Re: [Gnu-arch-users] New feature at the mirror + request for help

[Evan Powers]

On Monday 29 March 2004 03:32 am, Stephen J. Turnbull wrote:
>     James> There is a p2p app that you may not be familiar with called
>     James> bittorrent.
>
> Have these guys solved the problems that are pointed out in papers
> like "Why Gnutella Can't Scale.  No, Really"?
> http://www.darkridge.com/~jpr5/doc/gnutella.html
>
> And don't say "it's just a directory information service".  Some of
> the guys I work with (not economists; it's a weird department) do
> cell-phone network theory (and occasionally, practice).  At least in
> that environment, you run into the same kind of problem (basically,
> ping storms trying to find a server) just running a directory service.
> I don't know enough to know if that is worrisome on the Internet at
> the scales we're talking about.

Ritter's results are very interesting, but his mathematics is also very 
focused. It's tied directly to the form of the Gnutella network architecture.

BitTorrent has a completely different architecture; Ritter's math isn't 
general enough to cover it.

The simplest way to prove this is to observe that BitTorrent users never 
forward packets, which would make T=1 and Ritter's result extremely 
uninteresting. Actually, BitTorrent's architecture has a lot in common with 
the Napster architecture Ritter likes.

Now, obviously BitTorrent has its own scalability limits. If you are 
interested, I suggest you read

http://bitconjurer.org/BitTorrent/BitTorrentecon.pdf

Basically, the current bottleneck appears to be the bandwidth overhead of the 
tracker (quite small relative to the bandwidth used for uploading pieces of 
the file), which hasn't yet been reached. The largest known deployments have 
had over 1000 simultaneous downloaders.

Another interesting exercise is to enter the queries [gnutella "can't scale"] 
and [bittorrent "can't scale"] into Google. The first produces about 500 
results; the second produces 12, and all of those are because BitTorrent is 
linked on a page discussing how other things don't scale.

Hope that was informative,
Evan