On Wed, 1 Apr 2009, Dean Willis wrote:
On Mar 26, 2009, at 10:53 PM, Salman Abdul Baset wrote:
Your alternate solution is an assumption that the overlay will contain
enough TCP open-access nodes that are able to identify themselves as
open-access nodes and willing to bear the burden of their role on
behalf of all the other peers. What I've seen is that UDP actually
works, and TCP doesn't.
Skype works. It has enough nodes that can provide relay services.
The Skype operators apparently pay to put their supernodes into places from
which they can provide relay services. This isn't inexpensive.
You have funding to support RELOAD supernodes?
I don't. I am a Ph.D. student -:)
Just to be clear, I was refering to the relaying of RELOAD messages and
not the media. An insight from our Skype analysis is that the Skype
application fails to join the Skype network if it cannot establish a TCP
connection with any Skype super node.
Nevertheless, relaying of p2p+signaling+media raises some important
issues:
1) Why would Skype pay to put their super nodes into places where they
could provide relay services?
2) How do we know if these 'paid' nodes are being heavily or sparingly
used as media relays?
For (1)
Skype would do that because they do not want calls to fail if they are
unable to find an altruistic Skype node that can relay media. That is just
a smart of designing a system. Failed calls = bad publicity.
For (2)
Clearly, Skype knows this. However, since we do not have this information,
the next best thing is to perform measurements. We performed experiments
where two Skype nodes were forced to select a relay for about ~18,000
calls and we found 9,584 unique media relays. About 46% of calls were
relayed through nodes in educational institutions. These two statistics
seem to indicate that the likelihood of paid Skype nodes being heavily
used as relays is fairly low. Meaning, that Skype has no shortage of
altruistic media relays.
(See slide 8)
http://www1.cs.columbia.edu/~salman/presentations/skyperelay-gi08.ppt
and
http://www1.cs.columbia.edu/~salman/publications/skyperelay-gi08.pdf
I wonder how much money Skype is paying to operators for relay services.
My guess is that it should be significantly smaller than say what MSN
messenger has to pay.
Regards,
Salman
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