The Cost of Altruistic Punishment in Indirect Reciprocity-based Cooperation in Mobile Ad Hoc Networks

Reciprocity-based cooperation on packet forwarding in mobile ad hoc networks means that before passing on a packet to the next hop intermediate nodes verify whether the sender of the packet is trustworthy (i.e., cooperative in the past) or not. One of the key questions is what data should be used to evaluate the trustworthiness. This paper demonstrates that if cooperation is based on indirect reciprocity and a classic watchdog-based mechanism for data collection is used, discarding packets can be seen as an act of altruistic punishment. An intermediate node that decides to discard packets from a selfish sender pays the cost (expressed in decrease of trustworthiness among other nodes). However, if the cost of punishing free-riders is too high then nobody has the incentive to be the punisher. This paper demonstrates that the cost is significant and reduces an overall performance of the network. Using computational experiments it is shown that a simple modification of the classic watchdog-based trust data collection mechanism can result in minimisation of the cost and improvement of the throughput of the network.