bove. Another important consideration is the network management, as NR will likely rely on massive small cell deployment alongside macro cells, which creates more challenges in terms of network operation and maintenance. Hence the desire to simplify network man- agement, which becomes significantly simpler with NG-RAN centralization. The usage of CoTS hardware and virtualization in the cloud are not new concepts, as these have been successfully used in the IT industry for over a decade (see Section 6.2). Most of the cloud-building blocks are off-the-shelf standardized equipment, which greatly reduces cost and increases deployment flexibility. On the transport side, the network building blocks including the switches and routers are readily available (see Section 6.6). Moreover, Ether- net has been widely used for long haul and local networks - 100 Gbps Ethernet has been successfully deployed for IT data center networks, which is capable of satisfying the fron- thaul bandwidth requirement. Furthermore, the experiences that the IT industry gained in 4.5 Lower-Layer Split cloud network implementations could help with cloud-based NG-RAN. All these factors made RAN ripe for centralization and virtualization, and indeed during LTE, the service operators and equipment vendors made efforts to find technical solutions for cloud RAN implementations. However, these implementations have been mostly based on proprietary technologies. With 4G, different scale levels were considered for virtualization, ranging from virtual RAN, which uses the virtualization technology on radio network, to distributed RAN, which separates the RAN processing unit into multiple nodes, to cloud RAN, which uses the cloud native technology for RAN. However, these implementations were mostly confined to trials and there have not been massive cloud RAN deployments in LTE SO far. Even though 3GPP considered the physical layer NG-RAN split options during the Release-14 study on 5G (3GPP TR 38.801), this technology was not selected for standard- ization. T