5G System

Description

The 5G System (5GS) is the comprehensive architectural framework standardized by 3GPP for fifth-generation cellular networks. It is fundamentally structured around two primary domains: the Next Generation Radio Access Network (NG-RAN) and the 5G Core Network (5GC). The NG-RAN consists of gNBs (next-generation NodeBs) and ng-eNBs (evolved LTE eNBs connected to the 5GC), which handle all radio-related functions, including scheduling, radio resource management, and connectivity to user equipment (UE). The 5GC is a cloud-native, service-based architecture (SBA) where network functions (NFs) are implemented as software services that communicate over a common framework, typically using HTTP/2-based service-based interfaces (SBIs). This represents a radical departure from the monolithic, point-to-point interfaces of previous core networks like the Evolved Packet Core (EPC).

At the heart of the 5GC are key Control Plane and User Plane functions. The Access and Mobility Management Function (AMF) terminates the N1 and N2 interfaces, handling registration, connection, and mobility management, but is deliberately separated from session management. The Session Management Function (SMF) is responsible for session establishment, modification, and release, including IP address allocation and policy enforcement for the User Plane. The User Plane Function (UPF) is the packet gateway and router for the data plane, performing packet inspection, routing, forwarding, and applying quality of service (QoS) rules as dictated by the SMF. The UPF also enables local breakout for edge computing and supports network slicing.

Other critical functions include the Unified Data Management (UDM), which stores subscriber data and authentication credentials, the Authentication Server Function (AUSF) for authentication, and the Policy Control Function (PCF) for policy decisions. The Network Exposure Function (NEF) securely exposes network capabilities to third-party applications. The 5GS architecture is designed for flexibility, enabling network slicing—the creation of multiple logical, isolated networks on a shared physical infrastructure—to serve diverse use cases with different requirements on latency, bandwidth, and reliability. The system operates with a clear separation of the Control and User Planes (CUPS), allowing them to scale independently and be deployed closer to the network edge for low-latency services.

Purpose & Motivation

The 5G System was created to address the limitations of 4G LTE and its Evolved Packet System (EPS), which were primarily optimized for mobile broadband. The exponential growth in connected devices, the demand for ultra-low latency applications (like autonomous vehicles and industrial automation), and the need for massive machine-type communications (mMTC) for IoT rendered the previous architecture insufficient. The EPS's monolithic network functions and rigid, point-to-point interfaces made it difficult to innovate, scale efficiently, or rapidly deploy new services.

The primary motivation for 5GS was to build a future-proof, flexible, and efficient network core. By adopting a cloud-native, service-based architecture, 5GS decouples network functions from proprietary hardware, enabling deployment on commercial off-the-shelf servers and in virtualized/containerized environments. This allows for agile scaling, faster service rollout, and reduced operational costs. Furthermore, the explicit design for network slicing is a direct response to the "one-size-fits-all" nature of previous generations, allowing operators to create tailored logical networks for specific vertical industries (e.g., a separate slice for public safety, factory automation, and enhanced mobile broadband) with guaranteed performance characteristics on a common infrastructure.