in a less ad hoc, more comprehensive fashion. Research on modeling the behavior of software systems composed from heterogeneous parts, for example, fits this category.
NETWORKING: THE NEED FOR ADAPTIVITY
Because of inherently unpredictable conditions, the communications support needed in a crisis must be adaptable; the steering committee characterizes the required capability as "adaptivity." Adaptivity involves making the best use of the available network capacity (including setting priorities for traffic according to needs and blocking out lower-priority traffic), as well as adding capacity by deploying and integrating new facilities. It also must support different kinds of services with fundamentally different technical demands, and to do so efficiently requires adaptivity. This section addresses specific areas for research in adaptive networks and describes the implications of a requirement for adaptivity; the importance of adaptivity at levels of information infrastructure above the network is discussed in other sections of this chapter.
Box 2.1 provides a sampling of networking research priorities discussed in the workshops. Although problems of networking that arise in national-scale applications are not entirely new, they require rethinking and redefinition because the boundaries of the problem domains are changing. Three issues that influence the scope of networking research problems are (1) scale, (2) interoperability, and (3) usability.
Scale. High-performance networking is often thought of in terms of speed and bandwidth. Speed is limited, of course, by the speed of light in the transmission medium (copper, fiber, or air), and individual data bits cannot move over networks any faster. However, the overall speed of networks can be increased by raising the bandwidth (making the pipes wider and/or using more pipes in parallel) and reducing delays at bottlenecks in the network. High-speed networks (which include both high-bandwidth conduits or "pipes" and high-speed switching and routing) allow larger streams of data to traverse the network from point A to point B in a given amount of time. This makes possible the transmission of longer individual messages such as data files, wider signals (such as full-motion video), and greater numbers of messages (such as data integrated from large numbers of distributed sensors) over a given path at the same time. Research challenges related to the operation of high-speed networks include high-speed switching, buffering, error control, and similar needs; these were investigated with significant progress in the Defense Advanced Research Project Agency's (DARPA's) gigabit network testbeds.
- Speed and bandwidth are not the only performance challenges related to scale; national-scale applications must also scale in size. The number of information sources involved in applications may meet or even far exceed the size of the