Introduction

Skype(available at http://skype.com) is a multi-purpose client thatprovides voice communication features as well as standard instant messaging features such as textmessages and file transfers. The company highlights the voice communication features, and it is oneof the most popular applications for making and receiving Internet-based calls. Skype sarchitecture resembles many peer-to-peer (P2P) services. This should come as no surprise, since itsfounders, Niklas Zennstr m and Janus Friis, were also the creators of Kazaa, one of the mostpopular P2P services. Rather than transmit all data for voice communication through a centralserver, Skype has the ability to use the workstations signed into the system to transfer data toand from callers. This allows the service to handle data efficiently while keeping costs minimalfor scaling the service. The Skype program saw its first beta release on August 29, 2003. ByOctober 2004, Skype had over one million users online simultaneously, and on May 18, 2005 had threemillion users online at once. Obviously, Skype has become incredibly popular in a very short amountof time. Of course, much of this popularity has to do with the fact that Skype provides free voicecommunications. Rather than pay fees to telephone companies for calls made to others, Skypeprovides a way to communicate with others, no matter where they are located in the world, for free.Additionally, the sound quality of these calls is very good, due to both efficient compressionalgorithms and the peer-to-peer nature of the network, which provides ample bandwidth for carryingthe large amounts of data for voice communication. Skype also provides...