Structured and unstructured overlays under the microscope

Motivation and Approach

Peer-to-peer Internet applications for data sharing have gained in popularity over the last few years to become one of today's main sources of Internet traffic. Their peer-to-peer approach has been proposed as the underlying model for a wide variety of applications, from storage systems and cooperative content distribution to Web caching and communication infrastructures. Existing peer-to-peer systems rely on overlay network protocols for object storage/retrieval and message routing. These overlay protocols can be classified broadly as either structured or unstructured based on the constraints imposed on how peers are organized and where stored objects are kept. The research community continues to debate the pros and cons of these alternative approaches [pdf].

We contribute to this discussion the first multi-site, measurement based study of two operational and widely deployed P2P file-sharing systems. The two protocols - the unstructured Gnutella and the structured Overnet - were evaluated in terms of resilience, message overhead, and query performance. We validate our findings and further extend our conclusions through detailed analysis and simulation experiments.