a data communication system , comprising a first and a second transceiver coupled together through a transmission channel , the transmission channel having transmission characteristics . a measurement circuit is coupled to the first transceiver for measuring the effects of the transmission characteristics upon a known signal transmitted from the second transceiver to the first transceiver a mapping of the transmission characteristics to a code is made and the code is transmitted from the first transceiver to the second transceiver . a plurality of predetermined filters for use in filtering signals to be transmitted by the second transceiver is selected upon receipt of the transmitted code .