Functional split: CU, DU, RU

Three Units, One Base Station

The gNB protocol stack splits across three functional units positioned at different physical locations. The Central Unit runs PDCP, SDAP, and RRC, which are high-layer protocols tolerant of moderate transport latency, making the CU suitable for centralization in a regional data center. The Distributed Unit executes RLC, MAC, and the upper portion of the PHY layer, all requiring low-latency processing close to the cell site. The Radio Unit performs low-PHY operations including FFT, IFFT, beamforming, and digital-to-analog conversion right at the antenna.