[p2p-hackers] Error correcting codes to prevent failure in BitTorrent like systems?

[Arnaud Legout]

Hi,

Nick Johnson wrote:
>
> This is why I'm after stats, not guesses - I'm of the opinion that 
> even with rarest first, the chances of getting every single block are 
> very low (remember, if you have 1000 blocks, and you're 99% likely to 
> have each block, that's still only a 0.004% chance you'll have them 
> all). However, that's just my guess, and this is just yours - only 
> stats will show it one way or the other, really.
>
and we have stats. You can have a look at (section IV-B):
http://hal.inria.fr/inria-00000156/en

for an experimental evaluation of rarest first. We are still working on 
this paper and more results are to come.
However, they all show that rarest first increases the entropy of the 
pieces in a way that renders more complex
piece management pointless in all the torrents we monitored.

In particular, rarest first increases very fast the rarest pieces in 
your peer set so that the probability to have rare pieces in your peer
set decreases fast with time. Therefore, even if some peers leave the 
peer set, the chance to have missing pieces is low.
Of course, you have transient period of time during which some pieces 
may disappear from the torrent. But in a typical torrent,
this is unlikely.

Do not hesitate to comment or ask questions on our paper, I would be 
pleased to answer.

Regards,
Arnaud.