Hi,
Maciej Wojciechowski wrote:
The only thing that is different in this approach from the standard
simulation is that a regular bittorrent client is used. The ISPs
topology, seeders to leechers ratio, upload speeds and so on are
purely artificial. The main problem with bittorrent simulations is not
the inaccuracy of the simulated software but wrong assumptions about
how the network really looks like. With respect to that, the
abovementioned experiment is not much different from "simulating
bittorrent with parameters that have unknown relation to real-world
values". Since much of the bittorrent behavior characteristics remain
unknown (although many great measurement papers have been published)
it is very hard to do credible simulations of protocol performance in
changed conditions.
You are right that you cannot obtain the best of each world.
However, it is plain wrong to claim that our results are equivalent to
what would have been obtained
with simulations, or that our results do not bring any new significant
insight compared to previous works.
I hope that a detailed reading of the paper will convince you. If this
is not the case, I would be pleased to
discuss specific concerns.
As we explain in section 3.2, the results we obtained would have been
hard, if not impossible, to obtain with simulations.
We show that the dynamics of the packets and of BitTorrent algorithms
have a major impact on the inter-ISP traffic savings.
In particular, we found that an initial seed insufficiently provisioned
may increase the inter-ISP traffic in case of locality.
Also, arguing that it is equivalent to run simulations than controlled
experiments makes me feel going back ten years
ago. And yes, running a real BitTorrent client is one of the major
difference compared to a simulation, but I don't
believe this difference can be discarded as a minor one.
If you have specific concerns on the methodology, I would be pleased to
discuss them.
Running in the wild experiments is important, but it just gives one part
of the picture. The other part can only be obtained
running controlled experiments, and varying well chosen parameters.
For instance, even if both Ono and P4P papers significantly improved the
comprehension of P2P locality,
they do not answer all questions (and never claim to do so). However,
there are still some fundamental problems to
explore, as explained in the introduction of our paper.
Regards,
Arnaud.
--
Arnaud Legout, Ph.D.
INRIA Sophia Antipolis - Planète Phone : 00.33.4.92.38.78.15
2004 route des lucioles - BP 93 Fax : 00.33.4.92.38.79.78
06902 Sophia Antipolis CEDEX E-mail: [EMAIL PROTECTED]
FRANCE Web :
http://www-sop.inria.fr/planete/Arnaud.Legout/index.html
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