Delay Tolerant Networking

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Consider a scientist who is responsible for the operation of robotic meteorological station located on the planet Mars (Fig. 1). The weather station is one of several dozen instrument platforms that communicate among themselves via a wireless local area network deployed on the Martian surface. The scientist wants to upgrade the software in the weather station?s data management computer by installing and dynamically loading a large new module. The module must be transmitted first from the scientist?s workstation to a deep space antenna complex, then form the antenna complex to a constellation of relay satellites in low Mars orbit (no one of which is visible from Earth ling enough on any single orbit to receive the entire module), and finally from the relay satellites to the weather station.

The first leg of this journey would typically be completed using the TCP/IP protocol suite over the Internet, where electronic communication is generally characterized by:

? Relatively small signal propagation latencies (on the order of milliseconds)
? Relatively high data rates (up to 40 Gb/s for OC-768 service)
? Bidirectional communication on each connection
? Continuous end-to-end connectivity
? On-demand network access with high potential for congestion

However, for the second leg a different protocol stack would be necessary. Electronic communication between a tracking station and a robotic spacecraft in deep space is generally characterized by:

? Very large signal propagation latencies (on the order of minutes; Fig. 2)
? Relatively low data rates (typically 8-256 kb/s)
? Possibly time-disjoint periods of reception and transmission, due to orbital mechanics and/or spacecraft operational policy
? Intermittent scheduled connectivity
? Centrally managed access to the communication channel with essentially no potential for congestion

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