[Olsr-users] Question about hidden node behavior

[KB Patel]

Do you have info on the receive power at "glinska-9" from the 2 nodes.  
If the signal from "fri" is weaker than the signal from "trrzaska-12", 
it could contribute to the behavior you are seeing.

kb

On 01/14/2011 06:30 AM, Mitar wrote:
> Hi!
>
> So we have found a bug in our monitoring code which was parsing LQ in
> ILQ swapped. Hurray for the theory.
>
> OK. So the story is now like this: once we added trzaska-12 node
> (which has a good link in both direction to glinska-9 node), packets
> from fri node to glinska-9 node start getting lost. Probably
> trzaska-12 and fri node does not see each other transmitting.
>
> The question is why only in one direction packet loss is increased. So
> why packets from trrzaska-12 to glinska-9 are also not lost when fri
> transmits at the same time.
>
> I added RTS/CTS of 200 bytes on all three nodes and there is no
> perceived improvement of users using it to access the Internet. ETX
> has not changed (as it uses broadcast/multicast). Ping packet loss
> from the nodes to the central server seems to have even increased
> (maybe just for larger than 200 bytes packets, I will need more data
> to see if it is just a temporary fluctuation).
>
> Maybe we could also try fragmentation.
>
>
> Mitar
>
> On Thu, Jan 6, 2011 at 8:23 PM, Mitar<(spam-protected)>  wrote:
>> 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.)
>>
>>
>> Mitar
>>


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