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RE: 100basefx SFP issue [7:131854] posted 07/08/2008
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Hi Sachendra,

I've not seen this problem specificly before, however I have seen something
very similar with optical transmission equipment. Typically the root cause
would be that the received power level is right on the operating boundary
(too high, or too low). Disconnecting the cable and reconnecting it again
often allows each end to lock on to the signal and then, in time, it loses
it in the noise. Too high really isn't an option in your case as the maximum
output from a 100baseFX sfp is below the maximum input. Too low initially
would seem unlikely as the spec allows for a 2km span, which obviously is a
little more than the 500m that you believe to be the case. However ... there
are a few possibilities:

1) Incorrect fibre - using multi-mode fibre on a single-mode port can lead
to some really interesting issues ... and of course no-one ever suspects the
fibre because it's not something that you can see remotely
2) Dirty/Damaged/Bent fiber - the losses that can result from treating a
fibre like coax can easily be the source of low power at the receiver. Your
"fiber guys" should be able to confirm this very quickly though by measuring
the receive power level ... -33dBm is pretty much the limit
3) Bad SFP - potentially on either side but "best guess" would be the one
that stays up!

Option 4 of course is that there's another problem that has nothing
what-so-ever to do with the physical layer and the switch itself is just
demanding attention!

Good luck!

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