In a method and system for determining the composition of a subscriber loop, the method consists of analyzing the echo responses generated by the transmittal of pulses onto the subscriber loop. In the method, discontinuities along a loop are identified sequentially by comparing the measured waveform to waveforms generated on the basis of a hypothesized topology. The best match for the waveform is identified using a maximum likelihood approach and a maximum a-posteriori probability (MAP) estimator using observed knowledge regarding the loop plant. A multiple path search is also utilized to improve results and reduce computation time. Once the generated waveform that best matched the measured data had been found and a discontinuity identified, the waveform generated is subtracted from the measured data to produce a compensated waveform, which is used to detect the location and cause of the next echo. A calibration method is implemented to further improve data acquisition.