EXFO FTB-8510B Guia Del Usuario página 1174

System Tab
Clock Synchronization
Alarm Analysis
Note: AIS and LOF alarms are not available for 2MHz clock.
LOS (Loss Of Signal): The LOS alarm indicates absence of an input
signal or an all-zeros signal is received.
AIS (Alarm Indication Signal): The AIS alarm is declared when an
unframed all-ones signal is received.
LOF (Loss Of Frame):
For DS1: The LOF alarm indicates that there was no valid framing
pattern for 40 milliseconds and there was at least one OOF error during
this period.
For E1: The LOF alarm indicates that three consecutive incorrect
frame alignment signals have been received.
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With SF Framing: The Loss-of-Frame condition will be assumed
when 2 terminal frame and/or signaling frame errors in 5
consecutive frames have been received.
With ESF Framing: The Loss-of-Frame condition will be assumed
when 2 FPS frame errors in 5 consecutive frames have been
received.
FTB-8100 Series Transport Blazer