ve standardized this evolution and named it enhanced CPRI (eCPRI). On the other hand, many industry participants and standards development organizations are propos- ing other (packet-based or optical) technologies to replace CPRI, which will have the additional ad- vantage that it is open and interoperable between vendors. One of those is the O-RAN Alliance, but there are others (see Chapter 4). Beyond bandwidth inefficiency, CPRI also has a very strict delay budget. In practice, this need for low-latency interconnect requires that for CRAN every RU component must be within a certain ra- dius from the BBU. Even moving away from CPRI to a packet-based system like eCPRI, this re- quirement will still be there-there are still latency requirements between the BBU/DU and the RU in the 5G packet-based RAN. 5G RAN The 5G RAN architecture includes measures to ensure backward compatibility, enhanced spectrum efficiency, greater energy efficiency, and reduced cost of deployment. Further, to support the evolu- tion toward the 5GCN architecture, the 5G RAN is designed to support both SA and NSA deployments. Figure 10-25 shows how elements of both an LTE and a 5G RAN architecture work together with either a 4G EPC or a 5GCN. Again, notice that the terminology is quite different between the two architectures for both the control plane (c) and user plane (u) connections. en-gNB en-gNB E-UTRAN ng-eNB ng-eNB 5G RAN EPC-assisted NSA architecture MME: Mobility management entity AMF: Access and Mobility Management Function SGW: Serving gateway UPF: User Plane Function Figure 10-25 5G RAN Architecture In the LTE architecture, the eNB connects to the mobility management entity (MME) to terminate the control plane and to the serving gateway (SGW) for the user plane. Similarly, in the 5G NR ar- chitecture, the 5G version of the eNB (the gNB) terminates the control plane interface at the Access and Mobility Management Function (AMF) and user plane at the User Plane Function (UPF). In the LTE assisted architecture, the base station consis