| Speaker: | Dr. Leandros Tassiulas, University of Thessaly |
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| Abstract: | Unpredictability in traffic load variations, link capacity fluctuations, topology modifications, node failures or other types of intentional misbehavior may lead the network in overload conditions. Instantaneous system response in those stressful situations is essential for effective crisis management in the system. In this talk we study the operation of the network in overload. The notion of superflow is introduced as a generalization of flow where flow conservation at the nodes need not necessarily hold. Superflows facilitate accurate modeling of overload situations where the traffic generation intensity may temporarily exceed the capacity at different localities of the network. We propose as a measure for overload response the vector of backlog build up at the various network nodes when the network changes operational mode to overload. Optimization of that measure has as an effect most balanced allocation of the overload to the different network nodes. In that manner for instance the time to buffer overflow is maximized. We show that in the space of overload vectors there is one that is lexicographically minimal, thus most balanced and we characterize it. Furthermore we show that that vector is the unique solution for a wide class of optimization problems with objective function that is the sum of nondecreasing functions of the node overloads. Furthermore we characterize the class of most balanced superflows as those achieving most balanced overflow vectors. The characterization of most balanced superflows reveals certain structural properties of the network and helps to identify regions that experience the maximum stress from the current distribution of traffic intensity irrespectively of what the routing policy might be. Finally we show how to achieve most balanced overflow through a simple distributed algorithm. Joint work with L. Georgiadis |
| Biography: | Leandros Tassiulas is Professor in the Dept of Computer Engineering and Telecommunications at the University of Thessaly Greece since 2002 and Research Professor at the University of Maryland College Park. His research activity over the last fifteen years is towards the development of communication and information processing networks that facilitate access and exchange of information among multiple entities. Current research and teaching topics include wireless mobile communications, ad-hoc networks, smart antennas, sensor networks, high speed networked environments. He was Assistant Professor at Polytechnic University, NY, 1991-1995, Associate Prof. at the University of Maryland, College Park until 2002 (on leave 2000-2002) and Professor of Computer Science at the University of Ioannina Greece 1999-2002. He obtained the Diploma in Electrical Engineering from the University of Thessaloniki, Greece in 1987, and the M.S. and Ph.D. degrees in Electrical Engineering from the University of Maryland, College Park in 1989 and 1991 respectively. He has been Associate Editor for Communication Networks for IEEE Transactions on Information Theory and an editor for IEEE/ACM Transactions on Networking. His received a National Science Foundation (NSF) Research Initiation Award in 1992, an NSF CAREER Award in 1995, the Office of Naval Research Young Investigator Award in 1997 and the INFOCOM `94 best paper award. In 1999, he was awarded the "Bodossaki Foundation Academic Prize" in the field: Applied Science: Theories, Technologies and Applications of Parallel and Distributed Computing Systems. He represent Greece in the 6th framework program of the European Union, as national expert in telecommunications. |
| Presented On: | Friday, March 11, 2005 |
| Videotape: | Click to View the Streaming Quicktime Presentation This presentation requires the free Apple QuickTime Player which can be downloaded from the following link: www.apple.com/quicktime/download |
