Structured and Unstructured Overlays under the Microscope: A Measurement-based View of Two P2P Systems That People Use

Existing peer-to-peer systems rely on overlay network protocols for object storage and retrieval and message routing. These overlay protocols can be broadly classified as structured and unstructured – structured overlays impose constraints on the network topology for efficient object discovery, while unstructured overlays organize nodes in a random graph topology that is arguably more resilient to peer population transiency. There is an ongoing discussion on the pros and cons of both approaches. This paper contributes to the discussion a multiple-site, measurement-based study of two operational and widelydeployed file-sharing systems. The two protocols are 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.