DELAY tolerant networks

Delay-Tolerant Networking (DTN) is an approach to computer network architecture that seeks to address the technical issues in mobile or extreme environments, such as deep-space, that lack continuous network connectivity.

Recently, Disruption-Tolerant Networking has become a favorable term since it applies to more situations, and this term has gained currency in the United States military and DARPA, who have funded many DTN projects. Disruption may occur because of the limits of wireless radio range, sparsity of mobile nodes, energy resources, attack, and noise.

In the 1970s, spurred by the micronization of computing, researchers began developing technology for routing between non-fixed locations of computers. While the field of ad-hoc routing was inactive throughout the 1980s, the wide-spread use of wireless protocols reinvigorated the field in the 1990s as mobile ad-hoc routing and vehicular ad-hoc networking became areas of increasing interest.

With the growing interest in mobile ad-hoc routing and the proposal of the Interplanetary Internet by Vint Cerf, relating to the necessity of networking technologies that can cope with the significant delays and packet corruption of deep-space communications, the 2000s brought about increased interest in DTNs, including a growing number of academic conferences on delay and disruption tolerant networking. This field saw many optimizations on classic ad-hoc and delay-tolerant networking algorithms and began to examine factors such as security, reliability, verifiability, and other areas of research that are well understood in traditional computer networking.

The ability to transport, or route, data from a source to a destination is a fundamental ability all communication networks must have. Delay and disruption-tolerant networks (DTNs), are characterized by their lack of connectivity, resulting in a lack of instantaneous end-to-end paths. In these challenging environments, popular ad hoc routing protocols such as AODV and DSR fail to establish routes. This is due to these protocols trying to first establish a complete route and then, after the route has been established, forward the actual data. However, when instantaneous end-to-end paths are difficult or impossible to establish, routing protocols must take to a "store and forward" approach, where data is incrementally moved and stored throughout the network in hopes that it will eventually reach its destination. A common technique used to maximize the probability of a message is successfully transferred is to replicate many copies of the message in hopes that one will succeed in reaching its

Increasingly, network applications must communicate with counterparts across disparate networking environments characterized by significantly different sets of physical and operational constraints; wide variations in transmission latency are particularly troublesome. The proposed Interplanetary Internet (IPN), which must encompass both terrestrial and interplanetary links, is an extreme case. An architecture based on a protocol that can operate successfully and reliably in multiple disparate environments would simplify the development and deployment of such applications.

The Internet protocols are ill suited for this purpose. They are, in general, poorly suited to operation on paths in which some of the links operate intermittently or over extremely long propagation delays. The principle problem is reliable transport, but the operations of the Internet’s routing protocols would also raise troubling issues.

It is this analysis that leads us to propose an architecture based on Internet-independent middleware: use exactly those protocols at all layers that are best suited to operation within each environment, but insert a new overlay network protocol between the applications and the locally optimized stacks. This new protocol layer, called the bundle layer, ties together the region-specific lower layers so that application programs can communicate across multiple regions.

The DTN architecture implements store-and-forward message switching.

A DTN is a network of regional networks, where a regional network is a network that is adapted to a particular communication region, wherein communication characteristics are relatively homogeneous. Thus, DTNs support interoperability of regional networks by accommodating long delays between and within regional networks, and by translating between regional communication characteristics.