Standalone

Description

Standalone (SA) is a deployment architecture term in 3GPP, most prominently used for 5G, denoting a complete, independent system. In a 5G Standalone (5G SA) deployment, the Next Generation Radio Access Network (NG-RAN), which consists of gNBs transmitting the 5G New Radio (NR) air interface, is connected to the 5G Core network (5GC). This is a clean-slate architecture where both the RAN and the Core are based on the new 3GPP specifications defined from Release 15 onwards. The 5GC introduces fundamental architectural changes like a Service-Based Architecture (SBA) with network functions (NFs) such as the Access and Mobility Management Function (AMF), Session Management Function (SMF), and User Plane Function (UPF). In SA mode, control plane signaling (e.g., registration, authentication, session establishment) and user plane data traffic are handled entirely through these new 5G network functions, without any reliance on the 4G Evolved Packet Core (EPC).

The operation in SA mode unlocks the full spectrum of 5G features. From a control plane perspective, procedures like initial registration, service request, and handover are executed natively between the UE, the gNB, and the 5GC NFs using new protocols like HTTP/2 for service-based interfaces. On the user plane, data flows directly between the UE and the UPF, enabling the ultra-low latency and high throughput promised by 5G. Key capabilities inherent to SA include Network Slicing, which allows the creation of multiple logical, isolated networks on a common physical infrastructure tailored for different service types (e.g., enhanced Mobile Broadband, Ultra-Reliable Low-Latency Communications, Massive IoT). It also fully supports advanced QoS models, edge computing integration via Local Area Data Networks (LADN), and native support for non-public networks.

Contrasting with SA is Non-Standalone (NSA) deployment, initially defined for 5G. In NSA mode (e.g., Option 3x), the 5G NR base station (gNB) is deployed as a secondary cell for data boost, while the 4G LTE base station (eNodeB) acts as the master node providing the control plane connection to the 4G EPC. SA eliminates this dependency, simplifying the network architecture and operations. The transition to SA is a significant step for operators, as it often requires a new core network build-out but is necessary to realize transformative 5G services beyond enhanced mobile broadband, such as mission-critical communications and large-scale IoT. The term 'Standalone' has also been used historically in other 3GPP contexts, such as Standalone GSM cells or Standalone Location Services, but in the modern 5G era, it predominantly refers to the 5G SA architecture.

Purpose & Motivation

The purpose of the Standalone architecture is to realize the complete vision and full capability set of a new generation of mobile technology, unencumbered by legacy system dependencies. For 5G, the motivation for defining SA was to enable services and features that were impossible or inefficient in the Non-Standalone (NSA) mode anchored to 4G. NSA was a pragmatic first step for early 5G deployment, allowing operators to launch 5G services rapidly by leveraging existing 4G core infrastructure, but it could not support core 5G innovations like end-to-end network slicing, ultra-reliable low latency communication (URLLC) with simplified user plane paths, or the service-based core architecture.

SA was created to solve these limitations. It addresses the need for a flexible, cloud-native core network (5GC) that can support diverse service requirements through network slicing—a key differentiator for 5G. It also solves the problem of control plane latency and complexity introduced by the dual-connectivity anchoring in NSA. By establishing a direct control plane connection between the UE and the 5GC via the gNB, procedures become more efficient. Historically, the concept of a 'standalone' mode exists to mark the point where a new technology generation becomes self-sufficient, no longer requiring the previous generation as a crutch. This allows for optimized performance, simplified network management, and the introduction of revolutionary services that define the new generation's value proposition, moving beyond mere incremental speed improvements.