[BitTorrent] BT repeater?

Bill Cox bill at viasic.com
Wed Dec 8 11:56:16 EST 2004


Cool... A BT expert!

I like the idea of exiting a torrent to delete stuff, and then re-
entering to download more useful pieces.

A potentially workable heuristic might be to fill only part of the cache
with needed data, and waiting until they were no longer wanted before
asking for more.  Until the cache size limit was reached, this could
continue, and then enough of the cached pieces could get deleted to make
the overhead of exiting and entering the torrent small in comparison to
what it takes to fill the newly freed portion of the cache.

This might have the additional benefit of having the repeaters become
useful more quickly, before filling their cache.  So, if a guy is
generous and allocates a 10G cache, we don't have to send him that much
before his upload/download ratio skyrockets (thus helping the torrent).

Bill

On Wed, 2004-12-08 at 16:24 +0000, Justin Cormack wrote:
> 
> Any caching system like this does need to modify the protocol (well there
> are ways of getting round it). The basic problem is if you drop a piece
> as you are out of disk space you need to send donthave messages so no one
> asks you for it.
> 
> The alternative is to write a cache that just exits when it needs to make
> more space, deletes some stuff, and then starts up again - this will slow
> downloads in progress.
> 
> In order to not change the wire protocol, it would be possible to simply send a
> new bitmap that overrides the old one at any time, but clients would have to
> be modified to accept this.
> 
> > 
> > 
> > 
> > Hi.
> > 
> > BT suffers from a basic problem: down-loaders of big files typically
> > leave the torrent after downloading.  This leads to an average
> > upload/download ratio of at around 1/1.  Since most of us upload much
> > slower than we download, this is bad.
> > 
> > I think more of us would be willing to leave our BT clients running
> > with lots of torrents open, except that:
> > 
> > - It uses too much disk space to remain in lots of torrents
> > - It is difficult joining and managing lots of torrents
> > 
> > For example, I just upgraded to Linux FC3, and downloaded 2.3G of
> > data.  I burned the DVD, and had to remove the data to save disk
> > space.  I might be willing to donate upload time to another torrent
> > with smaller files, but which one?  I cannot simply look at a list of
> > web links and predict the torrent that would benifit the most.
> > 
> > I think both of these problems can be solved.  In particular, I think
> > that a modified client could do the job without modifying the BT protocol.
> > 
> > In effect, I'm suggesting writing a BT repeater in a multi-cast
> > system.  Of course, IPv6 already does this, but that might not become
> > real for many years.
> > 
> > Here's how I imagine the modified client working:
> > 
> > - The client would automatically download all .torrent files from a
> > list of user-supplied .torrent file servers.
> > - The client would examine the various torrents to find ones that
> > needed additional bandwidth.
> > - The client would enter the torrent(s) that need it's bandwidth the most.
> > - To limit space on the hard-drive, only a user-specified sized cache
> > would be used for writing pieces of files.  A typical cache might be
> > from a few MB to a few hundred MB.
> > - The client requests a set of least-available file pieces from it's
> > torrents, but only enough to fill up the cache.
> > - The client downloads these pieces, and then servers them up to its
> > torrents.
> > - When a file piece is no longer in demand, the client deletes it, and
> > downloads a new piece that is in demand.
> > - When a torrent no longer needs the repeater function, the client
> > leaves it, and joins the torrent that needs it the most.
> > - When the user of the client requests a file download, the repeater
> > function gets suspended until the requested file is fully downloaded.
> > 
> > What do you think?
> > 
> > Bill Cox
> > 
> > 
> > 
> > 
> > 
> > 
> > 
> >  
> > Yahoo! Groups Links
> > 
> > 
> > 
> >  
> > 
> > 
> > 
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>  
> Yahoo! Groups Links
> 
> 
> 
>  
> 
> 
> 
-- 
Bill Cox <bill at viasic.com>
ViASIC



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