[CMC] Disruption-tolerant nets set for large-scale test

[Adrian J. Hooke]

http://www.networkworld.com/news/2008/082208-dtn-networks.html?fsrc=netflash-rss

Disruption-tolerant nets set for large-scale test

Phase 3 of DARPA project will demonstrate a large-scale DTN in the field
By John Cox , Network World , 08/22/2008

Scientists at BBN Technologies have begun readying a large-scale 
field test of a mobile network designed to keep working despite 
transmission failures, glitches and long delays.

The test is the third phase of a Department of Defense project to 
create disruption-tolerant networks, or DTNs. It builds on a field 
prototype of 20 nodes that was successfully demonstrated last 
November at the Army's Fort A.P. Hill in Virginia. The large-scale 
trial, due in late 2009, is intended to show that big DTNs are not 
only possible, but also commercially viable and able to be built with 
off-the-shelf, standard components.
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To fund Phase 3, the Defense Department's Defense Advanced Research 
Projects Agency (DARPA) just awarded almost $9 million to BBN. Key 
priorities involve work on DTN scalability and robustness to support 
thousands of nodes, and designing and implementing new algorithms for 
several key tasks. The BBN team also will be working with the U.S. 
Marines to introduce DTN into the Marines' CONDOR mobile network 
program, which is designed to link maneuvering units with command 
centers beyond line-of-sight (about 20 to 30 miles).

Though driven by military networking requirements, DTNs potentially 
have a much wider applicability. They can sustain communications 
without the stability, connectivity and predictability required by 
today's IP networks, including the Internet. If these networks lose a 
connection or suffer delays, packet deliveries plummet because the 
existing routing protocols assume an end-to-end path that becomes 
stable fairly quickly. But those assumptions break down in the face 
of repeated disconnections and long delays, which can be caused by 
equipment failures, weather, terrain or jamming.

One civilian prototype is the DieselNet project at the University of 
Massachusetts-Amherst. DieselNet consists of off-the-shelf 
single-board computers, GPS receivers and radios mounted in 40 UMass 
buses. As two buses near each other, their DTN nodes query each other 
to find out what other nodes each sees most frequently. If one of 
those other nodes is related to the final network destination of a 
message, that message is handed off to the passing node in the 
seconds they're close enough for the Wi-Fi connection. At some point, 
the message is handed to a node attached to the wired Internet.

Central to DTN's effectiveness is the technology's tenacity. "IP 
networks have as a philosophy the idea [that] 'if there's a problem, 
give up. The user will resend.' DTN doesn't give up. It's constantly 
trying to move the information forward," says Christopher Small, 
senior scientist with the Networking Research Group at BBN's 
Cambridge, Mass., headquarters. "DTN will work around breaks, and 
route the information any way it can."

That tenacity is due in large part to a new BBN-written routing 
protocol, called Bundle, which makes use of queuing and other 
techniques, including one called late binding. With late binding, a 
source node in a DTN can send a message even though the final 
destination IP address can't be known due to disruptions of name 
servers or routers. It's sort of like mailing an envelope that has 
blank spaces in the address.

As the packet makes its way through the DTN, this additional 
information gets filled in. Eventually, the destination IP address 
binding takes place, and the transmission completes as the packet is 
forwarded by any available connection.

The three-week prototype field test at Fort A.P. Hill last fall 
involved 20 nodes, mainly laptop-like embedded computers, running the 
DTN protocol with GPS and Wi-Fi connectivity [see photograph]. Most 
of the nodes were stationary, representing soldiers at a simulated 
forward operations base, trying to communicate with a headquarters 
site about 2 kilometers away. The scenario simulated sending back 
tactical information (such as ammunition levels and enemy sightings) 
so that headquarters staff could form an accurate, timely view of the 
forward base's status.

Several of the nodes were mounted in SUVs which drove a periodic 
circuit between the two locations. The vehicles were simulating 
airborne drones that could circle over the locations with a wireless 
link to the ground nodes.

Alongside the DTN was a standard IP network; each packet was 
transmitted over both networks to compare performance.

The difference was dramatic, according to Small. The DTN network was 
able to successfully transmit five times the amount of status 
information as the IP network.

The nodes representing soldiers were able to queue their 
transmissions, then hand them off to nodes mounted on the moving 
trucks. When the truck nodes came in range of a headquarters node, 
the transmission was successfully completed.

Now it's time to up the ante.

"This is where it gets interesting," Small says. "We're not going to 
deploy this with 100,000 troops [in this phase], but we will 
demonstrate that it can work with hundreds of nodes, and that it can 
work for weeks at a time."

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