Institute for Systems Research
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Item Fair Bandwidth Allocation and Buffer Management in Hybrid Network Gateways(2000) Srinivasan, Roshni; Vaidyanathan, Ravichander; Baras, John S.; Baras, John S.; ISR; CSHCNIn this paper, we present an efficient and fair resource allocationscheme for scheduling and buffer management in a bottleneck hybridsatellite-terrestrial network gateway with per-flow TCP queues.Ourfirst contribution is the use of Fair Queueing in conjunction withProbabilistic Fair Drop, a new buffer management policy to allocatebandwidth and buffer space in the gateway, to ensure that all TCPflows threading the gateway achieve high end-to-end throughput andfair service.
Our second contribution is to introduce the concept ofbuffer dimensioning to alleviate the inherent bias of the TCPalgorithm towards connections with large Round Trip Time.
In supportof each of these contributions, we report on extensive simulationresults. Our scheme outperforms other resource allocation schemesreported in the literature and in particular, demonstrates significantimprovements in fairness to long RTT connections in the hybrid networkframework.
Item Window Distribution of Multiple TCPs with Random Loss Queues(1999) Misra, Archan; Baras, John S.; Ott, Teunis; Baras, John S.; ISR; CSHCNIn this paper, we consider the case of multiple ideal and persistent TCP flows (flows that are assumed to be performing idealized congestion avoidance) interacting with queue management algorithms that perform random drop-based buffer management. Our objective is to determine the stationary congestion window distribution of each of the TCP flows whenthe router port implements algorithms like RED (Random Early Detection)or ERD (Early Random Drop).We first present an analyticaltechnique to obtain the 'mean' queue occupancy and the 'mean' of the individual TCP windows. Armed with this estimate of the means, wethen derive the window distribution of each individual TCPconnection. Extensive simulation experiments indicate that, under a wide variety of operating conditions, our analytical method is quite accurate in predicting the 'mean' as well asthe distributions. The derivation of the individual distributions is based upon a numerical analysis presented which considers the case of a single TCP flow subject to variable state-dependent packet loss.
Item Estimation of Hidden Markov Models for Partially Observed Risk Sensitive Control Problems(1997) Frankpitt, Bernard A.; Baras, John S.; ISRWe look at the problem of estimation for partially observed, risk-sensitive control problems with finite state, input and output sets, and receding horizon. We describe architectures for risk sensitive controllers, and estimation, and we state conditions under which both the estimated model converges to the true model, and the control policy will converge to the optimal risk sensitive policy.Item Hybrid Internet Access(1995) Arora, Vivek; Baras, John S.; Dillon, Douglas; Falk, Aaron D.; Suphasindhu, Narin; ISR; CSHCNAccess to the Internet is either too slow (dial-up SLIP) or too expensive (switched 56 kbps, frame relay) for the home user or small enterprise. The Center for Satellite and Hybrid Communication Networks and Hughes Network Systems have collaborated using systems integration principles to develop a prototype of a low-cost hybrid (dialup and satellite) network terminal which can deliver data from the Internet to the user at rates up to 160 kbps. An asymmetric TCP/IP connection is used breaking the network link into two physical channels: a terrestrial dial-up for carrying data from the terminal into the Internet and a receive-only satellite link carrying IP packets from the Internet to the user. With a goal of supporting bandwidth hungry Internet applications such as Mosaic Gopher, and FTP, this system has been designed to support an Intel 80386/486 PC, any commercial TCP/IP package, any unmodified host on the Internet, and any of the routers, etc., within the Internet.. The design exploits the following three observations: 1) satellites are able to offer high bandwidth connections to large geographical area, 2) a receiver-only VSAT is cheap to manufacture and easier to install than one which can also transmit, and 3) most computer users, especially those in a home environment, will want to consume much more information than they generate. IP encapsulation, or tunneling, issued to manipulate the TCP/IP protocols to route packets asymmetrically.Item Hybrid Network Architectures; A Framework for Comparative Analysis(1995) Baras, John S.; Campanella, S. Joseph; Kirkwood, Timothy J.; ISR; CSHCNThe Global Information Infrastructure of the future will include a great variety of heterogeneous, seamlessly interconnected networks. There are strong variety of heterogeneous, seamlessly interconnected networks. There are strong technical and economic reasons predicating the emergence of these hybrid networks which will include many diverse terrestrial (tethered or wireless) and satellite networks in an interoperating configuration. This paper critically analyzes the basis for these new architectures and examines the various possibilities that will emerge in various phases in the future. A summary view is presented for these emerging hybrid architectures, the alternative components and subsystems available and the trade-offs that must be considered. The role of satellites is carefully analyzed and several conclusions are drawn. This paper will present a summary of the work and views of the Center for Satellite and Hybrid Communication Networks todate, in this important area. Specific design and performance evaluation tools being developed will also be described.Item A Dynamic Routing Algorithm in Mixed Media Networks with Integrated Voice and Data Traffic(1993) Chen, Shih-Wei; Baras, John S.; ISR; CSHCNIn this paper, we consider mixed media networks with multi-media traffic to find the optimal splitting ratio between satellite network and terrestrial network for data and voice traffic dynamically. We constantly monitor the traffic and measure the arrival rate and occupancy of every link. Based on these data, we optimize data traffic delay in a suitable time-frame under the constraints of voice traffic blocking probabilities of voice transmission links being less than specified value, which is up to system's design or users' requirements. A dynamic routing algorithm is presented.