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 Asymmetric Internet Access over Satellite-Terrestrial Networks(1996) Arora, Vivek; Suphasindhu, N.; Baras, John S.; Dillon, Douglas; ISR; CSHCNDirecPCtm's Turbo Internet is a low-cost hybrid (satellite- terrestrial) high-speed digital transmission system developed as a collaborative effort between the Center for Satellite and Hybrid Communication Networks and Hughes Network Systems. The system uses receive-only satellite links for downstream data delivery and public telephone networks at the modem speeds to provide the upstream communications path. One of the services provided is high speed Internet access based on an asymmetric TCP/IP protocol. Our principle object is to lower cost and efficiently provide high bandwidth access to Internet services such as file transfer, the World Wide Web, and the MBONE. In the initial protocol implementation, we achieved four times higher throughput than that of Today's high-speed modems (28.8 Kbps) alone2. This throughput can be further enhanced. The mismatch in bandwidth and delay in this hybrid network prevents the full use of the satellite link bandwidth (1 Mbps). This paper presents two techniques, TCP spoofing and selective acknowledgement dropping, which significantly increase the overall throughput of the hybrid network. Our approach does not require any modification to the TCP/IP protocol stacks on the end hosts. The solutions proposed in this paper could be used to improve TCP/IP performance of other hybrid networks which have the disadvantage of high bandwidth-delay products and/or low bandwidth return paths. Furthermore, we are investigating how to extend IP multicast services to such hybrid networks. The broadcast nature of Satellite communication makes it an efficient way for high- bandwidth multicast transmission.- A revised version of this technical report has been published in
Proceedings of the AIAA: 16th International Communications Satellite Systems Conference and Exhibit, Part 1, pp. 476-482, Washington, D.C., February 25-29, 1996.Item Experiments in Hybrid Networking with the Advanced Communications Technology Satellite(1996) Friedman, Daniel E.; Gupta, Sonjai K.; Zhang, C.; Ephremides, Anthony; ISR; CSHCNThis paper describes experiments conducted over ACTS that were motivated by the commercial potential of low-cost receive-only satellite terminals operating in a hybrid network environment. The first experiment tested highly adaptive methods of satellite bandwidth allocation in an integrated voice-data service environment. The second involved comparison of FEC and ARQ methods of error control for satellite communication with emphasis on the advantage that a hybrid architecture provides especially in the case of multicasts. Finally, the third experiment demonstrated hybrid access to databases through the use of Mosaic and compared the performance of internetworking protocols for interconnecting LANs via satellite.Item Review of the VSAT ACTS Experiments at the Center for Satellite & Hybrid Communication Networks(1996) Friedman, Daniel E.; Gupta, Sonjai K.; Zhang, C.; Ephremides, Anthony; ISR; CSHCNThis paper describes experiments conducted over ACTS and the associated TI VSAT terminal. The experiments were motivated by the commercial potential of low-cost receive-only satellite terminals that can operate in a hybrid network environment, and by the desire to demonstrate frame relay technology over satellite networks. A custom unit termed Frame Relay Access Switch (FRACS) was developed by COMSAT Laboratories for these experiments; the preparation and conduct of these experiments involved a total of twenty people from the University of Maryland, the University of Colorado, and COMSAT Laboratories, from late 1992 through 1995.Item Effective Extensions of Internet in Hybrid Satellite-Terrestrial Networks(1996) Arora, Vivek; Suphasindhu, N.; Baras, John S.; Dillon, Douglas; ISR; CSHCNDirect PCTM's Turbo Internet is a low-cost hybrid (satellite- terrestrial) high-speed digital transmission system developed as a collaborative effort between the Center for Satellite and Hybrid Communication Networks and Hughes Network Systems. The system uses receive-only VSAT satellite links for downstream data delivery and public telephone networks at modem speeds to provide the upstream communications path. One of the services provided is high speed Internet access based on an asymmetric TCP/IP protocol. In the initial protocol implementation, we achieved four times higher throughput than that of today high-speed modems (28.8 Kbps) alone (Falk 1995). This throughput can be further enhanced. The mismatch in bandwidth and delay in this hybrid network prevents the full use of the satellite link bandwidth (1 Mbps). This paper presents two techniques. TCP spoofing and selective acknowledgement dropping, which significantly increase the overall throughput of the hybrid network. Our approach does not require any modification to the TCP/IP protocol stacks on the end hosts. The solutions proposed in this paper could be used to improve TCP/IP performance of other hybrid networks which have the disadvantage of high bandwidth-delay products and/or low bandwidth return paths.- A revised version of this report has been published in
Proceedings of the 1st Conference of Commercial Development of Space, Part One, pp. 339-344, Albuquerque, New Mexico, January 7-11, 1996.