Self-Organizing Topology Adaptation in Peer-to-Peer Networks

The peers in a Peer-to-Peer (P2P) system arrange themselves in a virtual network called the overlay network. The overlay network sits above the underlying physical network and is used to search for resources and peers, and to route messages between peers. The topology of the overlay network is the graph whose vertices are the peers and whose edges are the connections between the peers. The choice of topology affects application performance and the correct choice depends on the application. The literature contains examples of topologies that can be used to implement various types of applications. Topology adaptation algorithms are used to maintain an overlay network’s topology as per application requirements. Early P2P applications either did not use topology adaptation algorithms or used simple solutions based on a centralized component that results in poor fault-tolerance and scalability. Since 2002, decentralized algorithms have been proposed that may be used to create and maintain specific topologies. Although this is certainly an improvement, these algorithms are typically designed to create a specific topology for a specific application and are therefore not generally applicable or easily reusable. As a result, topology adaptation algorithms have to be designed from scratch and an application that has been developed using an existing algorithm cannot be altered easily to create and maintain a new topology. This thesis presents a general approach to decentralized topology adaptation in unstructured P2P overlay networks. The approach is based on a single abstract algorithm called the PEer-to-peer Self-organizing TOpology (PESTO), which can be used