The development of new broadband services over the telephone network requires a good quality of the installation.An important parameter that verifies the quality of a telephone installation system is the symmetry of the line. A measure of the symmetry, made from the telephone exchange center, does not allow remote observation of asymmetry on the client telephone installation.To address this problem, a new method for analyzing the quality of the pair is proposed in this paper. This method consists of evaluating the symmetry of the line by a LF (low frequency) measure made from the telephone exchange side.The aim of this study is to verify the feasibility and the validity of this technique, by a theoretical approach. We have developed a simulation code based on the theory of multi-wire transmission lines, associated with a topological approach. The model and the code are validated using experimental measurements.In the following, we exploit the simulation tool to evaluate this new measurement technique.A second axis of the study was to search for a correlation between the values of LF symmetry evaluated from the telephone exchange side and the values of HF symmetry evaluated at client side.Keywords. quality of a telephone system, symmetry of the cable, multi-wire transmission lines, Defects, ADSL