Institute for Systems Research Technical Reports

Permanent URI for this collectionhttp://hdl.handle.net/1903/4376

This archive contains a collection of reports generated by the faculty and students of the Institute for Systems Research (ISR), a permanent, interdisciplinary research unit in the A. James Clark School of Engineering at the University of Maryland. ISR-based projects are conducted through partnerships with industry and government, bringing together faculty and students from multiple academic departments and colleges across the university.

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Subject: search.filters.subject.performance

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    A performance comparison between two consensus-based distributed optimization algorithms
    (2012-05-04) Matei, Ion; Baras, John
    In this paper we address the problem of multi-agent optimization for convex functions expressible as sums of convex functions. Each agent has access to only one function in the sum and can use only local information to update its current estimate of the optimal solution. We consider two consensus-based iterative algorithms, based on a combination between a consensus step and a subgradient decent update. The main difference between the two algorithms is the order in which the consensus-step and the subgradient descent update are performed. We show that updating first the current estimate in the direction of a subgradient and then executing the consensus step ensures better performance than executing the steps in reversed order. In support of our analytical results, we give some numerical simulations of the algorithms as well.
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    Improving TCP Performance over High-Bandwidth Geostationary Satellite Links
    (1999) Bharadwaj, Vijay G.; Baras, John S.; ISR; CSHCN
    The Transmission Control Protocol (TCP) is the most widely used transportprotocol in the Internet today. The problem of poor TCP performance oversatellite networks has recently received much attention, and much work hasbeen done in characterizing the behavior of TCP and proposing methods forimprovement. Meanwhile it remains hard to upgrade the majority of legacyhost and gateway systems in the Internet that are running old and outdatedsoftware so that they can perform better in the changing networks of today.

    In this thesis we consider an alternative network architecture, where largeheterogeneous networks are built from small homogeneous networksinterconnected by carefully designed proxy systems. We describe the designand implementation of such a proxy and demonstrate marked performanceimprovements over both actual and simulated satellite channels. We alsodiscuss some benefits and drawbacks of using proxies in networks andexplore some tradeoffs in proxy design.

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    Internet Service via Broadband Satellite Networks
    (1999) Bharadwaj, Vijay G.; Baras, John S.; Butts, Norman P.; Baras, John S.; ISR; CSHCN
    The demand for Internet bandwidth has grown rapidly in the past few years. A new generation of broadband satellite constellations promises to provide high speed Internet connectivity to areas not served by optical fiber, cable or other high speed terrestrial connections. However, using satellitelinks to supply high bandwidth has been difficult due to problems with inefficient performance of the Internet's TCP/IP protocol suite over satellite. We describe an architecture for improving the performance of TCP/IP protocols over heterogeneous network environments, especially networks containing satellite links. The end-to-end connection is split into segments, and the protocol on the satellite segment is optimized for the satellite link characteristics. TCP congestion control mechanisms are maintained on each segment, with some coupling between the segments to produce the effect of end-to-end TCP flow control. We have implemented this design and present results showing that using such gateways can improve throughput for individual connections by a large factor over paths containing a satellite link.

    The research and scientific content in this material has been published in the Proceedings of the SPIE, vol. 3528, February 1999, 169-180.