Game Theoretic Analysis of P2P Systems Daniel Chen December 4, 2003 GE 493RS

Problem What is P2P? Peer-to-peer (P2P) networks are self- organizing non-cooperative distributed systems Problem How to create a P2P system that promotes participation among users while being robust to cheating (“freeloading”)?

Game Theoretical Model Cournot Duopoly/Oligopoly All peers derive equal benefit from everybody else Therefore, we can reduce the problem to a 2-player game from the symmetry of all players Repeated static game Stage corresponding to discretized time slots At each stage both players will maximize its payoff Strategy space is available resource to contribute

Game Theoretical Model Design payoff function of the P2P system U=Incentives – Costs Incentives: Worth of contributing storage resource Costs: Bandwidth consumption of contributing storage

Incentive/Cost Engineering Engineering incentives and costs of P2P systems Mechanism Design Control-theoretic approach Decentralized optimal controller Payoff function to be used also as the optimization objective function of the control system Locally adapt decisions on their contribution quantity

Results

Criticism Suitable (enforceable) metrics for contributions Communication/computational overhead in playing the game Account for network condition dynamics in playing with peers

Conclusion Game theoretic modeling of P2P systems using the Cournot (Duopoly/Oligopoly) model Payoff Design One set of results showing more benefit for more contributions Closing Thoughts…