[p2p-hackers] Supernodes in the FastTrack network

Jacob Madsen jacob at mungo.dk
Tue Mar 7 18:31:09 UTC 2006


Hey again

Great answar Saikat - thanks alot!

The stuff about Skype using the FastTrack protocol or something similar
made me wonder. I thought that the whole network wasnt reachable from a
client's point, since the search requests have a time-to-live that is
decremented at each supernode it passes and dropped when the value is
zero (so in the aspect of Skype, not all users can reach eachother,
unless they have implemented the protocol differently)

Thats actually 2 questions and i'm really only interested in the first
about FastTrack and the time-to-live value limiting the reachability of
the search requests.

As far as i remember, the client has 1 connection to a supernode and
send its search requests to that supernode. The supernode send (flood)
its supernode neighbours with the request and the time-to-live value in
the request is decremented at each supernode it passes and will reach
the zero value at some point and be dropped.

Again - thanks in advance!

Saikat Guha wrote:
> On Tue, 2006-03-07 at 17:23 +0100, Jacob Madsen wrote:
>   
>> I was reading about FastTrack [...] almost 3 millions users at the
>> moment.
>> Do someone know of a method to calculate the approx. number of supernodes?
>>     
>
> Bunch of really *rough* estimates.
>
> 1) In [1], the authors claim that roughly 50% of MSN users are NAT'ed;
> such nodes cannot become supernodes [2] (while [2] relates to Skype
> specifically, there is some evidence to suggest Skype uses the same
> underlying network as Kazaa = FastTrack; also, [2] finds roughly 4
> million users, so in the same ballpark). Based on these two, figure
> 1.5--2M  supernodes as an upper bound. My personal intuition is that it
> is much less.
>
> 2) In [2], a crawl of the supernode network identified some 250K, only
> some of which were online simultaneously. The crawl was not exhaustive.
> Figure this is some sort of weak lower bound, with the real number being
> higher.
>
> End result: we don't know for sure, but my guess is somewhere between
> 200K to 2M active supernodes. An order of magnitude doesn't matter much,
> right? :P 
>
> A large-scale crawl should yield some tighter bounds. The crawl
> methodology is written up in [2].
>
> [1] P Rodriguez, See-Mong Tan, C. Gkantsidis, "On the feasibility of
> commercial, legal P2P Content Distribution", In ACM/SIGCOMM CCR, Jan
> 2006. http://research.microsoft.com/~pablo/papers/CCR.pdf
>
> [2] S Guha, N Daswani and R Jain, "An Experimental Study of the Skype
> Peer-to-Peer VoIP System", In IPTPS'06, Feb 2006.
> http://saikat.guha.cc/pub/iptps06-skype/
>
> cheers,
>   
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