Could Skype Be Pure P2P?
With the Great Skype Outage heading into its second day with no clear end in sight, pundits like Om Malik are wondering aloud whether the very idea of P2P architectures is flawed:
Folks at Joost, Babelgum and other P2P companies should be concerned about their business prospects going forward. Venture capitalists who have been funding P2P-based services should take this as an early warning on the fragility of the whole P2P ecosystem, where a small glitch can cause widespread problems.
To be fair, Om has since backpedaled on this. (Side note: if an AllPeers rep every says “We love our customers too much to let that happen,” please put them out of their misery.) The actual P2P parts, if correctly implemented, are incredibly robust. By avoiding centralized points of failure, the system can continue running even if large swaths of it go offline. However, some things are much, much easier to implement with a central server. Skype’s registration server, for example, is a centralized service that keeps track of who is registered, what contacts they have, basic profile information and the like (at AllPeers we do the same). I’m not sure how their name resolution works, but you need a way to find out the IP address of a given node (e.g. your buddy Bob) and that’s much easier to accomplish with a server as well.
Basically your network has a P2P part which, for all intents and purposes, can never go down, and a centralized part which is subject to all the same scalability and availability considerations as any pure client/server solution.
So could Skype (or any P2P network) replace its centralized infrastructure with P2P technology that makes downtime a thing of the past? For someone like Skype, who already has a huge and fairly stable P2P overlay network, the answer is probably yes. I would keep the centralized servers but mirror the registration and name resolution data on a Distributed Hash Table. In essence, you figure out which Skype nodes are up most reliably (there must be thousands of people whose Skype uptime is near 100%) and use them to hold a mirror to the data on the servers. The servers would be there to make sure that data isn’t lost if someone goes offline unexpectedly, but otherwise the DHT would be used and no one would even notice if the centralized boxes went down for some time period.
As it transpires, Om’s second article quotes Skype as saying the problem is actually a result of an error in their networking code. The real question is thus whether EBay is an effective steward of what was for a long time a true technical marvel: incredibly reliable, fast, simple and easy to use. Judging from recent Skype releases, I’m not that optimistic.
UPDATE: The New York Times has more details about what caused the outage. If the problem has existed in the software since 2003 then maybe I was a bit harsh on EBay.
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Chandan
Director
damaka, inc
damaka id: chandan
Comment by Chandan — 8/17/2007 @ 8:40 pm