TESTING ARRANGEMENTS OF A DIGITAL SWITCHING SYSTEMS

摘要

To test a digital line from a switching centre to subscriber's apparatus a loopback test method is used, in which a pseudo-random bit sequence is sent from the exchange via the GO path and looped back at a desired one of three points (A, B, C) in the path. After each loopback the bit sequence as it returns is monitored and its condition indicates whether there is an error present. By successive use of the different loopback points a detected error can be located. Generation of the pseudo-random bit sequence uses a feedback shift register, and monitoring is effected by applying the returned bit sequence to a similar feedback shift register whose condition thereafter indicates whether there is an error present. The output of the second register is used, with a counter to so control a third feedback shift register to eliminate errors due to the taps on the second register.