ment, CoMP with higher spectrum gains, seamless mobility, and resource optimization. Because there are different functional split options, the operator needs to evaluate which of the valid splits are suitable for their deployment requirements and at which locations. For more information, 3GPP TR 38.801 captures the functional split requirements and details the advantages and disad- vantages of each. 5G Transport Architecture The evolution in the 5G RAN toward disaggregation and using functional splits segments the archi- tecture into three main parts: the Central Unit (CU), the Distributed Unit (DU), and the (remote) Ra- dio Unit (RU). Depending on the split of the functions, the transport network needs to support dif- ferent characteristics in the areas of bandwidth, jitter, latency, and time synchronization. Depending on location of the DU function, there are multiple deployment scenarios for 5G NR as part of a CRAN or DRAN architecture. As already described in the preceding section, the interface between the RU and the DU is known as the front-haul network, the interface between the DU and the CU (the F1 interface) is called the mid-haul network, and the interface between the CU and 5GCN core is the back-haul network. Figure 10-29 illustrates the basic four scenarios: Scenario 1: RU and BBU/eNB/gNB (DU + CU) at the cell site location: This is an imple- mentation of a fully distributed DRAN architecture and is a very common deployment for 4G LTE. In this case, the cell site is connected to the core network over a back-haul network. These deployments are very common, especially for macro and rural sites. Scenario 2: Centralized BBU (DU + CU) with RU radio functions at the cell site: In this classic CRAN architecture, the RU connects to the BBU at a centralized BBH over a front-haul network (normally using CPRI). This deployment model is already quite common for 4G LTE deployments in some parts of the world (for example, East Asia) and especially for denser urban areas with higher traffic loads. Scenario 3: The R