New Internet for Space, New Technologies to Test - Disruption-Tolerant Networking (DTN)
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This new testing of DTN technology and software has recently and successfully allowed NASA researchers to send and receive dozens of deep space images at a test distance of around 20 million miles from Earth. DTN addresses the problem of communicating from the deepest reaches and most challenging environments possible. The fight revolves around networks where frequent and long-lasting disruptions are common.
The goal has always been to find ways to use instruments, ships, satellites and other devices as nodes, with the benefits of clear communication and a percentage of independence and autonomy. NASA sent simulated images of the Martian moon Phobos using DTN; these images were successfully transmitted back, showing how reliable and robust this technology can be.
Having just finished a month-long series of DTN testing, data was transmitted using NASAís existing Deep Space Network at a period of twice weekly. Harnessing the NASA Epoxi spacecraft, currently on a mission to find Comet Hartley 2 in less than two years, NASA was able to harness one node for this testing. This Epoxi node is currently simulating a communications relay platform in a Mars orbit. Combining it with the other nine nodes, located at the NASA Jet Propulsion Laboratory in Pasadena, CA, allows the ability to simulate Mars landings, orbiters and ground operations centers.
Typically, at a ground level (terrestrial, non-space), we use the four-decade-old technology called Transmission-Control Protocol/Internet Protocol (TCP/IP) that expects a continuous point-to-point connection. DTN, however, recognizing issues such as planetary blocking, rotational distances, power outages or solar storms, are more geared toward expecting delays, and patiently waiting for the delivery of data. The primary reason for delays is that the Earthís rotation causes data delivery from deep space to adjust for constant changing of position, for both senders and receivers of data. When combined with the vast distances over which this data is being sent, and the need for nodes to store data for an undetermined period of time, DTN has shown great promise in early testing.
Unlike TCP/IP, where data packets are commonly discarded when a destination path canít be found, a DTNís network nodes are set to store data as long as necessary, until proper communication with another node is at hand. So while send times are longer, data delivery is not the issue, according to recent, successful testing. Sending data from Mars, for example, takes between three and 20 total minutes, while traveling at the speed of light (186,000 miles per second). This new and unique approach not only uses a different methodology, but was designed to be far less cumbersome and much more resilient to disruption.
If a DTN router is required to store data for an extended period of time to complete the delivery process, the amount of storage depends on the maximum length of time and the difference between incoming and outgoing data rates. The actual technology used is an overlay methodology that could include IPv4 or IPv6 spaces. Explanations consist of DTN being based on a completely new model, called Bundle Protocol, that operates as one overlay protocol linking together multiple subnets such as LANs, Bluetooth, 802.11 WLAN and Ethernet into one single network.
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