What is the Service-Based Architecture in 5G?

In the 5G core the control-plane network functions stop talking over dedicated point-to-point reference points and instead expose RESTful service APIs on a common bus, the Service-Based Interface (HTTP/2 with JSON over TLS). Each NF registers with the NRF on startup, and a consumer discovers a producer dynamically rather than being statically wired to it.

What is the difference between a service-based interface and a reference point in 5G?

A service-based interface (the Nxxx services such as Namf, Nsmf, Nudm) is the API an NF offers on the SBI bus, consumed by whoever needs it. A reference point (N1, N2, N3, N4, N6…) is a named link between two specific endpoints. 5G keeps reference points where the interface is stateful or performance-critical — N1/N2 toward the UE and gNB, N3 for the GTP-U user plane, N4 for PFCP control of the UPF — and uses service interfaces for the rest of the control plane.

What is the role of the NRF in 5G SBA?

The NRF (Network Repository Function) is the registry of the core. NFs register their profile with it on boot and the NRF answers discovery queries, so an AMF that needs an SMF, or an SMF that needs a PCF, can locate a suitable instance at runtime. It also issues OAuth2 access tokens for NF-to-NF authorization.

5G SBA Architecture

An interactive map of the 5G Core Service-Based Architecture. Every NF sits on the common SBI (HTTP/2 + JSON over TLS) bus. Click any box to see its produced services, role and spec references — 3GPP TS 23.501 / 23.502.

SBI — Service-Based Interface (HTTP/2 + JSON)

User Equipment

gNB

RAN

Data Network

N1 (NAS)N2 (NG-AP)N3 (GTP-U)N6

N11 (SBI)

N4 (PFCP)

gNB

User plane

↓ user plane ↓

UE ─ N1 ─ gNB ─ N2 ─ AMF · gNB ─ N3 ─ UPF ─ N6 ─ DN · SMF ─ N4 ─ UPF · AMF ─ N11 ─ SMF

Service-based NF (SBI) Reference-point node (UE / RAN / UPF / DN) SBI bus

Network Function

AMF — Access and Mobility Management Function

Termination point of N1 (NAS) and N2 (NG-AP). Handles registration, connection, reachability and mobility management, NAS ciphering/integrity and relays SM messages to the SMF.

Produced services

Namf_Communication
Namf_EventExposure
Namf_MT
Namf_Location

Spec references

3GPP TS 23.501
3GPP TS 24.501
3GPP TS 29.518

Reference points

Point	Description
N1	NAS signalling between UE and AMF
N2	NG-AP control plane between gNB and AMF
N3	User-plane GTP-U tunnel between gNB and UPF
N4	PFCP control between SMF and UPF
N6	Interface from UPF to the Data Network (Internet / IMS / edge)
N9	GTP-U between two UPFs (I-UPF ↔ A-UPF)
N11	Service-based interface between AMF and SMF

About the 5G Service-Based Architecture

Unlike the EPC, where every node-to-node interaction used a dedicated reference point (S11, S5, S6a…), 5G Core folds its control-plane NFs onto a common service bus. NFs expose RESTful APIs over HTTP/2 with JSON payloads, they register with the NRF on startup, and consumers discover producers dynamically. Reference points still exist where they matter — N1 (NAS), N2 (NG-AP to the gNB), N3 (GTP-U user plane), N4 (PFCP control of the UPF) and N6 (exit to the Data Network) — because those interfaces are stateful and performance-critical.

This diagram is a study aid. Click any NF to see its most common produced services and the TS that defines it. For a deeper dive into the stage-3 call flows, pair it with the 5G Auth Flow Visualizer and SUPI / SUCI Analyzer.

Related tools

How to use the 5G SBA Architecture diagram

Scan the SBI bus. See every control-plane NF sitting on the shared Service-Based Interface across the top of the diagram.
Click a network function. Select any NF box to open a panel describing its role.
Review its services and specs. Read the NF’s produced service operations (for example Nsmf_PDUSession) and the 3GPP TS that defines it.
Trace the reference points. Use the lower part of the diagram and the reference-point table to follow N1, N2, N3, N4, N6 and N11 between the UE, gNB, AMF, SMF, UPF and DN.

Frequently asked questions

What is the Service-Based Architecture in 5G?: In the 5G core the control-plane network functions stop talking over dedicated point-to-point reference points and instead expose RESTful service APIs on a common bus, the Service-Based Interface (HTTP/2 with JSON over TLS). Each NF registers with the NRF on startup, and a consumer discovers a producer dynamically rather than being statically wired to it.
What is the difference between a service-based interface and a reference point in 5G?: A service-based interface (the Nxxx services such as Namf, Nsmf, Nudm) is the API an NF offers on the SBI bus, consumed by whoever needs it. A reference point (N1, N2, N3, N4, N6…) is a named link between two specific endpoints. 5G keeps reference points where the interface is stateful or performance-critical — N1/N2 toward the UE and gNB, N3 for the GTP-U user plane, N4 for PFCP control of the UPF — and uses service interfaces for the rest of the control plane.
What is the role of the NRF in 5G SBA?: The NRF (Network Repository Function) is the registry of the core. NFs register their profile with it on boot and the NRF answers discovery queries, so an AMF that needs an SMF, or an SMF that needs a PCF, can locate a suitable instance at runtime. It also issues OAuth2 access tokens for NF-to-NF authorization.

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