Source : Free On-Line Dictionary of Computing

asymmetrical modulation
     
         A scheme to maximise use of a communications
        line by giving a larger share of the {bandwidth} to the
        {modem} at the end which is transmitting the most information.
     
        Only one end of the connection has full bandwidth, the other
        has only a fraction of the bandwidth.  Normally, which end
        gets the full bandwidth is chosen dynamically.
     
        Asymmetrical modulation was made famous by the {HST} mode of
        the early high-speed modems from {US Robotics}.
     
        (1998-03-13)