Subject: [p2prg] BT Choking Interval

From: Youmna BORGHOL <[email-masked]>
Date: Thu, 7 May 2009 01:56:48 +0000

Hi Everyone,

I'm new to BitTorrent, I'm trying to modify its peer selection algorithm and I have a question regarding the choking algorithm.

What's the reason the choking interval is 10Sec and the optimistic choking interval is 30sec.

Why would those values be the optimal values?

Thanks for your help,

Youmna

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From: Emin Gün Sirer <[email-masked]>
Date: Thu, 07 May 2009 12:22:59 -0700

Hi Youmna,

There is nothing "optimal" about the BitTorrent protocol. It relies
heavily on various heuristics, including a round-robin choker which
operates ever 10sec and optimistic-unchokes on every third invocation
(30sec). These two values happen to be the default in most
implementations; I believe Bram Cohen arrived at these values through
trial and error. 

By the way, a slight generalization of your question is: why should a
protocol use random unchoking to find good peers in the first place?
There is no principled reason why randomly unchoking peers in a large
swarm is an efficient strategy for forging good pairwise connections.
For an alternative viewpoint on how to design a content distribution
protocol, you can take a look at our Antfarm work at the latest NSDI.
AntFarm does not address this particular problem of peer-discovery, but
it has a different architectural take on the entire protocol and is
optimal in one critical sense, namely, how it allocates bandwidth across
multiple swarms. 

- egs

On Thu, 2009-05-07 at 01:56 +0000, Youmna BORGHOL wrote:
> Hi Everyone,
>  
> I'm new to BitTorrent, I'm trying to modify its peer selection
> algorithm and I have a question regarding the choking algorithm.
> ______________________________________________________________________
> Check out the new Windows Live Messenger Looking for a fresh way to
> share your photos?
> _______________________________________________
> p2prg mailing list
> [email-masked]
> http://www.irtf.org/mailman/listinfo/p2prg