Building Robust Peer-to-Peer Information Dissemination Systems Using Trust and Incentives

Abstract

As computers become pervasive and better connected, the popularity of peer-to-peer computing has grown immensely. The sharing of unused resources at peers is desirable and practically important because they can collectively comprise a powerful system. The potential benefit, however, can be undermined by uncooperative behavior of some peers because they are managed individually and hence may not follow the expected protocols. To build robust systems, we must incorporate proper trust and incentive mechanisms so that peers would rather cooperate. In this dissertation, we demonstrate that building robust peer-to-peer information dissemination systems is important and viable, using four concrete cases. First, we investigate the incentive mechanism of BitTorrent, an exchange-based file distribution protocol. Our framework based on iterated prisoner's dilemma provides an insight into users' tension between eagerness to download and unwillingness to upload. By using both analytical and experimental approaches, we show that the current incentive mechanism of BitTorrent is susceptible to free riding. We propose an improved mechanism that punishes free riders effectively. Second, we present a trust-aware overlay multicast system that performs well in the presence of uncooperative nodes, which may block, delay, fabricate, or forge the messages they forward. We develop (1) a set of protocols that detect uncooperative behavior, (2) a scheme of trust value assignment according to the behavior of nodes, and (3) an algorithm that adapts the multicast tree based on trust values, all of which allows the system to remain stable and responsive over time. Third, we propose an alternative news feed dissemination system, called FeedEx, in which feed subscribers mesh into a network and exchange news feeds with neighbors. The collaborative exchange in FeedEx, with the help of the incentive-compatible design using the pair-wise fairness principle, reduces the server load and hence increases the scalability. Fourth, we introduce a new concept of peer-to-peer computing, that is, continual service using ephemeral servers. To this end, we develop a system model for the concept and implement a discrete-time simulator to find the conditions and the system support for eliciting cooperation. All four cases are substantiated by experimental results.