[BitTorrent] BT repeater?

Bill Cox bill at viasic.com
Mon Dec 13 10:51:58 EST 2004


> >> The downside is that it costs more bandwidth.
> >
> > A slave repeater could stop helping other slaves when it's helped them
> > download some predetermined amount of data.  After that, it just helps
> > out enough to know that it should be able to get that much back at some
> > time in the future.  So, the total upload/download ratio remains around
> > 1:1.  You only pay for about as much upload bandwidth as you download.
> > But, you get the download bandwidth when you need it, not limited by
> > your upload bandwidth.
> 
> If from the outside, your ratio is 1:1, then each slave uploaded on average 
> the same as it downloaden to the 'world'.
> But that means the data is not yet at the master.
> So transfering that data to the master is the extra bandwidth (cost). 

I got a chance to think a bit more about this...  There's something that
might happen that could be pretty cool.

If a bunch of slaves come to your aid, they all achieve about a 2:1
upload/download ratio, and you benefit from that.  However, that leads
to a the extra cost in terms of upload bandwidth required to get
download credit with other slaves.  As I said in the last post, you'd
wind up having to upload twice as much data as you download, making file
transfers more expensive than a normal bittorrent download.

However, there's no reason that a slave couldn't help out multiple
masters that are trying to download from the same torrent.  For example,
when RedHat releases FC4, if there were 100 masters trying to download,
and 500 slaves there to help them out, each slave could download a least
available piece to as many of the masters who wanted it as possible.
This could help the slaves achieve upload/download ratios far higher
than 2:1, reducing the overhead cost getting download credit with other
slaves.  With enough masters downloading in parallel, the overall cost
to transfer files with the help of slaves approaches that of a normal BT
transfer.

What I think is cool about this is that not only does it make it
possible to get download credit cheaper, it gives us a selfish motive to
do the right thing: go find a torrent that needs your help badly and
help out, acting as an efficient repeater.  I'm also pretty excited that
the whole slave protocol seems to be a direct result of the original BT
protocol.  It's kind of like watching a game-of-life screen-saver.
Start with something simple and watch it evolve.

Bill




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