Impact of Feedback on Trust in P2P Networks

Feedback plays an important role in P2P trust systems. Existing trust systems usually assume that most of normal peers have idealized feedback behaviors, that is, peers can provide honest feedback after download immediately. However, studies show that feedback sparsity and delay widely exist in a real P2P network. Unfortunately, their effect on trust systems has received little attention in previous researches. In this paper, we propose a feedback model considering feedback ratio and feedback delay to analyze the effect. We find that most trust systems have poor reliability when the number of feedbacks is small in a decentralized P2P network. We propose an implicit feedback mechanism based on the retention time of files to remove the impact of user feedback on trust systems. Simulation results show that trust systems using implicit feedback can not only effectively isolate normal peers from malicious peers but also provide differential services for normal peers with different behaviors.