"Our work suggests the attack on this small fraction of highly loaded computers may make the entire network collapse."

Cascading Failures Could Crash the Global Internet
"For networks where loads can redistribute among the nodes, intentional attacks can cause the entire or a substantial part of the network to collapse," mathematics researcher Adilson Motter and electrical engineering professor Ying-Cheng Lai claim in a new paper on the topic published by Physical Review E.

"Our work shows that in continuously growing networks like the Internet, some nodes become naturally more important than others," Motter told NewsFactor. "From a global perspective, the important nodes are those with exceptionally high loads, which are not necessarily those with the largest number of connections."

Only a few thousand computers, for instance, transmit the bulk of information over the multimillion-computer Internet, Motter explained. "Our work suggests the attack on this small fraction of highly loaded computers may make the entire network collapse," he said.

Diversity: Bad for Networks?

The Internet possesses a highly heterogeneous load distribution that creates special vulnerability to attacks on key nodes, Motter and Lai explained. Network nodes are the information equivalent of airline hubs, where electronic data or electrical power flows in and out in many directions.

"In a network of computers, the nodes are computers, and the load is the amount of information a node is required to transmit," Motter said. Networks exhibit homogeneity when the load is about the same in every node, he explained. Nodes in heterogeneous networks, on the other hand, have much more load than average.

In systems where some nodes are central -- for instance, backbone routers in the Internet, "eliminating those nodes is likely to cause subsequent failures and generate a cascade, while eliminating peripheral nodes will have little effect," Watts said. "In systems where all nodes have roughly the same importance -- homogeneous systems -- it doesn't matter much how you pick your targets."

The "really interesting" aspect of cascades, Watts added, "is how apparently insignificant failures can occasionally generate very large cascades.…
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