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

[coderman]

On 12/4/05, Nick Johnson <arachnid at notdot.net> wrote:
> ...
> But statistically, if n different peers each have random subsets of the
> data, the chances of them having 90% of the file between them are much,
> much higher than the chances of them having 100%.

you are assuming there was at least one complete distribution.

in the situation you describe (last seed leaves) some of the remaining
peers do then become seeds as they obtain requisite missing chunks to
complete the torrent, if the remaining peers have the blocks required
to complete what is missing.  i don't see how error codes would be an
improvement (considering coding overhead / expansion), unless the
distribution of blocks using the current bittorrent algorithm was
heavily weighted somehow. (is it?)

if a complete copy has not been distributed within the group then it
doesn't matter what encoding mechanism you use, and in my experience
this has been the usual cause of partial failures.