O-RAN architecture: O-CU, O-DU, O-RU

Disaggregated RAN Components

O-RAN disaggregates the traditional gNB into three components aligned with the 3GPP CU/DU split. The O-CU (Open Central Unit) handles higher-layer protocols: RRC for control signaling, PDCP for ciphering and header compression, and SDAP for QoS mapping. It can split further into O-CU-CP (control plane) and O-CU-UP (user plane), typically deployed in a data center or edge cloud. The O-DU (Open Distributed Unit) handles real-time Layer 2 processing: RLC for segmentation, MAC for scheduling and HARQ, and high-PHY for channel coding and modulation.