Optical fiber is used for transmission between the BBU and the RRU. The RRU is then connected to the antenna through coaxial cables and power dividers (couplers), that is, the trunk uses optical fiber, and the branch uses the same fiber. AAU, RRU, and BBU are key components in a telecom network, particularly in modern wireless communication systems like 4G and 5G. Here's a breakdown of each: The central processing unit in a base station. In a distributed base station. Here's the sequence of how signals travel from an antenna to the Baseband Unit (BBU), including key information about each step and associated hardware. Think modulation and demodulation, error correction stuff, plus managing protocols across different layers including PDCP, RLC, and RRC. The RRU is normally located at the top of a tower, roof, or similar bu lding object and very close to the antenna.