Routing Around the Obstacles
DARPA Tests Battlefield Alternative To IP Comms
Beneath America's multibillion-dollar push to deliver wireless Internet protocol (IP) communications to the battlefield lurks a problem: Such networks require unobstructed pathways between sender and recipient. Jamming, poor weather, power outages or obstructions can cut vital links.
"IP works in the command parts of the Army, Navy and Air Force, but there is still that last tactical mile where IP-based communications are a challenge," said retired Army Lt. Gen. Peter Cuviello, a former Army chief information officer and now managing director of BearingPoint, a consulting firm in Virginia. "Where the infantryman is roaming is low-bandwidth. Until we can get a bigger pipe in a smaller radius down to the infantry, IP is going to stop at the battalion command post."
Now experts at the U.S. Defense Advanced Research Projects Agency (DARPA) are testing a NASA-pioneered messaging software called Disruption Tolerant Networking (DTN), which would use a more flexible addressing format to automatically route messages around disruptions. The concept uses mobile relay nodes, possibly UAVs circling overhead.
DARPA plans to test the DTN concept in May under its Wireless Network After Next program, in which engineers want to see if they can use inexpensive tactical radios as relay nodes.
Think of a basketball game, said Adrian Hooke, NASA's manager for space-networking architecture. When a player's path to the hoop is obstructed, he passes the ball. Eventually, if all goes well, it gets to the hoop.
NASA hopes to use DTN to command deep-space probes and bounce pictures of planets and foreign moons back to Earth using relay spacecraft. U.S. military commanders might someday rely on it to beam intelligence and battle plans to troops under fire, when disruptions are most likely and new information most necessary.
"As you move out into this chaotic, unpredictable environment, you have got to rethink networking and deal with disruption not as a rare case, which it might be for an Internet service provider, but as the norm," said Preston Marshall, DARPA's DTN program manager.
Early Test
DARPA program managers first ran the DTN concept through a field test in 2007. In a three-week exercise involving 20 DTN nodes at Fort A.P. Hill, Va., soldiers transmitted information about a mock roadside bomb attack wirelessly to another unit about two kilometers away. Sport utility vehicles equipped with computers and radios stood in for the UAVs that might someday act as mobile relay nodes.
"Each node was able to hand data to any other node it came in contact with, so we were able to route data even when there was no immediate path," said Jason Redi, principal scientist for BBN Technologies of Cambridge, Mass., the company that developed the prototype DTN system for DARPA.
DTN was also able to deliver information to specific users and groups, such as all company commanders, Redi said.
In August, DARPA awarded BBN an $8.9 million contract to explore how DTN might be used with existing military communications equipment.
"We are still talking to all the stakeholders to find out what they need to see to make a decision about deploying the technology," DARPA's Marshall said.
Later this year, BBN engineers and scientists plan to conduct a trial with up to hundreds of DTN nodes.
Even DTN's most enthusiastic supporters decline to predict when DTN could become a standard feature of military communications.
"We spent a lot of time getting IP everywhere," Marshall said. "Now it's time to think about the things IP doesn't do well and how to address them."
Ad-hoc networking solves problems, but it also creates a new one.
"Security gets more interesting with DTN because now the data may live on intermediate nodes for longer periods of time than in normal situations," Redi said.
To improve security, DTN developers are planning to link classified messages sent through communication networks with unclassified data, such as routing information and a description of the message's contents.
That unclassified data will enable the message to travel through the network and reach its intended recipients, who alone will hold the cryptographic key needed to read the classified portion.
Solution to an Old Problem?
If this works, it might actually solve a problem of older vintage: how to use a single network to send information of different classification levels, Marshall said. This would be particularly useful for military units operating alongside coalition partners.
"We would like to show in the next demonstration that we can build ... servers that provide content to nodes and never actually read the content they are providing," Marshall said.
Managers of the Wireless Network After Next program hope to link hundreds or thousands of $500 tactical radios into a network that would constantly reshape itself to cope with disruptions.
DTN cannot solve every problem. It isn't appropriate for voice service, for example.
"If I say, 'Come here,' I don't want that message ... played an hour from now," Redi said. "Those kinds of messages will be delivered if we have an immediate path."
Forces would rely on DTN for situational awareness. Even if someone joins the network an hour after an enemy location has been spotted, that information still will be useful to them, Redi added.
DTN advocates are not downplaying the challenges that remain.
"We know it is going to be very difficult to run a network with 100,000 things connecting and disconnecting," Marshall said.
Advocates plan to keep pushing for more demonstrations of the technology.
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