EXFO FTB-8100 Series Transport Blazer for FTB-200 - Manual (Page 253)

DSn Tabs
SONET/SDH Application 241
DS3/45M RX
Alarm Analysis
Possible alarms that can be detected are:
³
OOF (Out-OF-Frame): A OOF error indicates that four consecutive
frame bit errors are detected.
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RDI (Remote Defect Indicator): The RDI alarm is declared when both
X-bits of the M-Frame are set to “0”.
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AIS (Alarm Indication Signal): The AIS alarm is declared when the
M-frame contains zeros (0) for C-bits, ones (1) for X-bits, 1010...
repeating sequence with a one (1) immediately following any of the
control bit positions for the information bits.
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Idle (DS3 Idle): The Idle alarm is declared when subframe 3 of the
M-frame contains zeros (0) for the three C-bits, ones (1) for X-bits,
1100... repeating sequence with the first two bits following each control
bit set to 11 for the information bits.