Search, Replication and Grouping for Unstructured P2P Networks
Speaker: Dimitrios Tsoumakos
Date: 18 March 2008 Time: 14:00-16:00
Location: "Mediterranean Studies" Seminar Room, FORTH, Heraklion, Crete
Host: Euaggelos Markatos


Peer-to-Peer (P2P) networks are gaining increasing attention from both the scientific and the large Internet user community. Popular applications utilizing this new technology offer many attractive features to a growing number of users. P2P systems have two basic functions: Content search and dissemination. Search (or lookup) protocols define how participants locate remotely maintained resources. In data dissemination, users transmit or receive content from single or multiple sites in the network.

P2P applications traditionally operate under purely decentralized and highly dynamic environments. Unstructured systems represent a particularly interesting class of P2P networks. Peers form an overlay in an ad-hoc manner, without any guarantees relative to lookup performance or content availability. Resources are locally maintained, while participants have limited knowledge, usually confined to their immediate neighborhood in the overlay.

My work aims at providing effective and bandwidth-efficient searching and data sharing. We present a suite of algorithms which provide peers in unstructured P2P overlays with the state necessary in order to efficiently locate, disseminate and replicate objects identified by a unique ID. The Adaptive Probabilistic Search (APS) scheme utilizes directed walkers to forward queries on a hop-by-hop basis. Peers store success probabilities for each of their neighbors in order to efficiently route towards object holders. AGNO performs implicit grouping of peers according to the demand incentive and utilizes state maintained by APS in order to route messages from content holders towards interested peers, without requiring any subscription process. Finally, the Adaptive Probabilistic REplication (APRE) scheme expands on the state that AGNO builds in order to replicate content inside query intensive areas according to demand.


Graduated from NTUA ECE Dept in '99, joined the CS Dept of University of Maryland in Fall 2000, (1 year at NTUA with T. Sellis). MS and PhD in Comp Sci under Dr. Roussopoulos (00-06). From October 06 till now im a senior researcher at the computing systems Lab of NTUA (cslab@ntua), in charge of the GREDIA project (FP6).

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