Next Generation Evolved NodeB

Description

The ng-eNB (Next Generation Evolved NodeB) is a radio access network node defined in 3GPP Release 15 as part of the 5G architecture. It provides E-UTRA (Evolved Universal Terrestrial Radio Access, i.e., LTE) user plane and control plane protocol terminations towards the User Equipment (UE) and connects to the 5G Core Network (5GC) via the NG interface. The ng-eNB is essentially an LTE base station (eNB) that has been upgraded to support the NG interface, allowing it to interwork with the 5G core. This enables operators to leverage their existing LTE infrastructure while migrating to 5G, providing a smooth transition path.

The ng-eNB is a key component of the NG-RAN (Next Generation Radio Access Network), which also includes the gNB (NR base station). Together, ng-eNBs and gNBs can serve UEs and connect to the 5GC. The ng-eNB supports the E-UTRA air interface, which includes LTE features such as carrier aggregation, MIMO, and dual connectivity. It terminates the E-UTRA protocols (RRC, PDCP, RLC, MAC, PHY) towards the UE and the NG Application Protocol (NGAP) towards the 5GC. The NG interface between the ng-eNB and the 5GC consists of the control plane (NG-C) and user plane (NG-U) parts. The control plane uses NGAP over SCTP, while the user plane uses GTP-U over UDP/IP.

Architecturally, the ng-eNB can be connected to the 5GC via the AMF (Access and Mobility Management Function) for control plane and the UPF (User Plane Function) for user plane. It may also support dual connectivity with a gNB, where the ng-eNB acts as a master or secondary node, enabling tight interworking between LTE and NR. This is known as E-UTRA-NR Dual Connectivity (EN-DC) or NG-RAN E-UTRA-NR Dual Connectivity (NGEN-DC). The ng-eNB also supports network slicing, allowing it to connect to different network slices in the 5GC.

The ng-eNB was introduced in Release 15 as part of the initial 5G specifications. Its definition has remained largely unchanged across Releases 15 to 19, emphasizing its role as an LTE node connected to the 5GC. In Release 20, the definition was changed to refer to 3GPP TS 38.300, indicating a consolidation of radio access network terminology. The ng-eNB is essential for operators who wish to deploy 5G core networks while continuing to use LTE radio access, providing a path to 5G services without immediate NR deployment.

In summary, the ng-eNB is a critical element for the coexistence and interworking of LTE and 5G, enabling a smooth evolution to 5G core networks and supporting features like network slicing and dual connectivity.

Purpose & Motivation

The ng-eNB was introduced in Release 15 to enable LTE radio access to connect to the 5G Core Network (5GC). Prior to 5G, LTE base stations (eNBs) connected to the 4G Evolved Packet Core (EPC) via the S1 interface. With the advent of 5G, operators needed a way to leverage their existing LTE infrastructure while migrating to the new 5G core, which offers improved capabilities such as network slicing, service-based architecture, and enhanced QoS. The ng-eNB solves this by providing an upgraded LTE base station that supports the NG interface to the 5GC, allowing LTE UEs to access 5G services.

The motivation for the ng-eNB also stems from the need for a smooth transition path. Deploying a nationwide 5G NR network requires significant investment and time. By allowing LTE base stations to connect to the 5GC, operators can offer 5G services to users with LTE devices and gradually upgrade to NR as needed. This approach, known as Non-Standalone (NSA) or Standalone (SA) with LTE access, ensures that users can benefit from 5G core features like network slicing and lower latency even before NR coverage is ubiquitous.

Furthermore, the ng-eNB supports dual connectivity with gNBs, enabling tight interworking between LTE and NR. This allows for increased throughput and reliability by aggregating LTE and NR carriers. The ng-eNB also plays a role in network slicing by allowing LTE cells to be associated with specific slices in the 5GC. Overall, the ng-eNB is a key enabler for the coexistence and interworking of LTE and 5G, facilitating a cost-effective and gradual migration to 5G networks.