Skype und Supernodes

Einen recht anschaulichen Artikel über die Supernodes bei Skype hat Bruno Guissani im März 2006 geschrieben. Unter anderem beantwortet er die Frage warum im CERN keine Skype-Clients installiert werden dürfen...

"Skype can turn user computers into ‘supernodes’ which route traffic through CERN,” François Grey of CERN’s IT communications team explained in an email exchange: “We have encountered some operational problems as a result.” That’s because Skype’s design is based on peer-to-peer, distributed networking principles. This means that the core functions of the system are decentralized, as is the database of Skype users (the tool that lets you look up other Sykpers and tells the system where to forward a call). The calls are set up and passed on among users, flowing through a chain of computers around the world without traversing any central infrastructure.

That’s good for robustness and scalability -- and for Skype, which can avoid massive investments and add new users at near-zero marginal cost. For the system to work, however, some users have to take over its vital functions: routing traffic and holding portions of the database. In Skypeville, these tasks are farmed out to those users with the most powerful computers and the biggest bandwidth, such as CERN. Skype turns them into supernodes.

Only a fraction of users are elevated to this function--currently some 20,000, according to research presented at a recent conference in the Netherlands by Philippe Biondi and Fabrice Desclaux of EADS. And only a small portion of their bandwidth is supposed to be shared. Skype CEO Niklas Zennström explained it to me in an interview last year: “When you become a supernode you share some of your resources and a little bit of bandwidth, but very little; you won’t notice."

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