What Open RAN actually is, how the O-RU/O-DU/O-CU split works, the RIC and its xApps and rApps, and every open interface — grounded in real O-RAN Alliance specifications. A complete, engineer-grade Open RAN resource built by working RAN engineers.
O-RAN (Open RAN) is an open, disaggregated radio access network defined by the O-RAN Alliance. It breaks the traditional single-vendor base station into interoperable building blocks — the O-RU, O-DU and O-CU — joined by open, standardised interfaces, and makes the RAN programmable and intelligent through the RAN Intelligent Controller (RIC).
Crucially, O-RAN is not a replacement for 3GPP. 3GPP defines 5G NR and the functional CU/DU split (TS 38.401); the O-RAN Alliance defines the open interfaces, the RIC and the management architecture that turn that split into a true multi-vendor, AI-driven RAN.
Start with the Complete O-RAN Architecture Guide (built on O-RAN.WG1 OAD), then the honest take in O-RAN vs Traditional RAN.
| Dimension | Traditional RAN | O-RAN (Open RAN) |
|---|---|---|
| Vendor model | Single vendor, end to end | Multi-vendor, mix & match |
| Interfaces | Proprietary fronthaul | Open Fronthaul (7.2x) + open interfaces |
| Intelligence | Embedded, closed | Programmable via the RIC (xApps/rApps) |
| Hardware | Purpose-built appliances | COTS + O-Cloud, virtualised/containerised |
| Innovation | Vendor roadmap-bound | Open ecosystem, third-party apps |
| Trade-off | Simple, proven integration | More flexible, but harder multi-vendor integration |
Deep-dive: O-RAN vs Traditional RAN — the honest comparison.
O-RAN follows 3GPP's 7.2x functional split, dividing the base station into three logical nodes:
| Node | Function | Layers |
|---|---|---|
| O-RU (Radio Unit) | RF + lower physical layer (FFT, CP, beamforming) | Low-PHY |
| O-DU (Distributed Unit) | Higher PHY, MAC and RLC — real-time scheduling | High-PHY · MAC · RLC |
| O-CU (Central Unit) | PDCP, SDAP and RRC — split into CU-CP and CU-UP | PDCP · SDAP · RRC |
The O-RU and O-DU connect over the Open Fronthaul (the 7.2x split), the defining O-RAN interface that lets a radio from one vendor work with baseband from another.
Full walkthrough: O-RAN Architecture Deep Dive · the physical-layer angle: 5G O-RAN physical layer.
| Interface | Between | Purpose |
|---|---|---|
| Open Fronthaul (7.2x) | O-RU ↔ O-DU | The open radio-to-baseband split — the heart of O-RAN. |
| F1 / E1 | O-DU ↔ O-CU / CU-CP ↔ CU-UP | 3GPP CU/DU split interfaces. |
| E2 | Near-RT RIC ↔ O-DU/O-CU | Near-real-time RAN control (10 ms–1 s). |
| A1 | Non-RT RIC ↔ Near-RT RIC | Policies, ML models, enrichment (>1 s). |
| O1 | Managed elements ↔ SMO | FCAPS management & orchestration. |
| O2 | SMO ↔ O-Cloud | Cloud infrastructure management. |
The RAN Intelligent Controller is what makes Open RAN intelligent. It comes in two flavours running on different timescales:
In the SMO, >1 s loops. Runs rApps over A1 — policy, ML training, optimisation.
10 ms–1 s loops. Runs xApps over E2 — traffic steering, interference & mobility control.
Near-real-time RAN apps — the optimisation logic, decoupled from the base station.
Non-real-time apps in the SMO — analytics, policy and AI/ML model management.
Build intelligence: O-RAN xApps & rApps — building RAN intelligence · run it: the O-RAN lab.
The Service Management and Orchestration (SMO) framework manages the whole Open RAN — it hosts the Non-RT RIC and drives the O1 and O2 interfaces. The O-Cloud is the cloud platform (COTS hardware + virtualisation) on which the virtualised RAN functions actually run, managed over O2.
Together they turn the RAN into software running on general-purpose infrastructure — the basis for automation, energy saving and AI-driven operations. See it alongside SDN/NFV in the SDN/NFV lab.
Engineer-grade deep-dives, a hands-on lab, a full course and a book — grounded in O-RAN Alliance and 3GPP specifications.
O-RAN.WG1 OAD v16.
Read →O-RU/O-DU/O-CU in detail.
Read →The honest comparison.
Read →Building RAN intelligence.
Read →Spectrum, vendors, the push.
Read →The 7.2x split, PHY view.
Read →From the 7.2x split to building xApps on the RIC — a full course, a deep book, and a live lab, built by field engineers. Lifetime access from $14.99.