The Programmable Network Prototyping System (PNPS), which is a rapid-prototyping tool used for emulating a wide variety of communication networks, is discussed. There are two parts to the PNPS hardware: the reusable hardware modules and the control and observation system. The reusable hardware modules consist of a channel emulator and a collection of node emulators. The channel emulator can be programmed to behave like a variety of network topologies, and each node emulator is configured to behave like a node on a network under study. The control and observation system links these modules together for configuration, experimentation, and monitoring purposes. There are three phases to using PNPS. first, the various components of a proposed network are designed. Next, the components are combined and run on the hardware while its behavior is monitored. Finally, the monitoring data is analyzed in order to evaluate the network design. A menu-driven user interface guides the user through the various tools of the system.>

Parallel communication algorithms and networks are central to large-scale parallel computing and, also, data communications. This paper identifies adverse source-destination traffic patterns and proposes a scheme for obtaining relief by means of randomized routing of packets on simple extensions of the well-known omega networks. Valiant and Aleliunas have demonstrated randomized algorithms, for a certain context which we call nonrenewal, that complete the communication task in time O (log N ) with overwhelming probability, where N is the number of sources and destinations. Our scheme has advantages because it uses switches of fixed degree, requires no scheduling, and, for the nonrenewal context, is as good in proven performance. The main advantage of our scheme comes when we consider the renewal context in which packets are generated at the sources continually and asynchronously. Our algorithm extends naturally from the nonrenewal context. In the analysis in the renewal context we, first, explicitly identify the maximum traffic intensities in the internal links of the extended omega networks over all source-destination traffic specifications that satisfy loose bounds. Second, the benefits of randomization on the stability of the network are identified. Third, exact results, for certain restricted models for sources and transmission, and approximate analytic results, for quite general models, are derived for the mean delays. These results show that, in the stable regime, the maximum mean time from source to destination is asymptotically proportional to log N . Numerical results are presented.