EXFO RTU 310-310G IP Services Test Head - Manual (Page 413)

System Tabs
Ethernet Test Module 401
Clock Synchronization
For E1: PCM30, PCM30 CRC-4, PCM31, and PCM31 CRC-4. The default
setting is PCM30.
Alarm Analysis

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: 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.
For E1: The Loss-Of-Frame condition will be assumed when three
consecutive incorrect frame alignment signals have been received.