The present invention relates to a loop qualification unit and a method thereof for determining loop parameters describing a topology of a twisted pair loop, having two ends, for a digital subscriber line system, wherein the loop parameters being represented by a vector comprising a receiving member for receiving a measurement of a SELT parameter measured at one end of said two ends and for receiving a measurement of a DELT loop transfer function measured at said two loop ends. The unit comprises a model generator for generating a model for the SELT parameter based on the loop parameters represented by the vector; a model generator for generating a model for the DELT loop transfer function based on the loop parameters represented by the vector; and a processor for determining the loop parameters represented by the vector by minimizing the diffe ren ce between the model and the measurement of the SELT parameter and by minimizing the difference between the model and the measurement of the DELT loop transfer function, whereby the determined loop parameters are represented by the vector that provides said minimizations.