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We can identify two types of uncooperative nodes: faulty/malicious nodes and selfish nodes. By saying faulty/malicious nodes, we refer to the broad class of nodes that are either faulty and therefore cannot follow a protocol, or are intentionally malicious and try to attack the system. The problems of faulty/malicious nodes need to be addressed from many layers, for example, using spread-spectrum encoding to avoid interference over the communication channel; using a reputation system to identify the faulty/malicious nodes and subsequently avoid or penalize such nodes [4]; and applying the techniques from faulttolerant computing to perform computation correctly even in the presence of faulty/malicious nodes. Although the problems of faulty/malicious nodes can be important. | Sprite A Simple Cheat-Proof Credit-Based System for Mobile Ad-Hoc Networks Sheng Zhong Computer Science Department Yale University New Haven CT 06520 Email sheng.zhong@yale.edu Jiang Chen Computer Science Department Yale University New Haven CT 06520 Email jiang.chen@yale.edu Yang Richard Yang Computer Science Department Yale University New Haven CT 06520 Email yry@cs.yale.edu Abstract Mobile ad hoc networking has been an active research area for several years. How to stimulate cooperation among selfish mobile nodes however is not well addressed yet. In this paper we propose Sprite a simple cheat-proof creditbased system for stimulating cooperation among selfish nodes in mobile ad hoc networks. Our system provides incentive for mobile nodes to cooperate and report actions honestly. Compared with previous approaches our system does not require any tamperproof hardware at any node. Furthermore we present a formal model of our system and prove its properties. Evaluations of a prototype implementation show that the overhead of our system is small. Simulations and analysis show that mobile nodes can cooperate and forward each other s messages unless the resource of each node is extremely low. I. Introduction IN recent years mobile ad hoc networks have received much attention due to their potential applications and the proliferation of mobile devices 1 2 . Specifically mobile ad hoc networks refer to wireless multi-hop networks formed by a set of mobile nodes without relying on a preexisting infrastructure. In order to make an ad hoc network functional the nodes are assumed to follow a self-organizing protocol and the intermediate nodes are expected to relay messages between two distant nodes. Recent evaluations have shown that ad hoc networks not only are flexible and robust but also can have good performance in terms of throughput delay and power efficiency 3 . So far applications of mobile ad hoc networks have been envisioned mainly for emergency and military .
