Method and device for fault location by means of switchable test loops in a digital transmission system

A method for fault location by means of switchable loopback in fixed connections of a digital transmission system, in which a) is brought to be tested hard compound in an out-of-service condition, b) FOG) transmits an exchange side arranged fault location device (instead of the useful signal cyclically and separate instruction sequences and measurement sequences via one of the traffic channels of the arrayed to be tested fixed connection to one (at the output of the network termination NT) at the subscriber region close loop closure device (RTL), and c) the respective command sequence comprises at least a unique signature to identify the loop closure device (RTL) and at least one end command for the opening of the test loop.