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

[Dan O'Keeffe]

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
> 
> 
>