OTU3_LOF is an alarm indicating that the frame alignment signal (FAS) is abnormal. This alarm occurs when the frame alignment processing is out of frame (OOF) in three consecutive milliseconds.
Cause 1: The settings of the service type or FEC type are incorrect.
Cause 2: The board that reports the alarm is faulty.
Cause 3: The receive optical power or the OSNR of the local board is abnormal.
Cause 4: The signals transmitted by the corresponding board at the opposite end do not have a frame structure.
Cause 5: The fiber of the transmission line is abnormal.
Cause 6: The dispersion compensation value is excessively great or small.
Checking the causes one by one:
For the TN54NS3 board, the main causes of this alarm are the receive power , OSNR and the dispersion compensation abnormal. But by checking the receive power(-5.7dBm) ,OSNR(the same link ,A site is normal)and the DC(by checking the DCM configuration) are normal.
So, the TN54NS3 board maybe have problem.