These “variable coverage areas” could occur due to distance from our cell towers, heavy network traffic during the time you’re trying to use your phone at the problem location, or even as a result of federal, state, or municipal regulations. That created a huge load on the other supernodes, which crashed them, and so on until the entire system went down.Even though Verizon’s reliable nationwide network covers over 98% of Americans, sometimes there are places where our coverage has gaps, and this can cause your calls to drop or outright fail while you’re at a specific location. Skype calls these super-important directory PCs "supernodes," and the initial Skype client failure-and millions of users restarting Skype at the same time-caused about 25% of them to go down. That means that calls are routed through directories living on the computers of other Skype users. But call setup, routing, and breakdown is handled by the company.īut Skype is a pure peer-to-peer service-as this 2003 paper from Columbia University (PDF) explains, it was actually developed by Kazaa, which is better known for its peer-to-peer file-trading software. Once the call is connected, the clients might begin communicating directly. Most other real-time communications services-Google Voice, public IM services, and corporate IM products like Microsoft's Lync-route connections through centralized servers. So how did a 20% failure become a 100% failure? This is the tricky part. This affected about 20% of all Skype users. But a bug in a version of the Skype software for Windows caused it to choke on the delayed responses from these failed servers. That normally wouldn't have been a problem-the company would simply shut them down and send users to backup servers. As Rabbe explains, the problem started when some servers for Skype's offline instant messaging feature went down.
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