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Under funding from the Defense Advanced Research Projects Ageiy (DARPA) for joint military and law enforcement technologies, demonstrations of secure information transfer in support ci law enforcement and military operations other than war, using wireless and wired technology, were held in September 1996 at several locations in the United States. In this paper, the network architecture, protocols, and equipment supporting the demonstration's scenarios are presented, together with initial results, including lessons learned and desired system enhancements.Wireless networks ci opportunity encompassed inbuilding (wireless-LAN), campus-wide (Metricom Inc.), metropolitan (AMPS cellular, DPD),* and national (one-and twoway satellite) systems. Evolving DARPA-sponsored packet radio technology was incorporated. All data was encrypted, using Multilevel Information System Security Initiative (MIsSr) FORTEZZA technology, for carriage over unsecured and unclassified commercial networks. The identification and authentication process inherent in the security system permitted logging for database sccesses and provided an audit trail useful in evidence gathering. Wireless and wireline communications support, to and between modeled crisis management centers, was &monstrated. Mechanisms for the guarded transport o data through the Secret-high military tactical Internet were included, to supportjoint law enforcement and crisis management missions.A secure World Wide Web (WWW) browser forms the primary, user-friendly interface for information retrieval and submission. The WWW pages were stnictured to be sensitive to the bandwidth, error rate, and cost o the communications medium in use (e.g., the use ol and resolution for graphical data). Both still and motion compressed video were demonstrated, along with secure voice transmission from laptop computers in the field. Issues ci network bandwidth, airtime costs, and deployment status are discussed.

Information on other‐user interference is important in predicting the performance of high frequency (HF) systems. For many systems, especially frequency‐hopping systems, other‐user interference frequently is more important than man‐made noise from incidental radiators (for example, power lines) or atmospheric noise from lightning. Occupancy of individual channels and congestion of allocated HF bands (for example, fixed and mobile, amateur) vary with type of service, frequency, time of day, season, angle of arrival, type of receiving antenna, bandwidth, threshold, geographic location, and sunspot number. This paper summarizes channel occupancy and band congestion observations made in the continental United States and Europe in 1987 with SRI International's Mobile Spectrum Monitoring Unit. The data on band congestion are compared with the empirical model developed by researchers at the University of Manchester Institute for Science and Technology (UMIST), Manchester, United Kingdom. A concept for extending the UMIST model for congestion at a point to a model for congestion within a region is described.