The present invention presents a method of identifying faults in a DSL line using upstream and downstream attenuation measurements, which can be obtained directly from the DSLAM or CPE, thus requiring no specialist test equipment nor disrupting service. A downstream over upstream attenuation ratio is calculated for a line, with calculations repeated over a population of lines. The distribution of ratios, as well as upper and lower thresholds, is determined based on the population. A line is identified as being potentially faulty if it has an attenuation ratio above the upper threshold or below the lower threshold. Specifically, an attenuation ratio below the lower threshold is identified as having a high resistance joint fault (caused by an imperfect connection or corrosion at a joint in at least one of the pairs of a line), and a ratio above the upper threshold as a shunt (caused by degradation of the insulation between the pairs of a line, and often coupled with water ingress).