[p2p-hackers] paper "rarest first and choke algorithms are enough"

Bob Harris bob.harris.spamcontrol at gmail.com
Thu May 4 14:45:45 UTC 2006

Personally, I don't get these "X is enough, no need for Y"
claims for software
(X = bittorrent as is, Y = coding in this case). If you
can have X _and_ Y, that's clearly better than X. Someone
else is going to implement Y, and they'll do it just
once, so it's no skin off of anyone's
back. The two cases mentioned below (even though they are not
in steady state) seem like ample justification for coding.


On 5/4/06, Daniel Stutzbach <agthorr at cs.uoregon.edu> wrote:
> On Thu, May 04, 2006 at 11:04:40AM +0200, Arnaud Legout wrote:
> > We identified that when the performance of a torrent is not optimal,
> > then it is in a transient phase. That means that the seed has not yet
> > sent a copy of each piece. If you use network coding of whatever coding
> > you can imagine, we will not improve that fact that information is
> missing
> > in the torrent and that is this missing information that causes the
> > decrease in performance.
> Coding may be able to recover the missing information more quickly
> when the system is in a transient phase.  I can think of two scenarios
> where this may occur:
> 1) Early in the life of the torrent when the seed has uploaded each
>    piece only once or twice.  However, due to the fact that many users
>    abort their downloads, some of these uploaded pieces will be
>    missing and the seed does not know which pieces were reproduced
>    into the rest of the system and which were not.  Coding
>    may allow the system to get out of the transient phase more rapidly
>    since the seed does not risk uploading redundant information.
> 2) Late in the life of the torrent when all the seeds have departed.
>    Coding improves the probability that the set of remaining
>    peers have enough information among themselves to reproduce the
>    whole file (and become new seeds), thus extending the life of the
>    torrent.
> --
> Daniel Stutzbach                           Computer Science Ph.D Student
> http://www.barsoom.org/~agthorr                     University of Oregon
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