Siemens TC12 Installation, Commissioning And Maintenance Handbook page 163

By checking each OTU in turn and checking the errors it should be possible to
determine where the fault lies or what the next step to take is. If errors are
detected in monitor mode it is best to obtain authority to take all OTUs on that line
off line and re test in Outstation mode.
If the fault appears to lie with the OTUs in the field or the line, then testing at the
OTU using the test will determine if it is the line, the OTU or other OTUs.
Connect the test set to the appropriate line test jacks on the OTU board.
By checking the OTU with the test set in Instation mode then any errors would
indicate a problem with the OTU. Checking in Monitor mode any control error
would indicate a possible problem with the line. Errors in the reply message for the
OTU under test (when there were none during its testing with the ITS in Instation
mode) would indicate interference from the line or other OTUs, check other OTUs
starting with those either side of address of OTU under test.
4.5.3.4 Commissioning a Line
Configure the test set with the appropriate OTU and line details.
Connect the test set to the appropriate line test jacks on the modem boards in the
TC12 Instation cabinet.
With the test set in Outstation mode check each OTU in turn simulate all OTUs on
the line and repeat until all configuration faults are removed. You will have now
ended up with a validated test set configuration for the line. The test set and this
configuration can now be used to go round to each OTU in the field in turn and
together with an Outstation test set and handset for the OTU, it will be possible to
test all of the OTU interfaces prior to connection to the line.
666/HE/43100/000
TC12 Installation, Commissioning & Maintenance Handbook
Page 153 Issue 10