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28/7/2008, J. Baras, "Trust and Reputation in Communication, Social and Other Network"

                    A general abstract of the talk:
                 
Trust and reputation are critical concepts in networks – communication, control, computer, social, web-based, economic, biological. Trust evaluation leads to the development of relations and collaborations. These evaluations are based either on direct ‘communal’ monitoring and inference by the nodes, or on indirect references and credentials. We describe a  new fundamental ways for analyzing and evaluating trust in autonomic networks. Due to the dynamic and changing nature of autonomic networks trust evidence and the resulting evaluations may be uncertain and incomplete. The indirect evaluation process is modeled as a path problem on a directed graph, where nodes represent entities, and edges represent trust relations. We develop a novel formulation of trust computation as ‘linear’ iterations on ordered semirings. Using the theory of semirings, we analyze several key problems on the performance of trust algorithms. The direct trust evaluation process is modeled as iterated games on dynamic graphs. We present several explicit examples. We also present results on trust dynamics and propagation, including connections with statistical mechanics of spin glasses and consensus problems. We conclude with new fundamental principles for ‘Network Science’ bringing together algebraic, optimization and game theoretic methods. We conclude with future directions and open problems.  

Short bio:

B.S. in Electrical Eng. from the Nat. Techn. Univ. of Athens, Greece, 1970; M.S. and Ph.D. in Applied Math. from Harvard Univ. 1971, 1973. Since 1973 with the Electrical and Computer Engineering Department, and the Applied Mathematics Faculty, at the University of Maryland College Park. Faculty member in the Department of Computer Science and Fischell Department of Bioengineering. He was the founding Director of the Institute for Systems Research (ISR) from 1985 to 1991.  Since 1991, has been the Director of the Maryland Center for Hybrid Networks (HYNET). Fellow of the IEEE and a Foreign Member of the Royal Swedish Academy of Engineering Sciences. Received the 1980 George Axelby Prize from the IEEE Control Systems Society and the 2006 Leonard Abraham Prize from the IEEE Communications Society. Professor Baras' research interests include control, communication and computing systems.
  
 

20/5/2008, R. Cascella, "Security issues in autonomic systems: the "value" of reputation".

                     A general abstract of the talk:

In this talk we will provide some basic definitions for an autonomic system, we will discuss security issues that might arise in that might arise in this new communication paradigm, and we will focus mainly on trust and reputation approaches to thwart selfish behaviour. In this talk we discuss the importance for a node to build and use its reputation value and we present a game-theoretical framework, based on the generalized form of Iterated Prisoner's Dilemma, to model the interactions of rational and selfish nodes in distributed systems. We study how a node takes into account the change of its reputation when deciding its behaviour in a transaction and discuss the Nash Equilibrium in the system. We finally present simulation results on nodes' interactions under different strategies to show how cooperation and reputation evolve in the system.

20/5/2008, P. Michiardi, "On the Impact of Greedy Strategies in BitTorrent Networks: the Case of BitTyrant".

                    A general abstract of the talk:

The success of BitTorrent has fostered the development of variants to its basic components. Some of the variants adopt greedy approaches aiming at exploiting the intrinsic altruism of the original version of BitTorrent in order to maximize the benefit of participating to a torrent.

In this work we study BitTyrant, a recently proposed strategic client. BitTyrant tries to determine the exact amount of contribution necessary to maximize its download rate by dynamically adapting and shaping the upload rate allocated to its neighbors. We evaluate in detail the various mechanisms used by BitTyrant to identify their contribution to the performance of the client.

Our findings indicate that the performance gain is due to the increased number of connections established by a BitTyrant client, rather than for its subtle uplink allocation algorithm; surpisingly, BitTyrant reveals to be altruistic and particularly efficient in disseminating the content, especially during the initial phase of the distribution process. The apparent gain of a single BitTyrant client, however, disappears in the case of a widespread adoption: our results indicate a severe loss of efficiency that we analyzed in detail.

10/1/2008, J. Antoniou, "Always Best Connectivity in 4th Generation Heterogeneous Networks".

A general abstract of the talk:

Future Communication Networks are envisioned to be based upon a common, flexible and scalable convergence platform, where different access networks, different terminals and different services can coexist. The new user capabilities spawn a demand for Always Best Connectivity (ABC), i.e. that a user can always have the best possible connection regardless of place and time. This brings forth a new communication paradigm, which is user-centric, i.e. the user is no longer bound to only one access network but can choose the best available access network to satisfy a specific service request. We consider the selection of access network, specifically for multicast/broadcast users and propose a scheme implemented using IMS signalling.

20/12/2007, Gr. Karagiorgos, " Local Iterative Schemes: Load Balancing and Random Walks".

25/10/2007, E. Jaho, "Distributed Selfish Replication under Node Churn". [PPT]

23/10/2007, G. Pollatos, "The Dominating Set Problem". [PPT]

L. Tzevelekas, "Directed Budget-Based Clustering for WSN". [PPT]

L. Tzevelekas, "Random Walks in WSNs". [PPT]

12/2005, L. Tzevelekas, "Routing in WSNs through analogies with electrostatics". [PPT]