Institute for Systems Research
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Item Multicast Routing and Resource Allocation in a Mobile Wireless Network Like the Digital Battlefield(1997) Bhattacharya, Rupla; Ephremides, Anthony; ISR; CSHCNﲍulticasting refers to the transmission of the same information to several destinations. In this paper we are addressing the issue of multicast routing in a wireless network that consists of an arbitrarily large number of nodes, each of which is mobile in an unpredictable manner. Most existing multicast algorithms have been developed for non-wireless, stationary networks in which there is an abundance of bandwidth and where intended destinations initiate their connection to the multicast tree. In the Digital Battlefield of the future, bandwidth may be limited if not scarce and, in addition to destination-initiated connections, there will be purely source-initiated multicasts that correspond to typical command or reconnaissance messages. In this paper, we establish the beginnings of a complete multicast algorithm that is capable of adapting to topological changes. More importantly, the algorithm is combined with dynamic channel allocation procedures that are capable of reassigning bandwidth resources on an as-needed basis throughout the network. Power control is applied to tradeoff between routing delays and number of connection requests satisfied. The goal of the algorithm is to establish and maintain the maximum number of connection requests while making efficient use of available bandwidth and avoiding congestion which might lead to network collapse.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 Combating Performance Degradation in Highly Mobile Networks Using Rate Control(1997) Stamatelos, D.; Ephremides, Anthony; ISR; CSHCNWe examine a simple technique for combating performance degradation by, adjusting the rate of the received signal. Using adaptive demodulation, the receiver can respond to deteriorating conditions trading BER for rate and vice-versa, without involving the transmitter. This way the receiver has more control on the tolerated distortion. The implementation of this technique does not require modifications of the hardware of neither the transmitter nor the receiver, and its application can be very practical. The performance degradation which occurs by receiving a degraded version reliably versus receiving a non-degraded version unreliably, depends on the service and can be very subjective, making this technique very attractive for voice and video communication. This technique, independently or jointly with slow power control, can be a useful tool in network control and resource allocation.- A copy of this report has been published in the proceedings of
The 1st Annual Advanced Telecommunications/Information Distribution Research Program Conference, January 21-22, 1997.Item Routing Algorithms in All-Mobile Wireless Networks(1997) Michail, Anastassios; Ephremides, Anthony; ISR; CSHCNIn networks with mobile radio nodes in which connectivity varies, rapidly with time, it is necessary to develop algorithms for identifying, and maintaining paths between communicating pairs of nodes. Motivated by, earlier work that accomplishes such a task for data gram packet service, we develop a similar algorithm for connection-oriented service. The algorithm establishes circuit routes for initial connection based on a mechanism of short packets exchange and takes advantage of the possibility to convert a connectivity change into a ``soft'' failure to maintain and re-route on-going sessions. In this paper we give a presentation of the algorithm which is currently undergoing extensive simulation-based evaluation.- A copy of this report has been published in the proceedings of
The 1st Annual Advanced Telecommunications/Information Distribution Research Program Conference, January 21-22, 1997.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 Enhancement of Cellular Service via the Use of Satellite Capacity(1995) Ayyagari, Deepak; Ephremides, Anthony; ISR; CSHCNIn mobile communications, new services are being launched that provide extended geographical coverage of cellular service via the satellite. The additional satellite capacity can be shared among all the cells, thereby augmenting the dedicated cellular capacity available within the cells. This additional shared capacity has the inherent potential for increasing efficiency, as the extra channels can be assigned wherever they are needed rather than pre-allocating them. We considered the performance advantage the satellite offers in off-loading congestion within the cellular covered area. We propose a model for the hybrid network based on the recently proposed Multiple Service Multiple Resource concept. This model has been used in performing a detailed analysis that demonstrates the marked improvement in performance obtained by augmenting cellular capacity via the satellite and quantifies the gains achieved therein.