# Architecture

Understand the 5G SA network-function map and interface boundaries.

Product: 5G Core

Human documentation: https://www.1sc.dev/docs/core/architecture

Documentation index: https://www.1sc.dev/llms.txt

## Network functions

| Function | Role |
| --- | --- |
| AMF | Terminates N2, handles NAS registration, and coordinates access and mobility procedures. |
| AUSF / UDM / UDR | Authenticate subscribers and supply subscription data. |
| NSSF / PCF | Select slices and apply session policy. |
| SMF | Creates PDU-session control state and programs the user-plane session. |
| UPF | Terminates N3 GTP-U and handles the supported user-plane traffic path. |
| NRF | Provides network-function registration and discovery. |

## Interfaces

| Interface | Role |
| --- | --- |
| N2 | NG-RAN control-plane signaling between gNB and AMF over SCTP. |
| N3 | User-plane GTP-U between gNB and UPF. |
| SBI | HTTP service-based interfaces between control-plane network functions. |
| N6 / DN | External data-network side of the UPF. General production forwarding is not claimed for the current lab baseline. |

## System boundary

The core owns 5GC control-plane and user-plane behavior. UE, gNB, IMS, OSS/BSS, and external data networks are adjacent systems.

The first supported shape is a single-operator 5G SA lab core, not NSA, EPC, roaming, IMS, charging, analytics, or broad commercial-network operations.