Supernode P2P System
From Aron at http://www.personalbee.com/215/17230826 :
"How is Skype different from other Peer-to-Peer models? According to Aron, like its predecessor Kazaa, Skype uses a different type of Peer-To-Peer network than most companies. Skype uses a system called SuperNodes. A SuperNode Peer-to-Peer 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 the problem happens if your network starts to destabilize. Skype, as a company, has no physical or programmatic control over the most vital piece of its product. Skype instead is at the mercy of and vulnerable to the people who unknowingly run the SuperNodes.
This of course exposes vulnerabilities to any business based on such a system -- systems that, in effect, are not within the company's control.
According to Aron, another flaw with SuperNode models concerns system recovery after a crash. Because Skype lost its SuperNodes in the initial crash, its network can only recover as fast as new SuperNodes can be identified.
Other companies such as SightSpeed that use Peer-to-Peer do not suffer from these flaws that proved to be fatal in this case, since these companies manage and handle all the core functionality themselves. Standards based telephony protocols such as SIP (which SightSpeed uses) were designed from the outset to be fault tolerant." (http://www.personalbee.com/215/17230826)