An Incentive Mechanism for Message Relaying in Peer-to- Peer Discovery

Peer discovery via distributed message relaying is an important function of a P2P system in which the resources/services provided by peers and service/resource providers may change frequently. The usual searching protocols create huge burden on communications or cause long response time. Appropriate incentives are required to avoid free-riding and achieve efficient cooperations in message relaying. We present an incentive mechanism that aims at solving both the efficiency and incentive problems of message relaying for peer discovery. In this mechanism rewards are passed from upstream nodes to downstream nodes. A peer is rewarded if a service provider is found via a relaying path composed of this peer. The mechanism allows peers to specifically trade off communication efficiency and reliability, and maintains anonymity and information locality. Some analytical insights are given to the subgame perfect Nash equilibria (SPNE) and best response strategies of this game. An approximation approach is provided to calculate a symmetric SPNE. Experiments show that this incentive mechanism brings a system utility higher than in breadth-first search, and close to the optimal utility in a centralized system. In the incentive mechanism the distribution of relaying efforts over hops is dependent on the convexity of the cost function. With the cost function more convex, peers in earlier hops tend to spend more efforts on relaying.