Service-Based Architecture (SBA) in the 5G Core

The 5G Core (5GC) introduces a revolutionary shift in design compared to legacy mobile cores. At the heart of this change lies the Service-Based Architecture (SBA), which transforms the way network functions interact, communicate, and scale. Instead of relying on rigid, point-to-point interfaces, SBA leverages a service-oriented approach, making the 5GC more flexible, modular, and cloud-ready.

What is SBA?

In simple terms, SBA turns 5G Core functions into services that can be discovered and consumed on demand. Each Network Function (NF) exposes its capabilities via standardized APIs over HTTP/2 or RESTful interfaces, instead of fixed, predefined connections.

This makes the 5GC similar to modern IT cloud platforms, where services can be dynamically invoked, scaled, and upgraded without disrupting the whole system.

Key Network Functions in SBA

Some of the critical 5GC NFs that operate in an SBA model include:

• AMF (Access and Mobility Management Function): Handles registration, mobility, and connection management.

• SMF (Session Management Function): Manages PDU sessions and IP address allocation.

• UPF (User Plane Function): Forwards user data and anchors sessions.

• PCF (Policy Control Function): Applies policy rules and QoS for different slices.

• UDM (Unified Data Management): Central subscriber database.

• NRF (Network Repository Function): Service registry where NFs register their capabilities and discover others.

• NEF (Network Exposure Function): Exposes core capabilities securely to external applications and third parties.

Interfaces in SBA

Unlike legacy cores (4G EPC) that used fixed interfaces like S1, S5, S11, SBA uses service-based reference points:

• Nxx Interfaces (point-to-point): For user plane and some control plane interactions.

• Service-Based Interfaces (SBI): HTTP/2-based APIs allowing NFs to request services from each other dynamically.
  For example, the AMF can discover and communicate with the SMF through the NRF rather than relying on a fixed interface.

Added Value of SBA

1. Flexibility and Modularity: Functions can evolve independently, allowing faster upgrades and innovation.

2. Dynamic Discovery: With NRF, NFs discover services in real time instead of static provisioning.

3. Cloud-Native Readiness: SBA is built for virtualization and containerization (VNFs and CNFs).

4. Scalability: Individual NFs can scale horizontally without affecting others.

5. Service Exposure: NEF enables new business models by exposing APIs to third-party developers.

6. Resilience: If one NF instance fails, another can take over seamlessly through service discovery.

Conclusion

The Service-Based Architecture (SBA) is the foundation of the 5G Core’s cloud-native design. By replacing rigid point-to-point connections with flexible, API-driven services, SBA enables operators to deliver customized slices, scale efficiently, and open their networks to new ecosystems. In short, SBA transforms the 5GC into a platform for innovation, bridging telecom with IT cloud practices.