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Introduction
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, which must encompass both terrestrial and interplanetary links, is an extreme case. An architecture based on a "least common denominator" protocol that can operate successfully and (where required) reliably in multiple disparate environments would simplify the development and deployment of such applications. The highly successful architecture and supporting protocols of today's Internet are ill suited for this purpose. But Delay Tolerant Networking will crossover this bottle-neck. In this seminar the fundamental principles that would underlie a delay-tolerant networking (DTN) architecture and the main structural elements of that architecture, centered on a new end-to-end overlay network protocol called Bundling is examined.

The US Defense Advanced Research Projects Agency (DARPA), as part of its "Next Generation Internet" initiative, has recently been supporting a small group at the Jet Propulsion Laboratory (JPL) in Pasadena, California to study the technical architecture of an "Interplanetary Internet". The idea was to blend ongoing work in standardized space communications capabilities with state of the art techniques being developed within the terrestrial Internet community, with a goal of facilitating a transition as the Earth's Internet moves off-planet. The "Interplanetary Internet" name was deliberately coined to suggest a far-future integration of space and terrestrial
communications infrastructure to support the migration of human intelligence throughout the Solar System. Joining the JPL team in this work was one of the original designers of the Internet and co-inventor of the "Transmission Control Protocol/Internet Protocol" (TCP/IP) protocol suite. Support for the work has recently transitioned from DARPA to NASA.

An architecture based on a "least common denominator " protocol that can operate successfully and reliably in multiple disparate environments would simplify the development and deployment of Interplanetary Internet. It is this analysis that lead to the proposal of Delay-Tolerant Network (DTN) architecture, an architecture that can support deep space applications, centered on a new end-to-end overlay network protocol called 'Bundling'. The architecture and protocols developed for the project could also be useful in terrestrial environments where the dependence on real time interactive communication is not possible. The Internet protocols are ill suited for this purpose, while the overlay protocol used in DTN architecture serves to bridge between different stacks at the boundaries between environments in a standard manner, in effect providing a general -purpose application-level gateway infrastructure that can be used by any number of applications. DTN is 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.

Research on extending Earth's Internet into interplanetary space has been underway for several years as part of an international communications standardization body known as the Consultative Committee for Space Data Systems (CCSDS).

CCSDS is primarily concerned with communications standards for scientific satellites, with a focus more on the needs of near-term missions. To extend this horizon into the future, and to involve the terrestrial internet research and engineering communities, a special Interplanetary Internet study was proposed and subsequently sponsored in the United States by NASA's Jet Propulsion Laboratory (JPL) and DARPA's Next Generation Internet Initiative

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