Service Didn’t Restore After Fiber Cut In SDH
Hi ,
Today I want to share with you a case in SDH network, when a service didn’t restore after fixing fiber cut.
Description
- SDH MSP ring consists of OSN1500-B had a fiber cut between 2 NEs, the fiber soldering team achieved the fiber soldering and the optical signal got received in the line board in both NEs, but NE1 site reported RLOS and the other site NE2 reported MR_RDI in the line boards, we checked the alarm but the alarm persisted.
Optical power received in both ends
As in the power measurement screen the power is -23 in side and -21 in the other, while SFPs are 80km, so the sensitivity is up to -28.
R_LOS alarm in NE1 and MR_RDI in NE2
Problem Analize steps
1- As both sites receives a signal but one side didn’t work, we doubt that there is a mistake in the fiber soldering and maybe the signal come from another system, so we had to make sure that the received signal belongs to the opposite line board, we shut down the laser of NE1 line board, and observed the optical power value in NE2 line board.
But once stop laser in NE1 the optical power in NE2 becomes -60, that means the soldering is correct and the signal received belongs to the same link.
2- Making warm reset for the board reporting R_LOS in NE1, but also no change.
3- Making onsite loop back for the line board reporting R_LOS in NE1 with adding proper attenuator, but also the board kept reporting R_LOS.
Conclusion and solution
-The SFP in the board got faulty and we had to replace it to fix the problem.
-The fiber soldering personnel use an OTDR (Optical Time Domain Reflectometer) this device sends an optical signal in the fiber and measure the time of the reflected light to define precisely the place of the fiber cut, the fiber soldering personnel didn’t follow the work rules and used the working fiber to measure the cut place, and mistakenly sent a strong signal toward the line board and so the transceiver got faulty.
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