Research On Search Algorithm And Trust Mechanism In Unstructured P2P

Unstructured Peer-to-Peer (hence P2P) applications are very popular on the Internetover the last few years, such as Gnutella, KaZaa. In general, they employ ?ooding schemefor searching object, so that a lot of bandwidth is wasted and their scalability is poor. Atsame time, the open accessibility of these systems make them vulnerable to malicious userswishing to poison the system with corrupted data or harmful services and worms. To mit-igate the adverse behavior of unreliable or malicious peers in a network, researchers havesuggested using trust mechanisms. So, Search algorithm and trust mechanism are two keycomponents that are widely studied in unstructured P2P.The main contributions of this dissertation are as follows:1. We study the spread mechanisms and the key role of high degree nodes in the unstruc-tured P2P, and propose that the system performance can be improved by utilizing highdegree nodes. We present an overview of several spread mechanisms for unstructuredP2P and analyze the performance of them.2. Based on random walk and high degree walk spread mechanism, we propose foursearch methods, and analyze the performance of them. Extensive simulation resultsshow that they performs very well on the Gnutella-like networks, and are robust to thefailure of high degree nodes.3. To mitigate the adverse behavior of unreliable or malicious peers, we study the repu-tation model, and propose a reputation model based on social rules. At same time, wepresent the computing method of the parameters of our reputation model. The attackssimulation show that this reputation model effectively mitigates endanger of maliciouspeers.4. Based on our reputation model, we design a trust mechanism in unstructured P2P. Wedesign the storage and search mechanism of evaluation record of peers, and presentan algorithm of topology evolution based on trust. Extensive simulation results show that this trust mechanism can effectively improve the performance of unstructured P2Psystems.5. We propose NotificationBroker cluster in WS-Notification service build on unstruc-tured P2P technique, and it has good dynamic characteristic, good scalability and isrobust to random node failure. We present that NotificationBroker cluster is managedas a logical multi-layer system based on Topic. We also design a gossip-based broad-cast algorithm for spreading notification message in the topic layer, and simulationresults show that it has high reliability.