Time Dependent Message Spraying for Routing in Intermittently Connected Networks

Intermittently connected mobile networks, also called Delay Tolerant Networks (DTNs), are wireless networks in which at any given time instance, the probability of having a complete path from a source to destination is low. Several routing algorithms have been proposed for such networks based on control flooding in which there is a fixed number of copies for each message. Although a DTN is delay tolerant by definition, often there is an upper bound imposed on message delivery delay. In this paper, we propose a novel spraying algorithm in which the number of message copies in the network depends on the urgency of meeting the expected delivery delay for that message. The main objective of this algorithm is to give a chance to early delivery with small number of copies in existence, consequently decreasing the average number of copies sprayed in the network. We derive the formula for the optimum borders of periods for spraying for two-period and three-period variants of our algorithm. We also present simulations of the method and compare their results with the analytical ones and observe the good match between them. Furthermore, we demonstrate that time dependent spraying algorithm provides a significant decrease in average copy count per message while preserving the percentage of the messages delivered before the upper bound of the acceptable delay expires.