Delay Tolerant Networks: A Retrospective

In order to ensure ubiquitous connectivity, networks have to operate in regions with very limited infrastructure support. There has been intense recent research activity in the emerging areas of intermittently connected, ad hoc, and delay/disruption tolerant networks (DTN). DTNs differ greatly, depending on the nature of the network environment; they range from deep space networks to buses driving around mobile wireless hotspots in villages to provide Internet service to kiosks. This has led to a wide range of solutions for routing, naming, addressing, message formats, etc. However, there are common features which have already established themselves as standards. We attempt to provide an introduction to the field of DTNs for new researchers, explaining general DTN concepts and standards, surveying the current research, and finally reviewing the available and required capabilities of DTNs so as to identify areas of future work (such as key management, handling of congestion, multicasting capability, and routing).