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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Item Negotiating Access Control Policies Between Autonomous Domains(2002) Bharadwaj, Vijay G.; Baras, John S.; Baras, John S.; ISR; CSHCNAutonomous policy domains often need to share resources to accomplish a common task. To do this they must negotiate a common access control policy to the shared resources. We use mathematical techniques from game theory to show that the outcome of such negotiations can often be predicted from the distribution of power among the participants, independent of the actual mechanics of negotiation. We discuss the axiomatic derivation of some game theoretic solution concepts, and illustrate our techniques with examples.Item Improving TCP Performance over High-Bandwidth Geostationary Satellite Links(1999) Bharadwaj, Vijay G.; Baras, John S.; ISR; CSHCNThe 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.
Item Internet Service via Broadband Satellite Networks(1999) Bharadwaj, Vijay G.; Baras, John S.; Butts, Norman P.; Baras, John S.; ISR; CSHCNThe 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. Item An Architecture for Internet Service via Broadband Satellite Networks(1999) Bharadwaj, Vijay G.; Baras, John S.; Butts, Norman P.; Baras, John S.; ISR; CSHCNHigh bandwidth satellites hold out the promise of a rapidly deployablecommunications infrastructure with a natural support for mobility. However,the Transmission Control Protocol (TCP), widely used in the Internet, performspoorly over satellite links, and this presents an obstacle to thedeployment of such systems. We present an architecture that overcomesthese problems and provides an approach to building complex heterogeneousnetworks from simple units. We also present some results from our initialimplementation, which uses TCP connection splitting to improve TCPperformance over satellite links.Item Extensions of DBS and Hybrid Internet(1997) Karir, Manish; Bharadwaj, Vijay G.; Holleman, Keith; Suphasindhu, Narin; Papademetriou, Spyro; Baras, John S.; ISR; CSHCNThere has been a large amount of research dedicated to extending the asymmetric networks provided by receive-only Direct Broadcast Satellite systems like Hughes Network Systems' DirecPC product. One way to further develop Direct Broadcast Satellite services and to offset the high initial cost of these systems is to implement techniques that will allow one satellite receiver to act as a gateway for many clients to receive information. This would also help broaden the range of services provided by DBS systems. Besides providing direct-to-home traffic, DBS can be used to distribute bulk traffic to the local-loop distributors (direct-to-curb). We describe some experiments which extend the DBS system, in particular, the DirecPC and DirecTV DBS, by using the PC with the satellite receiver as a gateway to connect networks together. We also discuss simple methods of receiving multimedia traffic from the multicast backbone (MBONE) [Cas94] over the satellite link, and distributing it, through this gateway, to end users.The research and scientific content in this material will be presented at the 2nd ACM International Workshop on Satellite-Based Information Services (WOSBIS), October 1, 1997, Budapest, Hungary.