How do we encourage an egoist to act socially in an ad hoc mobile network?
We consider a flow-based model for an ad hoc mobile network where users may need to use transit nodes in order to be able to communicate. Under the assumption that every node is willing to cooperate, we derive the set of Karush-Kuhn-Tucker equations that define the socially-optimal flows on each of the routes. We then look at the problem from an 'egoist' point of view, in which the user at node i cares only about maximising his/her utility under the constraint that the flows on routes which do not use node i are fixed at the socially-optimal value.This leads us to a consideration of extra constraints that could be introduced to induce the egoist user at node i to behave in a socially-optimal way. We show how to derive the parameters of such constraints, and give them interpretations in terms of schemes in which nodes' transmission rates are constrained by the rates at which they accumulate 'credit'.