Optimizing Time-Variant Quota-Controlled Routing in Delay-Tolerant Networks

Delay-tolerant networks (DTNs) are wireless mobile networks that exhibit frequent intermittent connectivity and large transmission delay among nodes. Research results have shown that quota-controlled routing protocols can strike a reasonable balance between routing performance and cost, where quota is a value to control the number of message copies. However, the question of how to set the optimal quota dynamically in order to achieve the lower bound of routing cost is still open. In this paper, we model the optimization of quota control as an extremal functional problem and analyze it by a classic mathematical method called Calculus of Variations (CoV) for the first time. The function of time-variant quota with minimal average number of message copies is obtained in closed form, and an optimal quota control algorithm is proposed under practical routing design considerations. Both the numerical and simulation results show that the proposed model and algorithm are effective and efficient.