Abstract: The invention relates, inter alia, to a method in which, by reducing the spectral power density in an underfrequency range (UB) of a transmitting/receiving unit, the fact that the underfrequency range (UB) should not be used to send data is indirectly transmitted. This method is particularly suitable for xDSL processes.

Abstract: The invention relates to a method for pre-qualifying subscriber connection lines for broadband services. According to said method, a mathematical characterisation of the physical behaviour of the subscriber connection line is obtained by applying a signal to the subscriber connection line to be tested and the output signal is then observed. Conclusions concerning relevant parameters of the subscriber connection line are inferred from said mathematical characterisation with the help of a classical physical models. A combined time-frequency representation, the Weil transformation according to “A. Weil, Basic Number Theory, Grundlehren der mathematischen Wissenschaften, Bd. 144, Springer 1985”, is used to obtain a statistically solid estimation of the aforementioned mathematical characterisation.