Introduction
The WDM attributes includes several important parameters which make changes in the signal format and affect the service like FEC , Line Code , Wavelength.
Description
– As we come to re-arrange a 100G boards connections between the core equipment OSN9800 U32, we moved connection of the 100G board U402 in NE1 to another peer new board in NE2 and also changed the optical cable path between the 2 NEs, but the link went down and OUT_LOF alarm got reported in NE1 also R-LOS alarm raised in the NE2.
– We didn’t change the board and port in NE1, the change was only in NE2, so we started to check the problem in NE2.
OTU4_LOF reported in NE 1
R-LOS reported in NE2
The problem cause
– Starting with checking the optical power in both ends as R-LOS means that signal is out of receiver range, and we could find a high attenuation caused by optical FC/FC Adaptor, the R-LOS disappeared from NE2 after replacement for the adaptor but OTU4_LOF raised instead.
– Then checking the version of the board, the new board in NE2 was the same hardware and software version of the previous board.
– After that we checked the FEC Working state and both were the same (SDFEC2).
– We checked the manufacturer report to compare the CFP in boards, the CFP were DWDM Tunable type, that lead us to think of the wavelength of the signal, eventually the cause was that the Wavelength of the signal is different between the two ends, all the alarm cleared once fix the frequency to the same value.
The type of CFP is Tunable
– Note that Tunable Coherent receiver can accept any wavelength even if it is not the same wavelength it sends, you just need to define the intended received wavelength in the(receive Wavelength) field.
Conclusion
– Although the 100G boards were connected directly using dark fiber (not using DWDM), the frequency in both ends need to be set equally otherwise the service got interrupted.
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