British Telecommunications Public Limited Company

Paul Benyon

David M Rohlfing

Philip M Bull

Ian Horsley

Phil Bull

David Rohlfing

A method is presented of determining whether a digital subscriber line is susceptible to radio frequency interference. The method measures the signal to noise ratio (SNR) margin on the digital subscriber line over a number of 24 hour periods. The measured SNR margin over a given 24 hour period is then compared to a reference function of SNR margin over time (24 hours), where the SNR margin of the reference function is higher during the day and lower during the night, and also repeats daily. A measure of the interference susceptibility is generated based on the degree of similarity between the measured SNR margin and the reference function.

DSL line interference susceptibility

The invention relates to a method of estimating an electrical length of a line, which is the signal loss measured at a predetermined frequency such as 1 MHz, compensated for impairments on the line. Firstly, the H log(f) data representing the attenuation plotted against frequency is gathered for the line. Secondly, data transformation is performed on the H log(f) data, such as by dividing by the square root of frequency. This compensates for changes in the loss as a function of frequency, allowing values of the loss from a broader range of frequencies to be used. Thirdly, data spike removal is performed on the transformed data, removing spikes that can arise from a number of factors such as excessive noise. The resulting data is then used to estimate a value for compensated k10.

Estimating the electrical line length of a digital subscriber line

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).

Fault identification using line attenuations

The invention presents a method of identifying faults on a DSL line, typically intermittent faults arising from unstable joints in the DSL line. The method collects errored seconds data at the DSLAM and at the customer's premises equipment (CPE, typically a home hub or router). The error data collected at the DSLAM are termed near-end errors, and the error data collected at the CPE are termed far-end errors. The near-end and far-end data is then analyzed by applying regression analysis to determine if there is a correlation or match between the two sets of data. Matching data patterns are indicative of unstable or bad joints in the DSL line, and are typically intermittent and located near the customer's premises.

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London, United Kingdom

Paul Benyon