A method of optimizing the bit rate capacities of DSL user lines subject to far-end crosstalk by adjusting the transmit power spectral densities at the far ends of the user lines by means of parameterized power back-off functions is characterized by the steps of : a) selecting a desired bit rate share for each user line, b) measuring the noise and losses on each user line, and c) determining an individual set of power back-off parameters for each user line by calculating a global sum of the bit rates of all user lines and iterating the power back-off parameters until a maximum value of the global sum is found under the constraint that the desired bit rate shares are met.