A method for inserting control data in a modulator comprising a plurality of frequency component inputs and a modulator output. The method is performed in the modulator and comprises receiving primary data subcarriers on respective frequency component inputs which are assigned for receiving primary data, receiving at least one control data subcarrier on a respective frequency component input which is not assigned to primary data, combining all frequency component inputs to one output signal, and providing the output signal on the output for transmission to a demodulator over a point-to-point medium.