Delay management in delay-tolerant networks

In delay-tolerant networks (DTN), nodes explore various opportunities to connect and communicate with each other. A series of encounters of different nodes will create such opportunities and spread a message among many nodes and eventually deliver to the designated destination. We study one common DTN scenario where the message exchanges happen when nodes meet others at certain locations. In this situation, the success of message delivery and the quality of the delivery depend highly on the likeliness of nodes' encounters and time elapsed between encounters. We study two important qualities of service requirements: the probability of two nodes meeting each other (encounter probability) and the time it takes for two nodes to meet (encounter delay). The key considerations are how nodes pick their next locations (mobility patterns) and the features of the dwell time. In this paper, we will study several mobility patterns, including random movement, and activity agenda based movement. We also study an additional message delivery constraint, i.e., a message will be dropped if not delivered within a limited number of locations visited. We develop mathematical formulas using Markov chain as a main tool. Our work is presented as an illustration through case studies. The methodology applies to mobility models alike and is extendable to real trace analysis. We present numerical results when closed form formulas cannot be acquired. Our results help the management of message delivery for DTN, e.g., in selecting a proper time-to-live threshold for a message. Copyright (C) 2008 John Wiley & Sons, Ltd.