Is there a method or tool(s) to prove network outages?

William Waites wwaites at tardis.ed.ac.uk
Sun Dec 1 22:02:45 UTC 2013


On Sun, 1 Dec 2013 20:25:36 +0000, Sina Owolabi <notify.sina at gmail.com> said:

    > Its cyclical, but I have not tried to graph/measure its
    > repetition before now...  Body of tidal water..could be

This is speculation until you have measurements, but if this is the
case I'd wager you are having reflected signal interference off of the
water. The water acts like a mirror and as it moves up and down the
reflected signal will move in and out of phase with the main
signal. At certain points you'll get near complete cancellation and
the link will fail.

See section 4 here for some explanations, fig 5 and 6 for what you
could expect the graphs of signal strength, time, link capactity to
look like:

    http://homepages.inf.ed.ac.uk/mmarina/papers/mobicom_winsdr08.pdf

But not having access to the RF part you can't measure this
directly. If you can get tide tables for a nearby location, what you
could do is say that signal strength is 1 if the link is working and 0
if it is not. Measure for a while then scatterplot that against the
level of the tide. If the measurements of 0 group tightly together
in a few spots then you know definitely what is happening. Perhaps
that plot together with a pointer to a nice academic paper would be
enough to convince the provider of what is happening.

What could you do about this?

If you are lucky and the interference does not complete a full cycle
from destructive to constructive and back with the largest amplitude
of the tides that you experience in that place, you could try moving
the antenna up or down. How much depends on the frequency and
distances involved but I'd try 25cm increments up to a couple of
meters if you can. You'll still get degradation but can hopefully
avoid the deep nulls that take the link out completely.

If you are able and willing to replace the end-site radios or antennas
with your own, and the link uses some sort of 2xN MIMO, you could
arrange vertical spacing between the antennas so that you have a good
signal at one antenna when the other one is experiencing a null. This
should get you on average half the best-case throughput the equipment
is capable of but it should get you that consistently. The actual
spacing depends on the distances and heights involved.

-w
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