[c-nsp] Possible causes for fiber link flap?

Peter Rathlev peter at rathlev.dk
Wed Oct 9 08:31:46 EDT 2013

On Wed, 2013-10-09 at 11:31 +0200, Peter Rathlev wrote:
> All fibers were spliced in a new vault and OTDR showed nothing wrong
> afterwards. We can see the loss/reflection from the splice but it's well
> within tolerances. The total link loss (according to DOM) is 0.6 dB in
> one direction and 2.4 dB in the other direction. Budget should be at
> least around 8 dB.

Several people on and off list points out the 2.4 dB loss is in itself
strange even though it's within the budget. That points towards bad

Another interesting point is that the link flaps are not completely
random. It depends on time of day and from cursory inspection it looks
correlated with when many cars are driving near the area where the
splices are made. This could lend itself to this being a fiber problem.

Only thing that bothers us is that two different pairs in two different
tubes (pairs 1,2 and 43,44) exhibit the exact same symptoms. Which led
us to believe that it was unrelated to the fiber itself.


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