Interplanetary Internet (IPN),

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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.

Evolving Wireless Networks Outside the Internet
Communication outside of the Internet—where power-limited mobile wireless, satellite, and interplanetary communications are developing—is accomplished on independent networks, each supporting specialized communication requirements. These networks do not use Internet protocols and they are mutually incompatible —each is good at passing messages within its network, but not able to exchange messages between networks. Each network is adapted to a particular communication region, in which communication characteristics are relatively homogeneous.


The Concept of a Delay-Tolerant Network (DTN)
A delay-tolerant network (DTN) is a network of regional networks. It is an overlay on top of regional networks, including the Internet.
DTNs support interoperability of regional networks by accommodating long delays between and within regional networks, and by translating between regional network communication characteristics. In providing these functions,

Today’s Internet—Packet Switching
Communication on the Internet is based on packet switching. Packets are pieces of a complete block of user data (e.g., pieces of an email message or a web page) that travel independently from source to destination through a network of links connected by routers. The source, destination, and routers are collectively called nodes.Each packet that makes up a message can take a different path through the network.