I searched for articles on Skype Architecture on google. Here are some of the links that explain the Skype architecture. I found the links to the first two articles at Brad Neuberg's blog - Coding in Paradise
- An Analysis of the Skype Peer-to-Peer Internet Telephony Protocol by Salman A. Baset and Henning Schulzrinne
- An Analysis of the Skype Peer-to-Peer Internet Telephony Protocol
- Challenges And Opportunities in Deploying IPV6 Applications There is fair amount of discussion over Skype architecture in this presentation
Some important points to note about Skype from the above three references:
"Skype is the first VoIP client based on peer-to-peer technology. We think that three factors are responsible for its increasing popularity. First, it provides better voice quality than MSN and Yahoo IM clients; second, it can work almost seamlessly behind NATs and firewalls; and third, it is extremely easy to install anduse."
"Skype architecture is based on stealing someone else bandwidth, without their consent, for other parties to use."