O-CU
O-RAN Central Unit: disaggregated gNB component handling RRC and PDCP layers, deployed at centralized sites with open interfaces to O-DU.
Splitting the old monolithic base station into pieces is what O-RAN is about, and the O-CU is the top slice. It runs the layers that don't need to sit next to the antenna — RRC, which manages the radio connection (setup, handover decisions, security), and PDCP, which handles things like ciphering, header compression and reordering. Because none of that is timing-critical on a microsecond scale, the O-CU can live in a centralised data centre or regional edge site, often pooled to serve many O-DUs at once.
In most designs the O-CU itself splits further into a control-plane part (RRC plus PDCP-C) and a user-plane part (PDCP-U), connected internally by the E1 interface. It talks down to the O-DU over the F1 interface. The practical payoff of pushing it central is cost: you consolidate the expensive compute, run it on commodity servers, and only keep the truly latency-bound functions out at the cell site.
Frequently asked questions
- Is the O-CU the same as the 3GPP CU?
- Functionally yes — the O-CU is O-RAN's name for the gNB Central Unit defined by 3GPP, hosting RRC and PDCP. The "O-" prefix signals that it sits inside the O-RAN architecture and is expected to expose open, standardised interfaces (F1 to the O-DU, E2 to the near-RT RIC) so you can mix vendors. The split into CU and DU is 3GPP; the openness mandate is O-RAN.
Related terms
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