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We present some of the research activities of Computer Science Department on P2P systems. In particular, we discuss the following topics: Compressive Sensing in P2P systems. In this part of the talk we discuss the following problem: how to provide each peer local access to the full information (not just a summary) that is distributed over all edges of an overlay network? How can this be done if local access is performed at a given rate? We focus on large and sparse information and we propose to exploit the compressive sensing (CS) theory to efficiently collect and pro-actively disseminate this information across a large overlay network. We devise an approach based on random walks (RW) to spread CS random combinations to participants in a random peer-to peer (P2P) overlay network. CS allows the peer to compress the RW payload in a distributed fashion: given a constraint on the RW size, e.g., the maximum UDP packet payload size, this amounts to being able to distribute larger information and to guarantee that a large fraction of the global information is obtained by each peer. We analyze the performance of the proposed method by means of a simple (yet accurate) analytical model describing the structure of the so called CS sensing matrix in presence of peer dynamics and communication link failures. Our analysis reveals that the method we propose is feasible, accurate and robust to peer and information dynamics. We also argue that centralized and other distributed approaches, i.e., flooding and gossiping, are unfit in the context we consider. P2P systems: network awareness/un-awareness. Recent measurement studies have shown that traffic generated by peer-to-peer dominates the bandwidth consumption on Internet access links. The prevailing use of P2P applications (file sharing and non-file sharing) carries with it significant implications for ISPs. In 2007 (IFIP Performance) we proposed a modeling framework to study the possible strategies that a ISP can use to manage P2P file sharing traffic. Recently we are addressing the ISP behavior and their cooperative/non-cooperative attitudes. In particular, we propose a game theoretic framework to help the design of techniques promoting the ISP cooperation in P2P streaming platforms. Our investigations can be helpful for designing strategies to incentivize the ISP cooperation aiming at the minimization of inter-ISP traffic and help to provide reliable P2P streaming service. Application level coding for P2P systems. In the talk we present our results on content dissemination exploiting the digital fountain concept through the use of rateless codes. We will briefly discuss the pros and cons of rateless codes in area of P2P file-sharing and live video streaming. The proposed discussion will be based on our recent results obtained from practical experimental and prototyping activities carried over the Planetlab platform. Contact: Luigi Liquori (Luigi.Liquori@inria.fr)
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