Research On Resource Management Mechanism In Peer-to-Peer System

The past several years witness the rapid development of P2P systems. Efficient resource management scheme becomes the key technology of P2P systems. On one hand, the fact that the construction of P2P overlay network doesn't consider the real network situation of physical layer leads to the mismatch of overlay layer and physical layer, which makes the latency and the cost of locating resources increase. At the same time, the characteristics of dynamics and anonymity of P2P can't ensure that all the peers will provide honest services and reliable resources. On the other hand, although structured P2P systems have good scalability, the main issue exists in them is that they are stricted to exact match and don't support content based query. All these problems prohibit the rapid development of P2P systems. How to reduce searching cost and decrease the latency of locating resources and how to construct a safe efficient P2P system that supports content based query becomes an important subject of the P2P system research field.Resource management scheme in P2P system has four componets: physical transport layer, P2P overlay network layer, file management layer and information retrieval model. The main topics in this dissertation are the last three parts. P2P overlay network layer focuses on the construction and optimization of P2P protocols. Currently, there exist many problems in P2P system, which are high searching cost, long locating latency and hidden troubles that are brought by anonymity. Then, how to construct a fast, efficient and safe overlay network is challenging. File management layer aims at managing data depository, dividing the files efficiently according to keywords set and providing efficient mapping from file to P2P overlay network layer. The main issue to implement mapping from semantic layer to P2P layer is the mismatch of dimensions. How to reduce dimensions still needs further investigation. Information retrieval model mainly deals with the insertion and deletion of files and calculates the similarity between documents. The curse of dimensionality and the high dimension sparse matrix are the main issues to resolve when dealing with the documents. Detailed research works have been done on the above issues. The main contributions are as follows.As current construction of most P2P systems doesn't take the physical elements into considerations, a bidirectional Chord system based on latency-sensitivity is proposed to decrease the latency and cost of resources locating. This system partitions the nodes according to the latencies among these nodes and the landmarks to decrease the average response time. And by the means of bidirectional query algorithm on Chord, the search path length is reduced.To the problem of hostile service brought by node anonymity in P2P system, this disertation proposed a reputation aware resource finding algorithm. This algorithm is based on Directed-BFS algorithm and adopts the conception of reputation to efficiently restrain the deceiving behavior of hostile nodes in P2P system and reduce the messages load in the system, which can ensure the reliability and safety of the services.To reduce the affection of Sybil attack on P2P system, a Sybil defense mechanism based on small world is proposed. Inducing the difficulty of finding Sybil group to max-flow/min-cut problem, this dissertation uses crawler to find Sybil group by adopting an artificial vertex, which can effectively isolate the Sybil attacker nodes from P2P system.To solve the problem of existing DHÎ¥-based file storage systems being restricted to exact match and lacking semantic-based query, a DHT-based file storage system named FCAN is proposed in this paper. Mapping a document vector from semantic space to P2P space by FastMap, FCAN can effectively reduce the dimensions of document vector to implement semantic-based query without affecting the semantic integrality of this document. By clustering the nearest neighbors based on centriod, FCAN is further improved to reduce the redundant messages and searching time.As the main issues that affect query efficiency and searching cost in content-based P2P search system are the complexity of computing the similarity of the documents brought by high dimensions and the great deal of redundant messages coming with flooding. This dissertation defines the document similarity by the way of set distance. This method restrains the complexity of computing the document similarity in linear time. Also, this dissertation clusters the peers based on content by their set distance to reduce the query time and redundant messages.Simulation results show that the resource management schemes presented in this dissertation not only reduce the searching cost and decrease the latency to locate resources in P2P system effectively, but also provide content-based query and ensure the safety of the whole system.