SDH ALARMS

NBP/RTTC-MYSORE
NIRANJAN
Regional Telecom Training Center
MYSORE

SDH Framing StructureSDH Framing Structure
NBP/RTTC-MYSORE

PP
OO
HH
TUG-3TUG-3
TUG-3TUG-3
TUG-2TUG-2 TUG-2TUG-2
TU-12TU-12
TU-12TU-12
2 Mbit/s2 Mbit/s
Stuff
C-12C-12
Overhead (PDH)
VC-12VC-12
Pointer (PTR)
TU-12TU-12
TU-12TU-12
TU-12TU-12
TU-12TU-12
TUG-2TUG-2 TUG-2TUG-2 TUG-2TUG-2 TUG-2TUG-2 TUG-2TUG-2TUG-3TUG-3
VC-4VC-4
VC-4VC-4
MSOHMSOH
AU PointerAU Pointer
VC-4VC-4
SDH Framing Structure
RSOHRSOH
AU-4AU-4STM-1STM-1
NBP/RTTC-MYSORE

SDH ALARMS
• LOS : When NE is unable to receive signal
from other NE , due to fiber break , Tx failure
of other NE,etc .It triggers Loss Of Signal
• LOS is Physical Layer Alarm
• There is no byte in SDH frame to indicate LOS. Its the
transreceiver (SFP) which detects the in coming signal.
• If no light coming to SFP it gives LOS to processor or the
controlling device.
Also when u get BER of orde 1 in 1000 results in LOS
NBP/RTTC-MYSORE

LOS-Loss Of Signal
AIS-Alarm Indication Signal
RDI-Remote Defect Indication
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Probable Causes
ALARM PROBABLE CAUSE
1) STM -N Port loss of
signal OF cable break
Rx optical power beyond thrushhold limit
(local eqpt)
TX forced off (Forced Laser Off at distant
end)
Distant ADM/TM/REG module fault
Distant end power failure
Local RX faulty
NBP/RTTC-MYSORE

SDH ALARMS
• LOF : Assuming that signal is present .
• Next job is to identify STM-1 frame by means
of Nx 6 bytes FAW ( 3 bytes of A1 and
3bytesA2 bytes of RSOH) .
• Else it triggers Loss Of Frame
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LOF-Loss Of Frame
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THE NEXT STEP IS TO FIND WHERE THE VC-4S ARE LOCATED
RELATIVE TO THE FAW.
THIS IS ESTABLISHED BY READING THE ADMIN UNIT (AU)
POINTER TO LOCATE THE J1 BYTE IN THE VC-4 POH.
IF A SENSIBLE POINTER CANNOT BE FOUND, A LOSS OF
POINTER (LOP) ALARM IS RAISED AT THE AU LEVEL.
THIS IS USUALLY REFERRED TO AS AN AU-LOP,
AU-LOP
NBP/RTTC-MYSORE

LOP-Loss Of Pointer
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TU-LOP
The next step is to locate and read the Tributary
Unit (TU) pointer
for the specified TU.
If a sensible pointer cannot be found,
then a LOP alarm is raised at the TU level
NBP/RTTC-MYSORE

AIS (Alarm Indication Signal)
LOS, LOF, and LOP alarms will render the whole
signal unusable.
In this case, the missing or corrupted signal is
replaced by an AIS consisting of continuous binary
1s.
This will produce AIS alarms on all equipment
downstream of the fault
NBP/RTTC-MYSORE

NBP/RTTC-MYSORE

LOS-Loss Of Signal
NBP/RTTC-MYSORE

FERF- Far End Reporting Failure
RAI-Remote Alarm Indication
The NE detecting the fault also sends an indication to the
distant (sending) end that an alarm has been raised.
This raises a FERF alarm at the appropriate level at the
transmitting NE.
Thus, a fault at the MS level will produce an MS-FERF.
At the VC-4 level, it will produce a VC-4 FERF on some
equipment, HO-FERFs.
Some SDH elements refer to a remote alarm indication at
some levels in the hierarchy.
NBP/RTTC-MYSORE

HO FERF- Far End Reporting Failure
NBP/RTTC-MYSORE

LO FERF- Far End Reporting Failure
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BIP-Bit Interleaving Parity
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TIM-Trace Identifier Mismatch
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EXC-Excessive Bit Error rate( > 10x E-3)
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NBP/RTTC-MYSORE

REI-Remote Error Indication
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DEG-Degradation
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UNEQ- UNEQuipped
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TIM-Trace Identifier Mismatch
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PLM-Path Load Mismatch
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LOM-Loss Of Multi frame
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ERROR MONITORING
NBP/RTTC-MYSORE
B1 byte is used to check for errors in the RS.
B2 byte is used to check for errors in the MS.
B3 byte is used to check for errors in the VC-4 path.
V5 byte is used to check for errors in the VC-12 path.

BIP-Bit Interleaving Parity
B1,B2,B3 & B5 bytes are used for Error Detection in
specific section and path .
This is based upon BIP detection mechanism
NBP/RTTC-MYSORE

SDH ALARMS

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