Every function is a service.
Every service is discoverable.
The 5G Core replaced the EPC\u2019s web of bespoke point-to-point interfaces with a single service bus. Every Network Function exposes a REST API, registers itself in the NRF, and any other function can find and call it — the software-defined shape that lets the core stay on the ground while the RAN flies.
Point-to-point is out. A service bus is in.
In the EPC every interface was its own protocol — S1, S5, S8, S11, S6a… In 5G every NF speaks the same web-native stack and registers itself, so functions can be added, scaled or relocated independently.
Six nodes, seven differently-shaped interfaces. Each new feature meant a new protocol on a new reference point.
Same six functions, one shared interface. Every NF talks the identical HTTP/2 API and finds peers through the NRF.
Four properties make it “service-based”.
These are the invariants of TS 23.501 §4.2 — the rules every NF obeys so the core behaves like one programmable platform rather than a rack of appliances.
HTTP/2 + JSON
Every service is a REST/JSON API over HTTP/2, defined in OpenAPI 3.0. One transport for the whole control plane.
TLS 1.3 + OAuth 2.0
SBI is mutually authenticated with TLS; producers authorize consumers with OAuth 2.0 access tokens issued by the NRF.
Register & discover
Each NF publishes its profile to the NRF; consumers query the NRF to find a producer — dynamic, not configured.
Stateless NFs
Compute is separated from state (UDSF/UDR), so any instance can serve any request and you can scale horizontally.
How a Consumer finds and calls a Producer.
Every service invocation follows the same four steps, entirely through the NRF. Press Play, or step through them.
Direct, or through a proxy.
3GPP defines two communication models. Both use the NRF to discover producers; they differ in whether a Service Communication Proxy (SCP) sits in the path.
The consumer discovers the producer via the NRF, then calls it directly over SBI. Simplest path; the consumer does its own discovery and load-balancing.
- Consumer → NRF (discover) → Consumer → Producer
- Fewest hops, lowest latency
- Every NF carries discovery & routing logic
A Service Communication Proxy routes requests and can perform delegated discovery, load-balancing and overload control — a service mesh for the core. Consumers stay thin.
- Consumer → SCP → (NRF discovery) → Producer
- Central routing, retries, canary & overload control
- Preferred at scale; hides producer topology
One protocol stack for the whole control plane.
The service-based interface is just the web stack, hardened. That is what makes the 5G core programmable — and routable over a satellite feeder.
Sources & specifications
- TS 23.501 — 5G System architecture · §4.2 SBA
- TS 23.502 — procedures for the 5G System
- TS 29.500 — 5G SBA design · HTTP/2, JSON
- TS 29.510 — NRF services · registration & discovery
- TS 33.501 — SBA security · TLS, OAuth 2.0
- Rel-15 / Rel-16 — direct & indirect (SCP) models