Search and replication in unstructured peer-to-peer networks

Decentralized and unstructured peer-to-peer networks such as Gnutella are attractive for certain applications because they require no centralized directories and no precise control over network topology or data placement. However, the flooding-based query algorithm used in Gnutella does not scale; each individual query generates a large amount of traffic and large systems quickly become overwhelmed by the query-induced load. This paper explores various alternatives to Gnutella's query algorithm and data replication strategy. 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 magnitude in many cases. We also present a distributed replication strategy that yields close-to-optimal performance.