d model one minute of such large-scale network operations in only a few minutes of clock time. Using the high-performance computers at the Pittsburgh Supercomputing Center, the Georgia Tech simulators used as many as 1,534 processors to simul- taneously work on the simulation computation, enabling them to model more than 106 million packet transmissions in one second of clock time-two to three orders of magnitude faster than simulators commonly used today. In comparison, the next closest packet-level simulations of which the research team is aware have simulated only a few million packet transmissions per second. 5.10 UNTANGLING TANGLED NETS New software developed by Ipsum Networks, a start-up cofounded by a Uni- versity of Pennsylvania engineering professor, shows promise in detecting hard-to-spot bottlenecks in computer networks. The first version of this soft- ware, known as Route Dynamics, is available to companies and other users that transmit data via decentralized IP networks. "IP networks have gained popularity because they don't rely on a central computer and are therefore more resistant to attacks and failure, but this complex architecture also makes them much harder to monitor and repair," says Roch Guerin, professor of electrical and systems engineering at Penn and CEO of Ipsum. "Managing an IP network is now a labor-intensive art rather than an automated science. Making matters worse, corporations can lose lit- erally millions of dollars for every second their IP network is down." IP networks work by dividing data into packets, which are addressed and then transmitted by way of a series of routers. A router detects a packet's ulti- mate address and communicates with other routers before sending the packet to another machine that it believes is closer to the packet's final destination. Route Dynamics monitors communications between routers as well as com- munications between entire networks, a level of surveillance not attainable with existing programs, which measure only network speed or simply monit