Virtually Delayed: An investigation into delay tolerant networks and their emulation in a virtual environment

Tomlinson, Paul N. (2009). Virtually Delayed: An investigation into delay tolerant networks and their emulation in a virtual environment. Student dissertation for The Open University module M801 MSc in Software Development Research Dissertation.

Please note that this student dissertation is made available in the format that it was submitted for examination, thus the author has not been able to correct errors and/or departures from academic standards in areas such as referencing.



Delay tolerant networking (DTN) offers a novel way to successfully transfer information over severely delayed, disrupted or periodically disconnected networks. Such delays or disruption would either cause the transmission control protocol (TCP) to fail or perform extremely poorly. The research presented here shows the creation of a virtualised test environment, including a channel emulator, which was used to show the effects of delays and errors on both TCP and two DTN implementations. The breakdown of two variants of TCP under increasing delay was shown with TCP Hybla performing much better than the default TCP Reno. The theoretical and actual performance of TCP’s retransmission timeouts was also investigated. In tests retransmission timings neither corresponded to those used by simulation software nor matched the assumptions made in some other research. The test environment was next used to perform experiments on the DTN2 Reference implementation and Interplanetary Overlay Network. These were run over both TCP and UDP and as expected show resilience and better performance as delays are increased. Some issues were found with DTN2 running over UDP. However, ION running the Licklider Transmission Protocol showed the ability to successfully transfer an image file over delays representing the distance, in terms of light-seconds, between Mars and the Earth using the Moon as a router. When the same transfer was attempted using FTP over TCP it was a total failure despite making adjustments to timing and retry settings in both FTP and TCP. A comprehensive literature review provides an up to date insight into DTN's short history, the state of current research and those areas that still need addressing or where debate exists.

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