A physical layer device includes a cable tester that determines a cable status of a cable and that includes a test module. The test module transmits a test pulse on the cable, measures a reflection amplitude, calculates a cable length, and determines the cable status based on the measured amplitude and...http://www.google.com.tw/patents/US7576548?utm_source=gb-gplus-share專利 US7576548 - Cable tester
