Institute for Systems Research
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Item A Scheme to Improve Throughput for ARQ-Protected Satellite Communication(1997) Friedman, Daniel E.; Ephremides, Anthony; ISR; CSHCNAutomatic-repeat-request (ARQ) error control is often employed to assure high fidelity information transmission. However, ARQ error control can provide poor throughput for satellite multicasting. The throughput in such communication may be improved by the combination of a terrestrial network parallel to the satellite network and a judiciously modified ARQ protocol. In particular, retransmitted ARQ frames can be sent terrestrially in such a hybrid network, allowing higher throughput than in a pure- satellite network. This work presents analytic results to establish the potential for improving the throughput of satellite multicast communication employing ARQ error control by the adoption of such a hybrid network architecture.Item The Acts Experiments program at the Center for Satellite and Hybrid Communication Networks(1997) Friedman, Daniel E.; Gupta, Sonjai K.; Zhang, C.; Ephremides, Anthony; ISR; CSHCNThis paper describes experiments conducted over ACTS and the associated T1~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. 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. 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 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 Error Control for Satellite and Hybrid Communication Networks(1995) Friedman, Daniel E.; Ephremides, A.; ISR; CSHCNBoth forward-error correction (FEC) and automatic-repeat-request (ARQ) error control schemes are used for assuring the accuracy of information transferred through imperfect channels. In satellite systems in which propagation times are typically large, ARQ error control can result in poor throughput to the destination. Also, an ARQ protocol for satellite multicast communication must be carefully crafted to assure good throughput to all destinations regardless of which stations require retransmissions.Supplementing a satellite link with a parallel terrestrial link may allow mitigating some problems of using ARQ in satellite communication systems. ARQ acknowledgments, and possibly retransmissions as well, can be sent terrestrially in such a hybrid network, and so avoid the large satellite propagation delay. The satellite transmission capability of a receiving station which communicates with the transmitter exclusively by terrestrial means can be eliminated and the system cost correspondingly reduced. Further, multicasting with a hybrid network may allow retransmissions to be conducted without interrupting the flow of new information to all destinations, so throughput need not drastically suffer if retransmissions are required.
The degree to which throughput can be improved by adopting a hybrid network is not clear. A hybrid network's effect on the fidelity of information delivered to the destination(s) is also not clear. An experiment is presented for investigating such error control issues of hybrid networking.