ts of the following: The eNB is a node that supports LTE UE handsets and devices and connects the LTE user plane and control plane protocols to the EPC. The en-gNB is an NR gNB that connects over the 4G RAN to the EPC. In the 5G RAN, the base station has these possible modes: The gNB is a node that supports NR UE handsets and devices and connects the NR user plane and control plane protocols to the 5GCN. An ng-eNB, or next generation eNB, is a node that supports LTE devices and connects the LTE user plane and control plane protocols to the 5GCN. Like the LTE eNB, the 5G gNB is responsible for all radio-related functions: for example, radio re- source management, admission control, connection establishment, security functions, routing the user-plane and control-plane traffic to the 5GCN, QoS flow management, and SO on. In LTE, the eNB-to-eNB connection is handled by the X2 interface and is used for scheduling and coordination. Similarly, in 5G the gNBs coordinate with each other over an Xn interface (similar to the X2 interface in LTE) to support mobility, radio resource coordination, Dual Connectivity, and SO The 5G RAN is designed based on the principle of disaggregating the RAN and transport functions and seeks to unlock the benefits of centralization and virtualization techniques in its deployment. For this reason, it is very important to understand that the 5G RAN defines gNB as a logical func- tion and not a single physical implementation. The 5G RAN supports a functional split between the levels of radio processing to allow the concen- tration of a portion of the RAN processing into a centralized architecture. This gives operators the option to split the RAN function into two parts, the Central Unit (gNB CU) and Distributed Unit (gNB DU), with an F1 interface defined between them. See Figure 10-26 for an illustration of this architecture. 5G NR gNB-CU (((2))) (((2))) gNB-DU gNB-DU (((p))) (((2))) 5G RAN AMF: Access and Mobility Management Function UPF: User Plane Function Figure 10-26 5GCN and RAN Component