EXFO FTB-800 Series for FTB-1 - Manual (Page 260)

Test Results
250 FTB-700G/800 Series
Alarms/Errors
Clock

LOC (Loss Of Clock)
RX: The module is unable to synchronize with the selected Clock
Mode. No valid clock is generated/extracted to/from the EXT CLK port.

LOPPS-L and LOPPS-R (Loss Of Pulse Per Second - Local/Remote) is
only available with Dual Test Set in One-Way Latency measurement
mode.
RX: Either no pulse is received or no pulse is received within 1 second
± 6.6 μs after the previous pulse. LOPPS-R is only monitored once the
DTS connection is established.