Data Delivery in Delay Tolerant Networks: A Survey

Delay-Tolerant Networks (Fall (2003)), also called disruption tolerant networks (DTNs), represent a fairly new networking paradigm that allows inter-connection between devices that current networking technology cannot provide. There are a wide variety of networks where an end-to-end connection between a given source and destination may never be present. Consequently, traditional routing protocols cannot be directly applied in these scenarios for delivering data. However, if one were to take the graph formed by the nodes based on their connectivity dictated by their radio range and consider the overlap not only over space but also time then there is a high likelihood that the network will appear as a single connected component. So while at any given instant, the network may not be connected, it may still be possible to route data from a source to a destination. DTNs are sometimes also called Intermittently-Connected Mobile Networks (ICMNs). The primary goal in such networks is to get the information from a source to the destination; these networks can tolerate a relatively higher delay. A wide variety of ”challenged” networks fall under this category ranging from outer-space networks, under-water networks, wireless sensor networks, vehicular networks, sparse mobile ad-hoc networks etc. Students moving about in a college campus (Hsu & Helmy (2006)), or buses moving about in a small metropolitan area (Burgess et al. (2006)), or a wireless sensor network with some mobile nodes (Shah et al. (2003); Juang et al. (2002)) acting as relays to assist in the data-collection phase provide representative examples of DTNs. This chapter strives to provide a survey of some of the most relevant studies that have appeared in the domain of data delivery in delay tolerant networks. First, we introduce some fundamental challenges that are unique to DTNs. Then we present the major parameters of interest that various proposed routing solutions have considered, examples include end-to-end delay, throughput, mobility model of the nodes, energy efficiency, storage etc. Subsequently, we provide a classification of various approaches to routing in DTNs and pigeon-hole the major studies that have appeared in the last few years into the classified categories.