Source : Free On-Line Dictionary of Computing

in-band
     
         (bit-robbing) The exchange of call control
        information on the same channel as the telephone call or data
        transmission.  Since one bit in a frame is periodically used
        for signalling instead of data, this is often referred to as
        {bit robbing}.
     
        This is the reason why a {D1} channel in the T-carrier system
        can only carry 56 Kbps of usable data instead of the 64 Kbps
        carried by the {D0} channel in the E-carrier system.
     
        (2000-03-10)