[Olsr-users] Discrepancy between ETX value and ping packet loss

Henning Rogge (spam-protected)
Wed Mar 18 06:28:29 CET 2015


that is the reason... many mesh networks increase the basic multicast
rate to 6 MBit/s to ignore the old 802.11b rates.

Henning Rogge

On Tue, Mar 17, 2015 at 11:06 PM, Dan O'Keeffe <(spam-protected)> wrote:
> Hey again,
> Actually it's ok, I figured it out. Because the OLSR HELLO messages are
> broadcast at the 1Mbps data rate for 802.11, they experience a different
> packet loss to the 11Mbps unicast traffic.
> Cheers,
> Dan
> On 17/03/15 20:43, Dan O'Keeffe wrote:
>> Hello,
>> I'm trying to use the OLSR ETX extensions to determine the path quality
>> to different destinations (so my application can send data to the
>> destination with the best path as the quality changes over time).
>> However the ETX values I'm seeing don't seem to correspond particularly
>> well to the packet loss I observe when I manually ping the different
>> destinations.
>> More specifically, I have a two node network with each node running
>> olsrd and one node pinging the other (using a ping payload size of 0
>> so that the actual ping is just a 28 byte header). At a certain distance
>> the ping packet loss goes to 40%, but the ETX I observe using the
>> txtinfo plugin is 1.000 (i.e. from the output of 'echo "/all" | nc
>> localhost 2006).
>> Does anyone have an idea as to why I'm not seeing any packet loss
>> affecting the ETX? Using tshark I can see the OLSR control
>> messages being sent and received. However it's hard to tell whether
>> any of the control messages are actually being dropped, and so
>> I'm not sure whether the issue is that the OLSR control messages just
>> aren't experiencing packet loss or I haven't configured the ETX
>> calculation properly. From what I understand the ETX calculation should
>>  be based on the number of hello messages sucessfully sent and received
>> over a sliding window, but perhaps there's more to the implementation?
>> The output of olsrd --version is:
>> *** olsr.org -  0.6.3-git_-hash_e334b612adcb7c22239a9dcafaf5b7ba  - ***
>>  Build date: 2013-03-28 03:47:37 on marid
>> I have made a few tweaks to the default config (see attached), but
>> I don't see that they should make a difference.
>> Finally, I should note that I'm running in an emulated environment
>> (using the CORE EMANE wireless network emulator). The only way I could
>> see that making a difference is that perhaps the same packet loss isn't
>> being applied to broadcast traffic as to normal traffic, but before I
>> check that on the CORE EMANE mailing list I'd just like to be sure there
>> isn't an obvious issue with my olsrd configuration.
>> Thanks for any help!
>> Dan
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