For the downlink signal path, the ROU receives optical signals from the ODU (or OEU) and converts them to RF signals in the Remote Optic (R-Optic) module. The signals move to the Remote Drive Units (RDUs) where they are amplified and filtered to remove out-of-band signals.
The ROU Multiplexer in the remote unit combines RF signals from multiple RDUs and then delivers them to a single antenna port. The process is reversed for the uplink path.