"Just as you can communicate on Earth without the Internet, you could build such a space base without DTN, but its communications systems would be very expensive and unreliable, since there would be lots of custom and manual capabilities required that are already fully standardized by DTN," Hooke wrote in an email interview.
NASA has been working on DTN "in earnest" since 2000, according to Hooke. A key proponent of the technology is Vint Cerf, one of the founders of the current Internet. It has used the system successfully to transmit data through space. In the latest experiment, ISS commander Williams controlled the Earthbound robot in Darmstadt, Germany, for about 90 minutes and exchanged data with it. The network connection between the robot and the ISS, more than 200 miles above Earth, delivered 50 kilobytes per second down and 82 bytes per second up. Data took seven seconds to make the round trip.
The agency expects to be able to use DTN on missions that will launch around 2015. But the technology may also have more down-to-Earth applications. Because it's designed to handle intermittent link connectivity, or communication without a constant connection, it could be useful for military networks or for using any type of battery-powered mobile communications device that goes in and out of range of a network, NASA says.
There is no limit to how far DTN could go. "There are no limits -- DTN could run into interstellar space," Hooke wrote. "It's more a question of how long the user can wait for a response."
However, the hop-by-hop nature of DTN would require some nodes along the way. These could be supplied by spacecraft purpose-built as relays or by older craft that had already fulfilled their original purposes, according to Hooke.
The "Interplanetary Internet" that NASA envisions might be a network of networks all built on DTN, but with two sets of standard protocols.
"DTN can run over the terrestrial Internet protocols in small areas of space where the communications environment is a lot like that on Earth. However, the performance of the Internet protocols rapidly breaks down in long-delay or disrupted environments, so DTN will be the end-to-end protocol, traversing local "islands of IP" along the path," he wrote.