Abstract: A method for cancelling an echo in a network termination (NT) of a transmission system and an apparatus therefor are disclosed. The method comprises the steps of detecting an end of transmission of a specific data train in an up-going signal when the phase of the received clock is to be shifted for synchronization during the transmission of the up-going signal from the NT, shifting the phase of the receiving clock when the end of transmission is detected, sampling a residual echo signal of the echo of the specific data train not cancelled by the adaptive filter, determining a correction value for the output of the adaptive filter and storing the correction value and adding a sign corresponding to the direction of the phase shift to the correction value after the phase shift and adding the result to the output of the adaptive filter to cancel the echo of the specific data train.