On using reputations in ad hoc networks to counter malicious nodes

Nodes in mobile ad hoc networks have a limited transmission range. Hence the nodes expect their neighbors to relay packets meant for far off destinations. These networks are based on the fundamental assumption that if a node promises to relay a packet, it will relay it and will not cheat. This assumption becomes invalid when the nodes in the network have tangential or contradictory goals. The reputations of the nodes, based on their past history of relaying packets, can be used by their neighbors to ensure that the packet will be relayed by the node. This paper introduces a reputation scheme for ad hoc networks. Instead of choosing the shortest path to the destination, the source node chooses a path whose next hop node has the highest reputation. This policy, when used recursively, in the presence of 40% malicious nodes, improves the throughput of the system to 65%, from 22% throughput provided by AODV. This improvement is obtained at the cost of a higher number of route discoveries with a minimal increase in the average hop length.