Why Disaggregate?
Traditional RAN was vendor-locked silicon. O-RAN opens the interfaces so operators can mix vendors: O-RU from one vendor, O-DU from another, O-CU from a third. This breaks vendor lock-in and forces innovation.
Three Nodes · O-CU, O-DU, O-RU
O-CU: PDCP, RRC, SDAP — high-layer protocols. O-DU: RLC, MAC, high PHY (LDPC encode, scrambling, modulation, layer mapping, precoding). O-RU: low PHY (resource mapping, IFFT, CP insertion, RF). The CU-DU split is the F1 interface; the DU-RU split is the open fronthaul.
The 7-2x Split Boundary
In the OFDM transmit chain, the 7-2x split places the boundary between layer mapping (in O-DU) and resource-element mapping + IFFT (in O-RU). This means precoded I/Q frequency-domain samples cross the fronthaul — much lower bandwidth than full time-domain I/Q (CPRI 7-1).
Open Fronthaul · eCPRI vs RoE
eCPRI (enhanced CPRI) uses Ethernet-encapsulated I/Q with TSN for timing. RoE (Radio over Ethernet) is an alternative encapsulation. Both run over standard Ethernet (typically 25G or 100G), enabling COTS switches in the fronthaul network.
Latency Budget · Sub-100 μs
O-DU → O-RU one-way fronthaul latency must be < 100 μs typical (some operators target 50 μs) to meet HARQ timing for FR1 numerologies. mmWave is even tighter. Fiber distance ≤ 20 km is usually feasible.
Beamforming · Where It Lives
Hybrid beamforming: O-DU computes the digital precoder; O-RU applies the analog beam-steering vector (in mmWave). This lets O-DU control multi-user MIMO scheduling while O-RU handles RF beam phasing.
SMO and RIC
O-RAN adds management plane: SMO (Service Management Orchestrator) plus RIC (RAN Intelligent Controller) for AI/ML-driven optimization. xApps (near-real-time RIC) and rApps (non-real-time RIC) provide closed-loop control over scheduling, beam management, mobility.
Frequently Asked Questions
What is the 7-2x split in O-RAN?
A specific PHY split point defined by the O-RAN Alliance. The boundary is between layer mapping (O-DU) and resource-element mapping + IFFT (O-RU). Precoded frequency-domain I/Q samples cross the fronthaul.
What is the difference between eCPRI and RoE?
eCPRI is enhanced CPRI — Ethernet-encapsulated I/Q with TSN timing. RoE (Radio over Ethernet) is an alternative encapsulation. Both run over standard Ethernet 25G/100G.
Why does O-RAN matter to RF/RAN engineers?
It opens the supply chain. Operators can deploy O-RU from one vendor and O-DU from another, breaking vendor lock-in. As an engineer, your skills (PHY, MAC, scheduling) become more portable across vendors.