Institute for Systems Research

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Author: search.filters.author.Stathatos, K.Subject: search.filters.subject.Systems Integration Methodology

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    Adaptive Data Broadcast in Hybrid Networks
    (1997) Stathatos, K.; Roussopoulos, N.; Baras, John S.; ISR; CSHCN
    Hybrid networks combine multiple communication modes and are fast, emerging as the most viable solution for the ever increasing demand for bandwidth and data services. Taking advantage of this new technology, we are proposing a hybrid scheme which effectively combines broadcast for massive data dissemination and unicast for individual data delivery. The goal is to build highly scalable systems with small response time. In this paper, we describe a technique that continuously adapts the broadcast content to match the hot-spot of the workload. We show that the hot-spot can be accurately obtained by, monitoring the ``broadcast misses'' observed through direct requests.

    This is a major departure from all other broadcast optimization schemes which are handicapped by their total reliance on complete knowledge of both ``hits'' and ``misses''. We also show that the proposed adaptive scheme performs effectively even under very dynamic and rapidly changing workloads. Extensive simulation results demonstrate both the scalability and versatility of, the technique. Another basic result obtained in this paper is that the overall, system's throughput depends only on the size of the hot-spot and not on the volume of the workload. This has far reaching implications for very large scale and high volume wide area information systems.

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    Adaptive Data Broadcasting Using Air-Cache
    (1996) Stathatos, K.; Roussopoulos, N.; Baras, John S.; ISR; CSHCN
    In the Data AirWaves Project at University of Maryland, we are integrating Direct Broadcast Satellite (DBS) systems with terrestrial networks to provide a hybrid and effective communication substrate lying between data resources and remote/mobile user applications. Smooth integration of these two media balances the need for rapid data dissemination to very large numbers of clients and on-demand interactive data services. This paper describes the air-cache, a method for effective data broadcasting and an algorithm which rapidly adapts the content of the cache based on the ﲭisses which result in explicit (on- demand) data requests. Simulation results show that the hypothesis of adapting based only on the misses performs quite reasonably and has very little deviation from a system that has complete information - both hits and misses.
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    Integrated Network Management of Hybrid Networks
    (1996) Baras, John S.; Ball, Michael O.; Karne, Ramesh K.; Kelley, Stephen; Jang, Kap D.; Plaisant, C.; Roussopoulos, N.; Stathatos, K.; Vakhutinsky, A.; Valluri, J.; Whitefield, D.; ISR; CSHCN
    We describe our collaborative efforts towards the design and implementation of a next generation integrated network management system for hybrid networks (INMS/HN). We describe the overall software architecture of the system at its current stage of development. This network management system is specifically designed to address issues relevant for complex heterogeneous networks consisting of seamlessly interoperable terrestrial and satellite networks. Network management systems are a key element for interoperability in such networks. We describe the integration of configuration management and performance management. The next step in this integration is fault management. In particular we describe the object model, issues of the Graphical User Interface (GUI), browsing tools and performance data graphical widget displays, management information database (MIB) organization issues. Several components of the system are being commercialized by Hughes Network Systems.
      A revised version of this report has been published in
      Proceedings of the 1st Conference of Commercial Development of Space, Part One, pp. 345-350, Albuquerque, New Mexico, January 7-11, 1996.
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    Consistency and Performance of Concurrent Interactive Database Applications
    (1995) Stathatos, K.; Kelley, Stephen; Roussopoulos, N.; Baras, John S.; ISR; CSHCN
    In many modern database applications, there is an emerging need for interactive environments where users directly manipulate the contents of the database. Graphical user interfaces (GUIs) display images of the database which must reflect a consistent up-to-date state of the data with minimum perceivable delay to the user. Moreover, the possibility of several applications concurrently displaying different views of the same database increases the overall system complexity. In this paper, we show how design, performance and concurrency issues can be addressed by adapting existing database techniques. We propose the use of suitable display schemas whose instances compose active views of the database, an extended client caching scheme which is expected to yield significant performance benefits and a locking mechanism that maintains consistency between the GUIs and the database.