Abstract Decentralized and unstructured peer-to-peer networks such as Gnutella are attractive for certain applicationsbecause they require no centralized directories and no precise control over network topologies and data placement. However, the flooding-based query algorithm used in Gnutella does not scale; each individual query gener-ates a large amount of traffic and, as it grows, the system quickly becomes overwhelmed with the query-induced load. This paper explores, through simulation, various alternatives to gnutella's query algorithm, data replicationmethod, and network topology. We propose a query algorithm based on multiple random walks that resolves queries almost as quickly as gnutella's flooding method while reducing the network traffic by two orders of mag-nitude in many cases. We also present a distributed replication strategy that yields close-to-optimal performance. Finally, we find that among the various network topologies we consider, uniform random graphs yield the bestperformance. 1 Introduction The computer science community has become accustomed to the Internet's continuing rapid growth, but even tosuch jaded observers the explosive increase in Peer-to-Peer (P2P) network usage has been astounding. Within a few months of Napster's [12] introduction in 1999 the system had spread widely, and recent measurement data suggeststhat P2P applications are having a very significant and rapidly growing impact on Internet traffic [11, 15]. Therefore, it is important to study the performance and scalability of these P2P networks. Currently, there are several different architectures for P2P networks:

this paper, we introduce a new software framework that enhances the performance of Message Passing Interface (MPI) applications through an adaptive middleware for load balancing that includes process checkpointing and migration. Fields as diverse as fluid dynamics, materials science, biomechanics, and ecology make use of parallel adaptive computation. Target architectures have traditionally been supercomputers and tightly coupled clusters. This framework is a first step in allowing these computations to use computational grids e#ciently

Large-scale, dynamic, and heterogeneous networks of computational resources promise to provide high performance and scalability to computationally intensive applications, but these environments also introduce the need for complex resource management strategies. This paper introduces actor-based programming abstractions and a middleware framework to relieve developers from considering non-functional concerns while allowing middleware layers to optimize application performance and global resource utilization. The Internet Operating System (IOS) consists of a peer-to-peer virtual network of middleware agents that trigger application component reconfiguration based on changes in the underlying physical network and based on the application communication patterns and resource consumption. IOS middleware agents are highly customizable to account for different resource profiling, load balancing, and peer-to-peer interconnection policies.

Abstract In many Internet applications, requests for a certain object are routed bottom-up over a tree where the root of the tree is the node containing the object. When an object becomes popular, the root node of the tree may become a hot-spot. Therefore many applications allow intermediate nodes to acquire the ability to serve the requests, for example by caching the object. We call such distinguished nodes primed. We propose and analyze different algorithms where nodes decide when to become primed; these algorithms balance the maximum load on a node and the number of primed nodes. Many applications require both fully distributed decisions and smooth convergence to a stable set of primed nodes. We first present optimal algorithms which require communication across the tree. We then consider the natural previously proposed threshold algorithm, where a node becomes primed when the incoming flow of requests exceeds a threshold. We show examples where threshold exhibits undesirable behavior during convergence. Finally, we propose another fully distributed algorithm, gap, which converges gracefully. 1 Introduction The Internet provides a platform for decentralized applications where content or services are requested, stored, and provided by very large number of loosely coupled hosts. In these applications, there is no centralized support. Requests are forwarded from peer to peer, and each peer can become a server for each item.

Modern distributed computing requires a secure framework capable of free code mobility. In this paper, we present a simple lambda-based actor language with extensions for mobility and security, as well as the operational semantics to reason about these topics in distributed systems. Finally, we describe our preliminary implementation results. 1.

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