eploy- ments where a high-speed (e.g. fiber) fronthaul transport network is not available. The PDCP-RLC split, as opposed to an intra-RLC split and a few other options considered, was chosen for alignment with the dual connectivity architecture, which follows the same protocol split. The F1 standardized interface between a gNB-CU and gNB-DU(s) includes the F1 User-Plane (F1-U) protocol and control plane F1 Application Protocol (F1AP), which generally follow the same design principles as other RAN interfaces (e.g. Xn and X2): F1-U uses GPRS Tunneling Protocol user plane (GTP-U) as the transport and F1AP uses Stream Control Transmission Protocol (SCTP). F1AP supports: interface management procedures, UE context management proce- dures, RRC message transfer procedures, system information procedures, and paging procedures. F1-U uses the common NR user-plane protocol, which is also used on other NG-RAN interfaces (e.g. Xn). It extends GTP-U with functionalities such as flow control, delivery status feedback, and others. gNB-DU and gNB-CU are managed separately via OAM. Certain information has to be preconfigured in both nodes by OAM when new network nodes are deployed. For example, a gNB-DU must be preconfigured with the transport network address of a gNB-CU, a list of cells it supports, etc. 4.2.2 Market Drivers Most LTE base stations are deployed today as a single physical network node, often con- nected to remote antennas controlling what is sometimes referred to as a "three-sector cell," that is, a single base station often controls three cells covering three sectors. Never- theless, the idea of splitting a base station into separate nodes and centralizing at least parts of the base station functionality (similar to UMTS) has been considered for LTE as well. In such an architecture, a base station is "split" into two network nodes, one "high-level" node deployed in a centralized location serving potentially many "low-level" nodes distributed close to antennas. Such centralization has numerous benefits in terms of 