entral unit (CU), holding base- band functionalities. The traditional Cloud-RAN corresponds to the so-called full centralization. Full central- ization approach provides several advantages. It facilitates upgrade, enabling new features to be added without change in the radio equipment. It is easy to maintain because of the simpler radio equipment, which further lowers the cost on capital expenditure (CAPEX) and operational expenditures (OPEX). A recent trial from China Mobile has shown that OPEX and CAPEX can be lowered by 53% and 30% respectively using Cloud-RAN [3]. In Radio Access Network Slicing and Virtualization for 5G Vertical Industries, First Edition. Edited by Lei Zhang, Arman Farhang, Gang Feng, and Oluwakayode Onireti. © 2021 John Wiley & Sons Ltd. Published 2021 by John Wiley & Sons Ltd. 11 Flexible Function Split Over Ethernet Enabling RAN Slicing addition, the centralized BBUs can be shared and turned off when necessary, potentially reducing energy. It also facilitates the implementations of schemes that mitigate inter-cell interference and ensure effective coordination among adjacent cells, i.e. enhanced inter-cell interference coordination and coordinated multi-point, which significantly improve system capacity and coverage. In full centralization, fronthaul (FH), which is an interface between BBU and RRH, transports data in the form of in-phase and quadrature (IQ) samples over typically common public radio interface (CPRI), Open Base Station Architecture Initiative, and Open Radio Interface protocols, which are open BBU-RRH interfaces. CPRI, created in 2004, was the most adopted for Cloud-RAN Despite the attractive advantages of con- ventional Cloud-RAN, the architecture faces several challenges. The first challenge is the constant data rate of CPRI that is independent of user activity. In fact, it requires continu- ous transport of CPRI stream even if no user traffic is present. The second challenge is IQ data transmission, which requires large bandwidth. The data of one antenna for one car- ri