Section: 4.3.2.1 Xn User Plane
Content: The Xn User plane (Xn-U) interface is defined between two NG-RAN nodes. The user plane protocol stack on the Xn interface is shown in Figure 4.3.2.1-1. The transport network layer is built on IP transport and GTP-U is used on top of UDP/IP to carry the user plane PDUs. Figure 4.3.2.1-1: Xn-U Protocol Stack Xn-U provides non-guaranteed delivery of user plane PDUs and supports the following functions: - Data forwarding; - Flow control. Further details of Xn-U can be found in TS 38.420[ NG-RAN; Xn general aspects and principles ]  [17].