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by Elwyn Davies
DTN research started a little over ten years ago when Vint Cerf and colleagues started examining what would be needed to extend the burgeoning Internet beyond the confines of Planet Earth coining the phrase Interplanetary Internet. During this time the initiative has continued to push back the boundaries into space but has also come back down to earth first as Delay-Tolerant Networking and then as Delay- and Disruption-Tolerant Networking.
The primary aim of N4C is to demonstrate that Delay- and Disruption-Tolerant Networking (DTN) can extend the 'broadband' Internet experience to users living in or visiting communities that are unlikely to be served by the conventional infrastructure that delivers high-bandwidth connectivity to more densely populated regions. We call these areas communications challenged communities, and the challenge is usually driven by the economics of sparsely populated regions exacerbated by environmental issues. Installing the infrastructure in these communities is expensive and the return on investment is likely to be low.
N4C will concentrate on building a system which requires very little permanently installed equipment and uses predominantly low end, commodity equipment so that potential users can get the benefits without a lot of investment and with low running costs - the decision to participate should be an ?impulse purchase' rather than a major investment decision. This is very important to the N4C concept because we want the user to be the network; so the network will be better the more users participate.
But it will only work really well if many of the users (and hence the network) are nomadic. We need the users to move around and encounter others - a population of hermits will not be useful! We want these users to be able to have an experience with applications that is as compelling as the one that has driven the explosive growth of the conventional Internet, so that they will be able to use it to support business, education and leisure in the communications challenged areas without forcing unwelcome cultural changes on the users. Achieving this means that the N4C system needs to be well-integrated with the conventional Internet and provides applications that are well-adapted to the DTN environment and manage human expectations to avoid provoking frustrations when responses are not instant.
Major assumptions of the existing Internet are that messages need only be stored transiently and communications along the forwarding path are relatively rarely disrupted or interrupted. DTN seeks to provide usable Internet-style communications even where the delay between transmission and reception or request and response at the end points of the communication is far greater than either would be acceptable to the humans using today's applications or feasible using today's communication protocols. It also aims to facilitate communication where there is no guarantee that messages can be forwarded 'immediately' upon arrival at an intermediate waypoint, such as a router.
DTN stands at a crossroads because to date much, although not all, research has concentrated on a building an 'overlay' transport network that can transfer files or bundles from place to place without worrying too much about how this capability would integrate with applications that humans would find useful and without being overly concerned with integrating DTN capabilities with the existing Internet. To show that DTN is a useful technology to extend the Internet into communication challenged regions, we need both to make the infrastructure robust and design applications that provide useful, secure capabilities for business, education and leisure when running over a combined DTN and existing Internet infrastructure.
Succeeding with this aim goes beyond providing a niche solution applicable to a small portion of the population, however technically, socially and culturally laudable this aim may be. The steady growth of the conventional Internet and the growing complexity of both applications and the network infrastructure tends to come at a price: while the bits may travel end to end at near light speed, the responses seen by humans and applications at the end points may be subject to significant delay, because of additional computing, message round trips, setup delays and authorization requirements that result from added complexity in networks and applications. Applications today often behave in a very user unfriendly manner when the underlying network does not exhibit low delay, reliable connectivity.
DTN, as a whole, can be seen as a tool to help adapt applications to networks with long or variable delays and intermittent connectivity, but it will also be essential to adapt applications to manage human expectations to ensure that the human user doesn't feel that s/he is responsible for the ?failings' of the network. This kind of adaptation needs to become mainstream and DTN-oriented research such as N4C ought to provide insights that will be applicable across the whole network environment of the future.
The founder of N4C partner Folly Consulting Ltd, Elwyn Davies, has been involved with Delay- and Disruption-Tolerant research for about five years. Before N4C started, Elwyn was a volunteer in the Sámi Networking Connectivity (SNC) project, assisting with software development and looking at web caching applications.
Before becoming fully committed to DTN work, Elwyn had spent almost 20 years working first with applications using the conventional Internet protocols for communication and since 1998 working on the protocols themselves with Nortel Networks. Elwyn has been a regular participant in the IETF standards organization
since 1998, working on the Differentiated Services Quality of Service architecture and more recently on network signalling (NSIS) and IPv6. After taking early retirement from Nortel in 2004, Elwyn was appointed to the Internet Architecture Board of the IETF for a two year term.
