Browsing by Author "Wenke Lee, Member"

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    Performance Evaluation of TEAR, a TCP-friendly Flow Control Protocol, Over the Internet and Wireless Networks
    (2001-07-26) Jayaram, Ranjith S.; Injong Rhee, Chair; George N. Rouskas, Member; Wenke Lee, Member
    TCP Emulation at Receivers (TEAR) is a TCP-friendly protocol that has been proposed for real-time multimedia flow control. Most best-effort traffic on the Internet is well-served by TCP, the dominant transport protocol. However, many applications with real-time constraints, such as multimedia streaming find TCP's response to congestion quite severe and too drastic to deliver acceptable end-user quality. TEAR was designed in order to provide smoothly varying rate changes for such applications while being friendly to competing TCP flows. In this thesis, weevaluate and verify TEAR's performance over the Internet. We verify TEAR's fairness to TCP, the smoothness of its rate fluctuations and its stability in the presence of network perturbations. We then adapt TEAR to run over wireless networks and consider using round-trip delay instead of packet loss as a congestion indication for wireless networks. We present the results of our experiments with TEAR over commercially deployed wireless networks in South Korea. We recount our experiences with the loss-delay characteristics of these networks. We analyze how TEAR competes with TCP, which is known to suffer from severe degradations in environments where the underlying network is unreliable. We then study TEAR's rate variations and the increased longer-term predictability it provides over wireless networks. Finally, we compare the performance of a reliable protocol we built over TEAR with TCP.
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    Virtual Topology Design for Traffic Grooming in WDM Networks
    (2001-08-06) Dutta, Rudra; George N. Rouskas, Chair; Harry G. Perros, Member; Carla D. Savage, Member; Wenke Lee, Member
    Wavelength division multiplexing (WDM) in optical fiber networks iswidely viewed as the technology with the potential to satisfy theever-increasing bandwidth needs of network users effectively and on asustained basis.In WDM networks, nodes are equipped with optical cross-connects(OXCs), devices which can optically switch a signal on any givenwavelength from any input port to any output port.This makes it possible to establish light paths between any pair of network nodes.A lightpath is a clear channel in which the signal remainsin optical form throughout the physical path between the two endnodes.The set of lightpaths established over the fiberlinks defines a .Consequently, the problem arises of designing virtual topologies tooptimize a performance measure of interest for a set of trafficdemands. With the deployment of commercial WDM systems, it has become apparentthat the cost of network components, especially line terminatingequipment (LTE) is the dominant cost in building optical networks, andis a more meaningful metric to optimize than, say, the number ofwavelengths.Furthermore, since the data rates at which each individual wavelengthoperates continue to increase (to OC-192 and beyond), it becomes clearthat a number of independent traffic components must be multiplexed inorder to efficiently utilize the wavelength capacity.These observations give rise to the concept of, which refers to the techniques used to combine lower speed componentsonto available wavelengths in order to meet network design goals suchas cost minimization. Traffic grooming is a hard problem in generalwhich remains computationally intractable even for simple networks. We consider the problem of traffic grooming in ring, star andtree topologies. We provide theoretical results regarding achievabilitybounds for these networks as well as practical frameworks to obtainincreasingly better feasible solutions with the expenditure of morecomputational power.