How the Contact-Probing Mechanism Affects the Transmission Capacity of Delay-Tolerant Networks

Link duration is a main factor in determining the transmission capacity between two encounter nodes in delay-tolerant networks (DTNs). Existing research on DTN transmission capacity usually assumes that a node can immediately discover the nodes that move into its transmission range. Under this assumption, the link duration in DTNs is determined by the moving speed and transmission distance of encounter nodes. However, this assumption may be invalid in realistic DTNs, where the nodes use a contact-probing protocol to detect their neighbors. In this paper, we investigate the impact of contact-probing mechanisms on link duration and, thus, the transmission capacity of DTNs. We first derive the probability distribution of link duration and analyze the impact of contact-probing mechanisms on the total link durations. Based on this approach, we derive the theoretical node throughput and energy consumption and explore their tradeoff. In addition, we provide a framework for computing the optimal contact-probing frequency under energy limitations and adjust the probing frequency according to the node-encountering rate. Simulation experiments based on the Opportunistic Network Environment simulator validates the correctness and the accuracy of our analytical model. Our analytical results provide insights into how contact probing affects the DTN transmission capacity and energy consumption.