[BitTorrent] Re: bt2 protocol features

skybuckflying skybuck2000 at hotmail.com
Sat Nov 20 14:35:46 EST 2004



Ok here is my feedback and comments and questions about this :)

--- In BitTorrent at yahoogroups.com, Bram Cohen <bram at b...> wrote:
> After much arguing, cogitating, arguing, and cogitating, the bt2 
protocol
> designs are now further along than they were before.
> 
> Features planned for bt2 -
> 
> merkle hash trees - this is by far the most compelling reason to 
break
> compatibility. Files in a multi-file will each have their own hash 
root.

I have no idea why this is usefull, what is is, how it works, or 
whatever :)

> 
> udp-based tracker protocol (with http-based alternative for those 
who care
> less about bandwidth than convenience)

UDP is pretty difficult ;) 

> 
> tracker redirection - when talking to a tracker, that tracker will 
tell
> you where your primary tracker is (usually the one you just hit) 
and your
> backup tracker is. This will enable (1) dynamic tracker load
> redistribution, and (2) tracker backups. Of course, some smarts on 
the
> tracker are necessary. When trackers are distributed they either 
have to
> send some peers to each other or make sure a seed is on each 
tracker, and
> when using a backup tracker it has to redirect everyone back to the 
main
> tracker when it comes back up again. Since those smarts don't 
involve
> changing the protocol, I'm completely punting on it until later.
> 
> a beefed up peer protocol - there are some subtle changes to the 
state
> machine planned, which are strict improvements but kind of involved 
so
> I'll skip over them now. Also peers will announce which files they 
want to
> enable cross-torrent trading.

Cross-torrent trading ?

Hmm does that mean when multiple torrents happen to have the same 
files inside them ?

> Finally, announcements of having parts of
> pieces will be added, since that's enabled by hash trees. Doing 
that last
> part well requires some smarts, but again the smarts don't change 
the
> protocol so I'm punting.

Hmm.. I dont really see why hash trees are needed... maybe I ll write 
my idea below ;)

> 
> The above are the things I'm convinced are a good idea. Notably 
missing is
> gossip. Too dangerous, may be added later via an extension 
mechanism.

Gossip ?

Sorry I am new to this mailing list :)

> The main sticking point left is how to deal with piece sizes - 
ideally all
> peers should be using the same piece size, but whether that's a 
good thing
> to require and if so (or even if not) how to set it I'm not sure of 
yet.

Well so far the torrent has the piece size in it.

So I guess you mean the problem might be with cross torrents having 
different pieces sizes ?

> Also I'm not sure how to make trackers support scrape functionality 
(or

What is scarep functionality ? :)

> more to the point, I'm not sure how much scrape functionality to 
carry
> over, and in what way). Other than those issues all that's left is 
a whole
> mess of details.
> 
> Rest assured that bt2 protocol will have the same ease of 
implementation
> and reliable compatibilty of bt1. Also rest assured I won't push 
the damn
> thing out until I'm certain it will get feature requests down to a 
dull
> roar for at least a few months.

Funny :)

Bye,
  Skybuck





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