Perhaps the best way to show what we are talking about is by looking at some numbers. See Fig. 1-3, a graph that combines: the (relative) cost of a silicon wafer as a proxy for chip cost, the number of 3GPP active specifications as a proxy for standards implementation complexity and flexibility, and the operator financial spent on wireless infrastructure over time. The chart shows how the first two (device cost and requirement on flexibility) grow aggressively over time, while the amount of available money for systems development only increases marginally. Clearly, something has to change, and O-RAN is one of the potential solutions to this challenge. Chapter 1 Open radio access network overview On C-RAN, Open vRAN, OpenRAN, xRAN, and Telecommunications Infrastructure Project By now, O-RAN is established as the de facto standard for open, disaggregated, and software-defined 3GPP network implementations. But the O-RAN standards body is not the only (or first) to aim for this goal. A lot of the initial R&D and concept development on O-RAN topics has been done by China Mobile Research Institute (CMRI) under the C-RAN name, where the C stands for Cloud (or, sometimes, Centralized). An initial MOU on C-RAN collaboration was signed in April 2010 between the China Mobile Research Institute (CMRI) and ZTE, IBM, Huawei, and Intel. Six more companies joined in December 2010: Orange, Chuanhua Telecom, Alcatel-Lucent, Datang Mobile, Ericsson, and Nokia Siemens Networks. CMRI hosted the first C-RAN international workshop in 2010. C-RAN targets cloud computing on general-purpose servers in a centralized location for (at the time) 2G, 3G, and 4G communication standards. According to CMRI, colocation of radio equipment in a centralized location allows for resource sharing, leading to significant cost reduction (OPEX: 50%, CAPEX: - 15%). Resource sharing is achieved across stan- dards (use the same hardware to support 2G, 3G, 4G, and now 5G) as well as across radio sites and time (residential district busy-hours are in the weeken