This paper introduces the technology of distributed small cell interface known as Common Public Radio Interface (CPRI) for a distributed Base Station (BS) architecture. A distributed BS architecture consists of Base Band Units (BBUs) and Remote Radio Units (RRUs) with interconnection through cables such as optical fibers for network coverage elongation and cost saving. The CPRI is an interface technology for BSs links among the Radio Equipment Control (REC) and Radio Equipment (RE) in BBUs and RRUs. The specification of CPRI defines signaling format and control functions to support various interconnections among network devices of different vendors. CPRI is also expected to be the trend for the next generation of small cell BS.