FOA Guide



Fake OTDR Traces?

FOA gets some very interesting technical questions, but this is a really unique one:

I have been an external plant technician since 1998. I carry out OTDR testing for trunk links, metro, etc. for various operators and private companies.

A few months ago I was given a series of .SOR files from some links. I am sure that these measurements are false and I have been looking for someone for some time who might know how they have done these tests, to unmask the lie and I thought that you might have seen something similar.

What leads me to think that they are false, would be several details, the weight of the file is almost ten times greater than a normal .SOR file. The times of taking the measurements have differences of 4 minutes OE-EO, the losses of the events are exact, in the trace information the averaging time is 0.

I think they use an emulator to make these traces. Have you seen something similar?

Here is one of the traces (Click on the trace for a larger version - right click and open in a new window so you can follow some of the comments below):

Fake OTDR Trace

We sent the traces to a contact at VIAVI who had their technical people analyze the SOR files. Here is what they saw:

It did not take too long for a colleague of mine to agree that these are fake traces. Below is his assessment:

 

Easy to identify :


Noise on trace too regular

Fake OTDR Traces


Stochastic noise too homogenous


Fake OTDR Traces


data table


Distance range cannot be exact to km on each end and is almost never round number like that.


Number of averages never reaches a round number like 18000, and it is not possible to have the exact same numbers from each end. Viavi doesn’t provide nb of averaging but acquisition time.


True on the weight of the sor file - it's too big.


This file is not a Viavi/JDSU file because our detection algorithm cannot re-evaluate the trace – this tells me there is no acquisition points (dB vs. time)


The conclusion is correct. This is a fake OTDR trace created by a simulator.

 


 


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