The Effect of Mobility on Cooperation in Ad Hoc Networks

1. The Effect of Mobility on Cooperation in Ad Hoc Networks Márk Félegyházi1, Jean-Pierre Hubaux1,Levente Buttyán2 1École Polytechnique Fédérale de Lausanne – Laboratory for Computer Communications and Applications 2Budapest University of Technology and Economics – Laboratory of Cryptography and System Security Ad hoc networks Game-theoretic model for packet forwarding self-organizing network each networking service is provided by the nodes • mobile network scenario • we assume that the nodes are rational • time is divided into time slots We focus on packet forwarding Problem of non-cooperation Concept: The node plays against the rest of the network Nodes are selfish = they try to save resources by not contributing to packet forwarding. Incentive techniques to stimulate cooperation No authentication of the nodes is needed Question:Do we need these incentive mechanisms or can cooperation exist based on the self-interest of the nodes? Interaction: Result βi (k): benefit of node i until step k γi (k): contribution of node i until step k ρi (k): interaction ratio of node i until step k Strategy: For each step k: IF ρi (k) ≥ кiFORWARD in step k+1 ELSE DROP in step k+1 The Generous Tit-For-Tat (GTFT) strategy: L: average length of the connections g: generosity of the node Step duration increases => mobility increases 1. Required generosity decreases as mobility increases. Hence, mobility has a beneficial effect on cooperation. 2. But, generosity is always needed to bootstrap cooperation. Goal of the nodes: Conclusion B: benefit for node i if a packet arrives C: cost for node i if it forwards a packet Incentive techniques are required to motivate nodes to cooperate in a mobile ad hoc network.