[Olsr-users] Routing problem with bad ETX

[Simon Ebnicher]

Thank you very much for the push in the right direction.
We updated olsrd to 0.6.5.3 (which didn't, of course, solve the problem).
As you suggested, the problem could be solved by modifying the multicast
rate. We didn't know this was something you could change in OpenWrt.
The best tradeoff for our setup was a multicast rate of 6 MBit/s.
5.5 MBit/s still propagates too well and we suspect that the reason is
the different modulation scheme (direct sequence spread spectrum) of
that bitrate.

Best regards,
Simon Ebnicher


Am 2013-04-30 18:04, schrieb Saverio Proto:
> You need to adjust your multicast rate.
> Btw 0.6.3 olsrd is very old. Please use this feed to compile latest version:
>
> https://github.com/openwrt-routing/packages
>
> best regards
>
> Saverio Proto
>
>
> 2013/4/30 Simon Ebnicher <(spam-protected)>:
>> Hi,
>> we have set up a small OLSR mesh network with three routers (TP-Link
>> TL-WDR3600 running OpenWrt 12.09rc1, olsrd 0.6.3). We placed two routers
>> near to each other, and the third router at quite some distance.
>> R1 <----ETX:~1----> R2 <---------------ETX: 1.x to 2.x-----------> R3
>>
>> The ETX on the direct link between R1 and R3 is usually below 2 (about
>> 1.3 to 1.7), so the direct route is preferred. However, the direct route
>> is completely unusable for data transfer (e.g., ping reports >95% packet
>> loss). As soon as two hop route via R2 is used, ping and other traffic
>> works fine.
>> We are wondering why the unreliable link is rated too optimistically. We
>> suspect that the Hello and TC multicast packets (which are used to
>> calculate the ETX) may have a better reception probability than unicast
>> packets (e.g., because they are sent at lower rates, no RTS/CTS). This
>> would lead to ETX values that do not reflect the link accurately.
>>
>> Can anyone confirm or explain this behaviour and maybe offer a solution?
>>
>> Best regards,
>> Simon Ebnicher
>>
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