Radio access network: the part of a telecommunications system that implements a radio technology (e.g. UTRA, Evolved UTRA, CDMA2000, DECT, GERAN) to access the Core Network. The radio access network conceptually resides between user equipment (i.e. mobile phones and other devices) and the Core Network.
In a centralized, cooperative, or cloud radio access network (C-RAN), the base transceiver station (or eNodeB) functionality can be subdivided between a base band unit (BBU) processing pool and a remote radio unit (RRU) or a remote radio head (RRH) with optical fiber connecting the BBU to the RRU.