Opportunistic and Delay-Tolerant Networks
EURASIP Journal on Wireless Communications and Networking
Today, people predominately rely on the Internet and cellular network, as well as the plain old telephone system, to communicate with each other. Typically, these communication services are built from fixed wired or wireless infrastructure, where the "next hop" is known in advance, well engineered and its performance in terms of delay, throughput, and loss characteristics has been well studied. Over the last decade, a new paradigm in end-to-end communications has emerged, mostly in academia and
... tly in academia and industrial research laboratories, based on the notion that the next hop between a sender and receiver is not known in advance. These networks, typically called opportunistic and delay-tolerant networks, are characterized as opportunistic because, like nodes in mobile ad hoc networking infrastructure, the forwarding nodes are mobile and dynamic-they come and go in unpredictable ways. In this case, it is very hard to make strong statements about the type of service opportunistic networks will offer the user. Opportunistic nodes collectively form dynamic networks that are built from short unpredictable contact times as nodes move in and out of connectivity. Unlike mobile ad hoc networks, which aim to offer a frequently available connected path through a dynamic network, opportunistic networks only offer a store and forward service in a mostly disconnected network comprised of infrequent contact times between nodes-therefore, these networks aim to find the next "storage node" toward the destination as a primary communications service. Because of this, most applications have to be delay tolerant in nature, hence the name: opportunistic and delay-tolerant networks. Many applications of opportunistic and delay-tolerant networks are being actively studied, for example, networks purely comprised of people carrying devices that only use short range radios, wildlife-based mobile low-power sensor networks, and interplanetary networks. While this new form of communication has created great interest in the research community, it is still in its infancy in terms of emerging communications architectures, algorithms, protocols, tools, modeling, and standards. As yet there has been "no killer app" that has emerged other than the grand challenge of interplanetary communications or niche deployments in sensor networks or mobile human-centric experimental networks. However, these networks show great promise in terms of their fully decentralized design making them extremely robust. They also offer the potential for huge bandwidth gains in contrast to other forms of networks (e.g., MANETs or the existing cellular network) but at the cost of higher end-to-end delays. The duality of higher bandwidth gains over short-lived next-hop connections and longer end-to-end delays, coupled with the spontaneous creation of dynamic networks, has captured the imagination of networking researchers. The papers in this special issue, which was promoted under the auspices of the EC-funded Network of Excellence in Wireless Communications (in particular, the Work Package WPR.11 on Opportunistic Networks), address a number of the issues and challenges discussed above. We received a total of 23 high-quality submissions. The papers came from different regions around the world and addressed many different aspects of research. Each paper was reviewed by three or more experts, who evaluated the technical content and suitability of the paper for publication in this special issue. As Guest Editors of the special issue we had the very difficult job of selecting only 10 papers from those submitted. The papers of this special issue cover both practical and theoretical aspects of opportunistic and delay-tolerant networking.