[Olsr-users] Question about hidden node behavior

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Hi!

We have such setup. Three nodes in a line: fri - glinska-9 -
trzaska-12, on same channel, ad-hoc, where fri and trzaska-12 does not
see each other. Between fri and glinska-19 nodes there is ETX 1.0 and
between glinska-9 and trzaska-12 nodes there is ETX 1.0, when those
nodes operate independently from the third node. But thing gets
interesting because fri and trzaska-12 does not see each other.

So what we noticed is, that link from fri to glinska-9 started to
deteriorate once we added trzaska-12 node:

https://nodes.wlan-lj.net/graphs/1559/year

This is graph of link quality to fri node from a perspective of
glinska-9. As you see ILQ started to drop, that is the ratio of
packets that are successfully sent from the glinska-9 to fri node.

If we look at graph of how much WiFi traffic does trzaska-12 produce,
we can see a correlation:

https://nodes.wlan-lj.net/graphs/3842/year

So trzaska-12 produces more and more traffic (users get used to it,
more users find it available, more users are using it...).

And now the question. Why is ILQ deteriorating and not LQ. I would
assume that what is happening is that both fri and trzaska-12 (because
they do not see each other) send packets at the same time to glinska-9
node. So that LQ from fri on glinska-9 node should be low. Why is
opposite? Why would fri node have problems receiving from glinska-9
because of the trzaska-12 traffic?

What is interesting is that ETX between glinska-9 and trzaska-12 is
all the time around 1.0. That means that trzaska-12 does not have
problems sending anything to glinska-9 node, even if (by my
assumption) there are packets conflicts between fri and trzaska-12.

(I am long suspecting that in nodewatcher we have ILQ an LQ turned
around, but after many attempts to find a bug, it seems that code is
correct.)


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