If you invoke a cable test on a LANCOM router over a line where the remote station is an active partner that is trying to keep the link alive, the cable tester in many cases reports the test result "fail".
The cable tester needs the line to be quiet in order to see how the cable reacts to the pulse. To do this, the cable tester initially terminates the connection.
However, the device at the other end sends link pulses at a certain rate, and these then interfere with the TDR measurement by the cable tester.
The cable test should only be run when the connection over a line is inactive, i.e. it is likely that an error or defect exists.
LCOS version 9.0 (Build 157) the cable test gives the additional status message
link-up . This message is shown when the test was carried out on an active line.