[Olsr-dev] OLSRd 0.5.4 and 0.5.5 with ETT available

[Daniel Nitzpon]

hmmm..  i don't have an easy solution here...

but i wonder how you intend to deal with the underlying issues in other 
algorithms:

* the "collision avoidance" issue also has a "reality factor" built-in: 
if you only consider the speed of a link during times on which airtime 
for this link is available, you will end up extremely over-rating links 
on which generally little airtime is available.

* if you circumvent the "unicast traffic" issue, by only measuring 
existing unicast traffic you may never discover a better alternative 
route due to lack of measurements on it. as lots of real-world scenarios 
have little peer-to-peer-traffic (almost all unicast goes to the next 
internet-gateway and back), it may be a real problem, not just an 
academic one.

in how far do you consider these issues "issues"? any solutions in sight?

greetz,
daniel

Henning Rogge schrieb:
> Am Thursday 13 November 2008 09:59:55 schrieb Daniel Nitzpon:
> 
>  > what about the mechanism with measuring timing of deliberate small/large
> 
>  > IP-packets? why did you drop this version?
> 
> There are two problems with packet-pairs...
> 
> first, WLAN is a "collision avoidance" medium, so WLAN drivers may wait 
> for a longer time until they start to send the package (longer than the 
> whole transmission will take). This waiting time is independant for each 
> package.
> 
> second, the time delay in the operation system between kernel and 
> userspace is sometimes larger than the WLAN transmission time too.
> 
> Maybe you could make packet-pair work by using radiotap header for 
> sender AND receiver (so you know the exact times), but if you have 
> enough CPU power for radiotap you don't need packet-pairs.
> 
> But the most important problem with bandwith measurements is that you 
> can only measure bandwith if there is traffic on the link. So you have 
> to spam unicast packages to each of your neighbors and waste lots of 
> airtime.
> 
> Henning
> 
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