The Design of A Distributed Rating Scheme for Peer-to-peer Systems

There exist many successful examples of online reputation (or rating) systems, such as on-line markets and e-tailer ratings. However, for peer-to-peer applications, an explicit ratings subsystem has often been ignored in system design because of the implicit assumption of trust and altruism among P2P users. This assumption might be true (or might not matter) when a P2P network is still in its infancy and is relatively small in size. But the assumption might break down with increase in the size and diversity of the P2P network. In this paper, we discuss issues in the design of rating schemes for P2P systems. In keeping with the design philosophy of many of these system, we consider the design of distributed rating systems. As a case study, we illustrate two different approaches to a distributed rating system aimed at tackling the free-rider problem in P2P networks. A key challenge in designing such rating schemes is to make them collusion-proof: we discuss our efforts in this direction.