Delay Tolerant Networks

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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.

Today?s Internet
The Internet has been a great success at interconnecting communication devices across the globe. It has done this by using a homogeneous set of communication protocols, called the TCP/IP protocol suite. All devices on the hundreds of thousands of subnets that make up the Internet use these protocols for routing data and insuring the reliability of message exchanges.
Connectivity on the Internet relies primarily on wired links, including the wired telephone network, although new wireless technologies such as short-range mobile and satellite links are beginning to appear. These links are continuously connected in end-to-end, low-delay paths between sources and destinations.They have low error rates and relatively symmetric bidirectional data rates.

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