Peer-to-Peer Grids

We describe Peer-to-Peer Grids built around Integration of technologies from the peer-to-peer and Grid fields. We focus on the role of Web services linked by a powerful event service using uniform XML interfaces and application level routing. We describe how a rich synchronous and asynchronous collaboration environment can support virtual communities built on top of such infrastructure. Universal access mechanisms are discussed. 1 Peer-to-Peer Grids There are no crisp definitions of Grids [1,2] and Peer-to-Peer Networks [3] that allow us to unambiguously discuss their differences and similarities and what it means to integrate them. However these two concepts conjure up stereotype images that can be compared. Taking “extreme” cases, Grids are exemplified by the infrastructure used to allow seamless access to supercomputers and their datasets. P2P technology is exemplified by Napster and Gnutella, which can enable ad hoc communities of low-end clients to advertise and access the files on the communal computers. Each of these examples offers services but they differ in their functionality and style of implementation. The P2P example could involve services to set-up and join peer groups, browse and access files on a peer, or possibly to advertise one’s interest in a particular file. The “classic” grid could support job submittal and status services and access to sophisticated data management systems. Grids typically have structured robust security services while P2P networks can exhibit more intuitive trust mechanisms reminiscent of the “real world”. Again Grids typically offer robust services that scale well in pre-existing hierarchically arranged organizations; P2P networks are often used when a best effort service is needed in a dynamic poorly structured community. If one needs a particular “hot digital recording”, it is not necessary to locate all sources of this; a P2P network needs to search enough plausible resources that success is statistically guaranteed. On the other hand, a 3D simulation of the universe might need to be carefully scheduled and submitted in a guaranteed fashion to one of the handful of available supercomputers that can support it. In this article, we explore the concept of a Peer-to-Peer Grid with a set of services that include those of Grids and P2P networks and support naturally environments that have features of both limiting cases. We can discuss two examples where such a model is naturally applied. In High Energy Physics data analysis (e-Science [4]) problem discussed in chapter of Bunn and Newman, the initial steps are dominated by the systematic analysis of the accelerator data to produce summary events roughly at the level of sets of particles. This Grid-like step is followed by “physics analysis” which can involve many different studies and much debate between involved physicists as to appropriate methods to study the data. Here we see some Grid and some P2P features. As a second example, consider the way one uses the Internet to access information – either news items or multimedia entertainment. Perhaps the large sites like Yahoo, CNN and future digital movie distribution centers have Grid like organization. There are well-defined central repositories and high performance delivery mechanisms involving caching to support access. Security is likely to be strict for premium channels. This structured information is augmented by the P2P mechanisms popularized by Napster with communities sharing MP3 and other treasures in a less organized and controlled fashion. These simple examples suggest that whether for science or commodity communities, information systems should support both Grid and Peer-to-Peer capabilities [5,6]. In Sec. 2, we describe the overall architecture of a P2P Grid emphasizing role of Web services and in Sec. 3, describe the event service appropriate for linking Web Services and other resources together. In the following two sections, we describe how collaboration and universal access can be incorporated in this architecture. The latter includes the role of portals in integrating the user interfaces of multiple services. The chapter by Pallickara and Fox includes a detailed description of a particular event infrastructure. 2 Key Technology Concepts for P2P Grids