G Core's SBA is arguably the most significant architectural innovation in mobile core network history — transitioning the core from a specialised telecom appliance to a software-defined, cloud-native platform built on web-scale technologies.
