Hi, As many of you may know, Zoobab (Benjamin) organised a Babel meeting in Brussels this last week-end. I couldn't stay until the end (perhaps Zoobab and Pieter can fill us in), but here are a summary of the part I was present at.
First of all, under no circumstances should you stay at the Hotel Ibis Sainte Catherine in Brussels. Please see http://www.pps.jussieu.fr/~jch/ibis-sainte-catherine.html (in French). Second, Gabriel and I have been doing some serious testing of Babel-Z over two hops with two radios. 2.4 GHz A ------- B ------- C ....... ....... 5 GHz We've found that it in this degenerate configuration, it's surprisingly tricky to exhibit the Z effect: (i) when there is no packet loss at all, there is a 1/2 chance that plain Babel will pick the optimum route, thus being just as good as BabelZ. Indeed, there are four possible routes, of which two are optimal. In plain Babel, these routes have the same metric, hence 1 chance in 2 to pick an optimal route. BabelZ will of course pick one of the optimal routes. This doesn't happen with moderate packet loss, when the packet loss is different on the two frequencies, thus making plain Babel choose the bad route. (ii) when there is too much packet loss (more than 20% or so), there is very little interference between the different hops, and hence the optimal and suboptimal routes have almost the same throughput. Hence, our tests in that case show little difference between plain Babel and BabelZ. (iii) Finally, when there is just a little packet loss, plain Babel consistently picks a sub-optimal route, while BabelZ consistently picks the optimal route. In that case, we're witnessing TCP goodputs of 3.5 MB/s for BabelZ against 1.8 MB/s for plain Babel. Our conclusions are as follows. First, BabelZ works as expected, and yields the expected performance -- almost doubling goodput over two hops. Second, the topology that we tested is too simple to give a good test case, we really need to have four routers and three frequencies. All in all, a productive week-end. Thanks again to Zoobab and Pieter for inviting us all. -- Juliusz _______________________________________________ Babel-users mailing list [email protected] http://lists.alioth.debian.org/cgi-bin/mailman/listinfo/babel-users
