Direct Network Connection

Description

Direct network connection, as defined in 3GPP TS 22.261 and TR 22.865, is one mode of network connection where there is no relay UE between a UE and the 5G network. In other words, the UE communicates directly with the next-generation NodeB (gNB) or the core network via the Uu interface, without the assistance of an intermediate relay node. This is the traditional cellular connection mode, where the UE establishes a radio resource control (RRC) connection with the base station and exchanges user plane data directly.

In the context of 5G and beyond, direct network connection is one of several connectivity options, alongside indirect connections via a relay UE (e.g., UE-to-Network Relay in proximity services). The 3GPP system supports both modes to provide flexibility and coverage extension. Direct connection is typically used when the UE is within sufficient coverage of a gNB, and it offers the benefits of lower latency, higher throughput, and simpler protocol stack compared to relayed connections. It also allows the UE to fully utilize network features such as network slicing, QoS, and mobility management without the relay's constraints.

Architecturally, a direct network connection involves the UE's radio link to the gNB, which is part of the Next Generation Radio Access Network (NG-RAN). The gNB then connects to the 5G core network (5GC) via the N2/N3 interfaces. The UE's data sessions are managed by the SMF and UPF, and its mobility is handled by the AMF. The direct connection mode does not require the relay-specific protocols or the relay UE's processing, which can introduce additional delays and potential bottlenecks.

Key aspects of direct network connection include the ability to support high data rates, low latency, and advanced features like beamforming and massive MIMO. It is the default mode for most UEs and is essential for applications that require deterministic performance. However, in scenarios where coverage is limited (e.g., indoors, remote areas, or in public safety situations), relay connections may be used to extend coverage. The two modes can coexist, and a UE may switch between them based on coverage and policy.

The role of direct network connection in the network is fundamental: it provides the primary means of connectivity for UEs to access 5G services. It is the baseline against which relayed connections are compared, and it enables the full set of 5G capabilities. 3GPP continues to enhance direct connection with features like reduced capability (RedCap) UEs, non-terrestrial networks (NTN), and advanced duplexing schemes.

Purpose & Motivation

The concept of direct network connection exists to clearly define the standard mode of UE-to-network communication without intermediate relays. It was introduced to differentiate from relay-based connections, which are used for coverage extension and other scenarios. By having a precise definition, 3GPP can specify requirements and performance targets for both modes, ensuring that devices and networks can support them appropriately.

Previously, in earlier generations, the term 'direct connection' was implicit, as relay connections were not standardized in the same way. With the advent of 5G and the need for flexible topologies (e.g., for public safety, IoT, and wearables), relay connections became more prominent, necessitating a clear distinction. The direct connection mode serves as the reference for performance, security, and service continuity, and it is the assumed mode for most use cases unless otherwise specified.

The motivation for defining direct network connection is to provide a baseline for network architecture and to enable features like network slicing and QoS that may not be fully supported in relayed connections. It also helps in regulatory and testing contexts, where the direct connection's characteristics are well understood. As 5G evolves, direct connection remains the primary mode, with enhancements focusing on improving its efficiency and capacity.