The Disruption Tolerant Networking (DTN) program establishes a long-term, readily accessible communications test-bed onboard the International Space Station (ISS). Two Commercial Generic Bioprocessing Apparatus (CGBA), CGBA-5 and CGBA-4, will serve as communications test computers that transmit messages between ISS and ground Mission Control Centers. All data will be monitored and controlled at the BioServe remote Payload Operations Control Center (POCC) located on the Engineering Center premises at the University of Colorado – Boulder.
The Office of Space Communications and Navigation (SCaN) at NASA Headquarters leads the Delay Tolerant Networking (DTN) investigation with the goal of advancing the maturity and heritage (space flight use) of the DTN communication protocols. Delay tolerant networks make use of store-and-forward techniques within the network in order to compensate for intermittent link connectivity. In the DTN the fundamental concept is an architecture based on Internet-independent middleware where protocols at all layers are used that best suit the operation within each environment, with a new overlay network protocol (bundle protocol) inserted between the applications and the locally optimized communications stacks. Many applications can benefit from the reliable delivery of messages in a disconnected network.?? The internet, in contrast, is a connected network where internet protocols, most notably transmission control protocol/internet protocol (TCP/IP), are dependent upon (low) latencies of approximately milliseconds. This low latency, coupled with low bit error rates (BER), allows TCP to reliably transmit and receive acknowledgements for messages traversing the terrestrial Internet. One of the best examples of high latency, high BER links, with intermittent connectivity is that of space communications. One-way trip times, at the speed of light, from the Earth to the moon incurs a delay of 1.7 seconds; while one-way trip times to Mars incur a minimum delay of 8 minutes. The problem of latency for interplanetary links is exasperated with increased BER due to solar radiation. In addition, the celestial bodies are in constant motion, which can block the required line-of-sight between transmit and receive antennas, resulting in links that at best are only intermittently connected. Intermittent link connectivity is commonplace terrestrially as well. One example is the plethora of battery-powered mobile communications devices that go in and out of communication range to wired service interface points and are turned on and off at the users discretion.