On Incentive Machanism Techniques Study Towards The Node Selfishness In P2P Networks

P2P systems become increasingly popular since its scalability with no central infrastructure, however, the inherited characteristics, such as open, free and self-organization etc, cause the selfish behavior of participant nodes. The selfishness and free-riding phenomenon have become a crucial problem and one of the important factors of limiting P2P network development. The incentive mechanism aimed to suppress the node selfishness and encourage the cooperation between nodes, is proposed by researchers to promote the node to contribute, and guarantee the effectiveness of P2P network offering high-efficient, reliable service ability. However, traditional incentive studying often needs a central server or the complicated system infrastructure in the past, leading to large expenses and cost.Based on current status and tendency of incentive mechanism research, we address several critical problems in distributed Peer-to-Peer environment, especially in three important stages:the topology construction and maintenance stage; content distribution stage and routing and message transmission stage. The contribution of this dissertation includes:1. Propose a reciprocated contribution capacity based topology optimization approach. The topology structure of p2p network is a basic assurance of high-efficient performance for resource search. In literature, little attention has been paid on the selfishness effects of topology. In order to tackle the problems that selfish (malicious) nodes occupy the center of the P2P network resulting in inefficient network performance, a local historical transaction based Reciprocal Contribution Capacity (RCC) of peers and an effective topology optimization approach (RCTO) is proposed. It is desirable for RCTO to establish connections between peers with higher RCC. Otherwise, selfish nodes would be recognized and forced to the marginal of P2P network. It is shown through experiments that RCTO can greatly shorten the search hops for authentic resource. Compared with counterpart RC-ATP, RCTO achieves higher resource distribution efficiency and incurs less cost.2. Propose a contribution willingness-based two phase bandwidth resource allocation approach (Cowtra). Previous studies addressing the free-rider problems focus on how to utilize peer absolute contribution to differentiate services quality, while neglecting the role of relative contribution of peers, leading to unfairness of resource (e.g bandwidth) allocation. At first stage of Cowtra, our approach guarantees the bandwidth of a source peer is distributed properly according to the peer contribution using social warfare maximum mechanism. Then at second stage, an iterative bandwidth micro adjustment process is conducted to softly reassign the amount of received bandwidth, with regard to the peer's relative contribution, namely Willingness of Contribution (WoC). In this way, a rational peer would try to act more contributive and cooperative to get a better result. Cowtra promotes the fairness of bandwidth allocation, as peers get the resource in proportion with their contribution and WoC. Simulations demonstrate that Cowtra largely increases the fairness of bandwidth allocation and improve the peer utility in overall system.3. Propose a belief-based message relaying cooperative strategy. Known the cooperation between the nodes to relay messages unselfishly is the foundation that the whole p2p system operates steadily, we study the message-relay problem by modeling it as a repeated game with imperfect observation and under erroneous-prone judgment environment, and propose a strategy only relying on node's own historical actions and its private imperfect observation of other node's information. Then node updates the belief of the others cooperative action using Bayes's rule, and take a proper action to maximization its long-term payoffs. Simulation and analysis demonstrate that selfish node who deviates from the proposed strategy can't obtain any extra income, and this method guarantees that the cooperative node gets the average income higher than the selfish node.