Abstract: A method and apparatus for transmitting a synchronous data signal (D1) on a transmission medium (2) on which the transmission rate (Y bits/s) is greater than the data signal bit rate (X bits/s). The data signal is converted in a transmitter by over-sampling with a sampling frequency (Y Hz) which is equal to the transmission rate (Y bits/s) on the transmission medium (2), whereafter the data signal (D2) formed by the conversion is transmitted on the transmission medium (2). A clock signal (C2) is formed in a receiver, this signal being phase-locked to the transmitted data signal (D2') and has a frequency (X Hz) equal to the bit rate (X bits/s) of the original, synchronous data signal (D1), subsequent to which the transmitted data signal (D2') is re-sampled with the clock signal (C2) formed in the receiver.