5G Access Network

Description

The 5G Access Network (5G-AN) is a fundamental architectural component defined in 3GPP's 5G System (5GS). It serves as the umbrella term for the entire access stratum that provides the radio interface and connectivity between User Equipment (UE) and the 5G Core Network (5GC). Its primary function is to manage the radio resources and establish the data and signaling bearers required for communication. Unlike previous generations where the RAN was synonymous with a specific technology (like E-UTRAN for 4G), the 5G-AN is defined in a more abstract and flexible manner to support a multi-RAT (Radio Access Technology) environment.

Architecturally, the 5G-AN is logically separated from the 5G Core via the standardized N2 (for control plane) and N3 (for user plane) interfaces. The most prominent instantiation of the 5G-AN is the Next Generation Radio Access Network (NG-RAN), which consists of gNBs (for NR access) and ng-eNBs (for evolved E-UTRA access). However, the 5G-AN concept is broader and explicitly includes trusted and untrusted non-3GPP access networks, such as Wi-Fi, which can connect to the 5GC via a Non-3GPP InterWorking Function (N3IWF) or a Trusted Non-3GPP Gateway Function (TNGF). This unified access framework is a cornerstone of 5G's convergence goals.

From a functional perspective, the 5G-AN is responsible for critical radio-related procedures. This includes radio resource management (RRM), connection mobility control, scheduling and transmission of user and control plane data over the air interface, and the enforcement of QoS policies received from the 5GC via the N2 interface. It does not perform session management or policy control itself; these are core network functions. Instead, it acts upon the decisions and parameters (like QoS Flow descriptions and Packet Delay Budgets) provided by the Access and Mobility Management Function (AMF) and Session Management Function (SMF). The 5G-AN's operation is governed by the NG Application Protocol (NGAP) over the N2 interface for control plane signaling.

The role of the 5G-AN is pivotal in realizing key 5G performance indicators. It directly impacts user experience metrics like throughput, latency, and reliability. By abstracting the specific access technology, the 5GC can manage mobility and sessions seamlessly across heterogeneous access types (e.g., handover from NR to trusted WLAN), enabling true access-agnostic services. Furthermore, network slicing support begins in the 5G-AN, as it must be able to identify and apply specific radio resource configurations for different network slices based on instructions from the core.

Purpose & Motivation

The 5G-AN concept was created to address the limitations of previous cellular architectures, which were largely built around a single, dominant radio access technology. In 4G EPS, the E-UTRAN was designed specifically for LTE. This created integration challenges for other access types, which were often treated as secondary or external networks. The primary motivation for defining the 5G-AN was to architecturally enshrine the principle of access network agnosticism from the ground up in the 5G System specification.

This approach solves several key problems. First, it future-proofs the 5GS by decoupling the core network design from the specifics of any one radio technology. The core network communicates with 'an access network' via standardized interfaces (N2, N3), regardless of whether that access network uses 3GPP NR, evolved LTE, or Wi-Fi. This simplifies the integration of new radio technologies as they emerge. Second, it enables seamless service continuity and unified policy enforcement across all access types, a requirement for delivering consistent user experiences in a world where devices frequently switch between cellular and Wi-Fi. Finally, it provides a clean framework for network slicing, allowing slice-specific configurations and performance targets to be communicated to and enforced by the underlying radio layer, irrespective of the RAT in use.

Key Features

• Unified abstraction for multiple radio access technologies (3GPP and non-3GPP)
• Standardized control plane (N2) and user plane (N3) interfaces to the 5G Core
• Support for integrated access including NG-RAN (gNB/ng-eNB) and trusted/untrusted non-3GPP access
• Enforcement of core-network-derived QoS policies and Packet Delay Budgets at the radio layer
• Foundation for access-agnostic mobility management and session continuity
• Essential component for realizing end-to-end network slicing across the RAN

Evolution Across Releases

Defining Specifications