The Bundle Protocol is used to send application data across a DTN network. Originally DTN stood for Delay Tolerant Networking (lately it has been referred to as Disruption Tolerant Networking). Sometimes it is written as Delay/Disruption Tolerant Networking. In a DTN network there may be frequent Disruptions or long Delays in the connection between the network devices. Using a Store and Forward technique, application data is bundled together and stored locally at each node and then forwarded to the next node when access is available.
Wikipedia has an interesting article about The History of The Internet. There is an interesting article from How Stuff Works that shows how the Internet works and the (OSI) Open Systems Interconnection Reference Model works. Also a video of The Internet: Then & Now.
Articles on the Bundle Protocol:
The Internet Engineering Task Force (IETF) has an interesting memo on Delay-Tolerant Networking Architecture as well as the Bundle Protocol Specification (which is the core feature of a DTN). The Bundle Protocol (BP) can work over Transmission Control Protocol (TCP). If TCP is not used at the Transmission layer of the OSI model, then Licklider Transmission Protocol (LTP) which goes over User Datagram Protocol (UDP) is used to Transmit the Bundles. Either BP/TCP or BP/LTP/UDP is used for BP transmission.
Functional Specification for DTN Infrastructure Software
Use in Space:
IOAG Space Internetworking Strategy Group (SISG) & Space Internet Architecture Group (SIAG) has Information on a Recommendation on a Strategy for Space Internetworking and also Operations Concepts for a Solar System Internetwork.