Toward a Synergy Between P2P and Grids Domenico Talia and Paolo Trunfio University of Calabria, Italy Peer-to-peer (P2P) networks and grids are distributed computing models that enable decentralized collaboration by integrating computers into networks in which each can consume and offer services. P2P is a class of self-organizing systems or applications that takes advantage of distributed resources – storage, processing, information, and human presence – available at the Internet's edges. A grid is a geographically distributed computation platform comprising a set of heterogeneous machines that users can access through a single interface. Both are hot research topics because they offer promising paradigms for developing efficient distributed systems and applications. Unlike the classic client-server model, in which roles are well separated, P2P and grid networks can assign each node a client or server role according to the operations they are to perform on the network – even if some nodes act more as server than as client in current implementations. In analyzing both models, we discover that grids are, in essence, P2P systems. Although many aspects of today's grids are based on hierarchical services, this is an implementation detail that should be removed in the near future. As grids used for complex applications increase from tens to thousands of nodes, we should decentralize their functionalities to avoid bottlenecks. The P2P model could thus help to ensure grid scalability: designers could use the P2P philosophy and techniques to implement nonhierarchical decentralized grid systems. In spite of current practices and thoughts, the grid and P2P models share several features and have more in common than we perhaps generally recognize. As Ian Foster and Adriana Iamnitchi point out (dsl.cs.uchicago.edu), a broader recognition of key commonalities could accelerate progress in both communities. It is time to consider how to integrate these two models. A synergy between the two research communities, and the two computing models, could start with identifying the similarities and differences between them. Basics In the past few years, P2P has attracted enormous media attention and gained popularity by supporting two main classes of applications: • file sharing, in which peers share files with each other (Napster and Gnutella for music, for example) • highly parallel computing, in which an (inherently) parallel application runs on available nodes (SETI@home and FightAIDS@home, for example). Apart from these well-known systems, the P2P model is emerging as a new distributed paradigm because of its potential to harness the computing, storage, and communication power of hosts in the network to make their underutilized resources available to others. P2P