Open Fronthaul

Open fronthaul is the interface that decides whether O-RAN actually delivers on its promise of mixing radio vendors. It sits between the O-DU and the O-RU, built on the 7.2x split, and it's the one O-RAN interface where the timing is genuinely unforgiving — frequency-domain samples have to arrive slot after slot inside microsecond-scale budgets, or the radio can't transmit correctly.

It's not a single pipe but a set of planes, and knowing them helps when something breaks:

• U-plane — the user data, the IQ samples themselves.
• C-plane — control, telling the O-RU how to handle each slot (scheduling, beamforming descriptors).
• S-plane — synchronisation, the timing/PTP that keeps O-DU and O-RU phase-aligned.
• M-plane — management, for bringing the O-RU up and configuring it.

It replaces the old CPRI link, whose rigid, near-proprietary nature was a big reason classic RAN was vendor-locked. The catch is that "open" hasn't meant "plug-and-play" in practice — interoperability testing between a third-party O-RU and O-DU, especially around beamforming and the M-plane, is where a lot of integration effort still goes.