Chapter 3. Unstructured Overlays

Most deployed P2P applications have used unstructured topologies. Here we look at this important class of overlay in detail, starting with the basic routing mechanisms. Then we discuss the theory of various types of unstructured graphs such as random graphs, power-law random graphs, and scale-free graphs. Influential designs such as Gnutella, Freenet, Fastrack, and Gia are then discussed. Ideas from social networks, especially the small-world phenomenon, are related to unstructured topologies, and an overview of social overlays follows. The chapter concludes with a brief look at how an experimental overlay emulator implements its routing layer.

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