ration of the UE association via logical Xn connection. This identifier is included in all UE- associated XnAP signaling. SgNB UE XnAP ID is used to uniquely identify the UE over Xn interface within a SgNB for dual-connectivity. The MgNB stores this identity for the duration of the UE-associated logical Xn connection. This identifier is included in all UE-associated XnAP signaling. gNB-CU UE F1AP ID uniquely identifies the UE association over the F1 interface within the gNB-CU. gNB-DU UE F1AP ID uniquely identifies the UE association over the F1 interface within the gNB-DU. gNB-DU ID is configured at the gNB-DU and is used to uniquely identify the gNB-DU within a gNB-CU. The gNB-DU informs the gNB-CU of its gNB-DU ID during F1 setup procedure. The gNB-DU ID is used over F1AP procedures. 1.2.1.3 User-Plane and Control-Plane Protocol Stacks This section describes an overview of the NG-RAN protocol structure, protocol layer termi- nations at various access and core network nodes, as well as the functional split between the NG-RAN and the 5GC. The NG-RAN radio protocols can be divided into control-plane and user-plane categories, where the user-plane protocols are typically responsible for carrying user data and the control-plane protocols are used to transfer signaling and control information. In general, a communication protocol is a set of rules for message exchange and/or sending blocks of data known as PDUs between network nodes. A protocol may define the packet structure of the data transmitted and/or the control commands that manage the session. A protocol suite consists of several levels of functionality. This modularity facilitates the design and evaluation of protocols. Since each protocol layer usually (logically or physi- cally) communicates with its peer entity across a communication link, they are commonly seen as layers in a stack of protocols, where the lowest protocol layer always deals with physical interaction of the hardware across the communication link. Each higher layer 5G Network Architecture 