or devices. The new software may help assuage corporations' concerns about moving business-critical functions onto IP networks. "Ultimately, an IP network is only as good as the communication between its routers," says Guerin, who founded Ipsum with one-time IBM colleague Raju Rajan, now Ipsum's chief technology officer. "When routers share inac- curate information, it can slow or freeze a network; such performance diffi- culties are generally the first sign of trouble. But ideally you'd like to catch the problem before network performance is compromised." Because it's nearly impossible even for skilled network administrators to spot less-than-optimal communication between routers, such problems can take a significant amount of time and money to solve. Performance sometimes suffers for extended periods as computer professionals attempt to identify the UNTANGLING TANGLED NETS problem, making organizations increasingly interested in automating moni- toring of IP networks. In addition to monitoring existing networks, Route Dynamics can also predict the performance of a network. If a user wants to determine how an added piece of equipment will affect a network's performance, Route Dynamics can perform simulations. Chapter Something in the Air-Radio and Location Technologies Over the past century, radio has experienced periodic technological revolu- tions. In the 1920s, amplitude modulation (AM) voice technology began replacing spark gap telegraphy. In the 1950s, frequency modulation (FM) started its gradual yet relentless takeover of AM technology. Now digital radio, which replaces analog modulation technologies with data streams, and software-defined radios, which allow a device to be configured into any type of radio its user desires, are the next great leaps forward in radio technology. 6.1 DIGITAL RADIO Digital radio already surrounds us. Most mobile phones are already digital. And as subscribers to the XM Radio and Sirius services will readily attest, digital broadcast radio is already here (following digital te