Traditional cell sites are equipped with a ground-based radio connected to tower-mounted antennas by a long run coaxial cable. These cables have high loss and are vulnerable to interference, which negatively impacts maintenance costs and system performance. Wireless networks have evolved to using a remote radio head (RRH) where the radio equipment is connected to the baseband unit (BBU) by a fiber optic cable. With this new architecture comes the necessity for an equally flexible interface between the BBU and RRH. This white paper presents the Common Public Radio Interface (CPRI) technology that is now used in the majority of new installations.