What does Skype use the supernodes for, anyway?

I understand peers are used for relaying voice traffic, which is important
to keep bandwidth costs down for the company.

And I understand servers are used for authentication.

However, I recall hearing Skype uses supernodes for such basic operations as
"presence" and rendezvous functions and buddy list management and so on.

Why bother with supernodes for these -- wouldn't it be faster, easier, and
more reliable to just use a few cheap servers?

-david

> -----Original Message-----
> From: [EMAIL PROTECTED] [mailto:p2p-hackers-
> [EMAIL PROTECTED] On Behalf Of Serguei Osokine
> Sent: Tuesday, August 21, 2007 8:57 AM
> To: theory and practice of decentralized computer networks
> Subject: Re: [p2p-hackers] what really happened to Skype?
> 
> On Monday, August 20, 2007 Alen Peacock wrote:
> > ...it seems clear that the author was highlighting the failure
> > of the log-in system as causing cascading failures.
> 
>       The only thing that the author really said was that they
> are sorry. No technical details, no nothing. I hate it when they
> do that. It's like reading a Microsoft press release. At least
> with the Internet failures (flapping and such) you had an analysis
> coming very quickly and publicly; but apparently, not in the era
> of the closed protocols. God forbid someone has a peek into their
> algorithms. No, they should be kept secret.
> 
>       I mean, of course. Otherwise someone might actually learn
> something from that failure and maybe even prevent some similar
> failure in the future. And we cannot allow that, can we, precious?
> 
>       Phew. Sorry for the offtop. Just had to vent. Did I already
> say that I hate this MO?
> 
>       Best wishes -
>       S.Osokine.
>       21 Aug 2007.
> 
> -----Original Message-----
> From: [EMAIL PROTECTED]
> [mailto:[EMAIL PROTECTED] On Behalf Of Alen Peacock
> Sent: Monday, August 20, 2007 3:57 PM
> To: theory and practice of decentralized computer networks
> Subject: Re: [p2p-hackers] what really happened to Skype?
> 
> > Does anyone know much about the Skype P2P/DHT/network algorithm, and
> > can they hypothesize what sort of event could cause it to take so long
> to
> get
> > back into operation?
> 
> Log-in/authentication is centralized in Skype, although distributed
> (http://en.wikipedia.org/wiki/Skype_Protocol).  The Skype post says
> that the restarts "caused a flood of log-in requests, which, combined
> with the lack of peer-to-peer network resources, prompted a chain
> reaction that had a critical impact."
> 
> That remains very nebulous, at least to me.  But it seems clear that
> the author was highlighting the failure of the log-in system as
> causing cascading failures.
> 
> This would make sense, if, for example, peers don't talk to one
> another unless they are already authenticated to the central servers.
> I have no idea if that is true or not, but something of that nature
> could clearly cause the chain reaction described.
> 
> Alen
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