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Skype = internet telephony solution that is based on P2P principles



"Skype is a P2P internet telephony network that allows users to talk to other Skype users free. Unlike open VoIP protocols like SIP, IAX, or H.323 the Skype protocol requires no servers and has been found to work across different types of network connections including firewalls and NAT. In addition, Skype also allows users to call traditional telephone numbers or receive calls from traditional phones, and receive voicemail messages." (

Discussion: Skype's use of proprietary P2P technology

From :

""Skype uses a different type of Peer-To-Peer network than most companies -- a proprietary form based on SuperNodes. A SuperNode P2P System is one in which you rely on your customers rather than your own servers to handle the majority of your traffic. SuperNodes are just normal computers which get promoted by the Skype software to serve as the traffic cops for their entire network. In theory this is a good idea, but it does have unique vulnerabilities that have been exposed during the past week. Skype, as a company, has no physical or programmatic control over the most vital piece of its product when the network destabilizes for any reason.

Another issue with SuperNode models concerns system recovery after a crash. A SuperNode-based network can only recover as fast as new SuperNodes can be identified." (


Skype, using P2P filesharing principles for telephony:

Zennström and Friis, the creators of KaZaa, one of the early and popular P2P filesharing systems, came up with the idea of using P2P to enable free phone calls on the internet, and Skype was born, poised for an extraordinary rapid update. Beyond phone calls, users have been creatively tinkering with it to enable audio and video broadcasts (i.e. Skypecasting). Excerpts from an interview in

Business Week:

"Q: Where else could this go, beyond files and people?

A: It could be other resources -- you know, storage, video streams. But this really works on two levels. First there's the peer network, and I've been stressing that because it's the enabler for everything. But then there are the applications. We could not have foreseen -- wow! -- all the things that could be developed on top of P2P. For instance, when we first used peer-to-peer technology, we didn't foresee that we could do voice. It became obvious to us after some time, but when we started we didn't know what the applications would be. But when we applied the technology to various industries, we realized we could create a sustainable competitive advantage. That's because, in the normal system you have a marginal cost for every unit you add. If your network is client/server-based, you have to add a new network card for each new Web server, central switch, and so on. But in a peer-to-peer network, you're reusing the system resources in the network, so the marginal cost of producing a phone call or a file transfer or something else is zero. " (;

More Information

An article explaining the rapid diffusion of Skype, at

Open Source telephony developments for the enterprise market are summarized here at,1759,1823596,00.asp

PC to Phone services such as SkypeOut are reviewed by the New York Times, at; Among the competing services it mentions are :,

Google Talk vs. Skype VoIP, a comparison by Red Herring: