Applications that require the communication of multiple video streams can consume considerable bandwidth and computing resources, which poses a challenge for the widespread use of videoconferencing over the IP Internet. On the one hand, the bandwidth of the link connecting a given participant to a videoconferencing session may not be enough to support many video streams at bit rates of 500 kbps or more, especially when the participant is connecting to the rest of the Internet through a wireless link. On the other hand, the processing capacity of a participating site may not be enough to decode several video streams in real time. This paper explores the use of floor control over videoconferencing applications as a means to support videoconferences with many participating sites, but with a processing and communication overhead per site that is equivalent to a two-party videoconference. The main tradeoff we explore is the scalability attained with floor control versus the latencies incurred with floor transitions, which can be much too disruptive to the videoconference participants. We present a viable compromise in which only the video stream of the "floor holder" is sent to all sites, but the floor-passing protocol is such that it supports a brief overlap of the transmissions from the old and the new floor holder, such that the participants in the videoconference can instantaneously switch over to the media streams of the next speaker in an apparently seamless transition. Experimental results and implementation in a research video-conferencing system show that the proposed protocol can run effectively, eliminating race conditions, while maintaining scalability and reliability

Broadcasting protocols for video-on-demand continuously retransmit videos that are watched simultaneously by many viewers. Nearly all broadcasting protocols assume that the client set-top box has enough storage to store between 48 and 60 minutes of video. We propose to use this storage to anticipate the customer requests and to preload, say, the first 3 minutes of the top 16 to 20 videos. This would provide instantaneous access to these videos and also eliminate the extra bandwidth required to handle compressed video signal.

Managing scientific data is a challenging task, and many of the problems it presents have yet to be adequately solved. The Real-time Environmental Information Network and Analysis System (REINAS) is an operational solution to the problem of collecting and distributing environmental data in a real-time context, as well as supporting data acquisition, retrieval, visualization and long-term data maintenance. The system is built around one or more databases and has been developed to support both real-time and retrospective regional scale environmental science. Continuous real-time data is acquired from dispersed sensors and input to a logically integrated but physically distributed system. The database engine provides a powerful structure to handle data management, but current database technology can have difficulty meeting the performance requirements that a large real-time environmental system demands. The REINAS architecture and current status is described in detail, including the challenges that were addressed in the construction of an operational system which includes a regional wireless instrumentation network comprised of over 200 instrument platforms and 1500 sensor streams producing real-time data of interest to thousands of users.

An interactive geo-data analysis and display system (GADS) has been implemented to support research on man-computer problem-solving. The focus is on problems involving data which can be related to a geographical location. The research goal is to develop systems which non-programmers can use to apply job-specific experience to the definition and solution of instructured problems. The systems must enable users to select, display, manipulate, and interpret data in a sequence which they determine during interaction. To support this requirement GADS provides a data extraction technique for accessing data stored in a variety of files, and a set of data analysis and display functions for conversational problem exploration and solution. In a case-study evaluation, police officers used GADS to solve a manpower allocation problem. The evaluation results identify user characteristics which the system must support and illustrate the value of interactive-problem solving systems.A video tape will show the architecture of the system and will illustrate its use in a manpower allocation problem.

An interactive system designed to study the spatial aspects of urban growth in Santa Clara County, San Jose, Calif., is described. The system is built around a mathematical model of urban growth and provides hands-on control of input, operation of the model, and data display.