The invention relates to a method and a device for optimised xDSL data transmission. In a data connection with a maximum theoretical data transmission rate RTmax, the maximum currently available data transmission rate RAmax is determined by means of a training procedure between two modems. During the data transmission after a training phase (T), at least one modem determines the difference RDiff between the maximum theoretical data transmission rate for said connection and the maximum currently available data transmission rate RAmax from current measured SNR values and values derived therefrom for the maximum currently available data transmission rate RAmax and, in the case where a threshold value RDiffMax is exceeded, a new training procedure is invoked.