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Marines Get the Data Despite Disruptions May 2007
One of the most significant problems of modern warfare is that our warfighters can outrun their communications infrastructure. For instance, when the U.S. Marine Corps moved from Kuwait up to Baghdad during the early stages of Operation Iraqi Freedom in 2003, they quickly overran their line-of-sight radio links and had to rely on commercial satellites to keep in contact with their widely dispersed units. But what could be done about it? Eventually, the Marines will use the still-in-development Joint Tactical Radio System to communicate. In the meantime, the Marines are using an air conditioned case of equipment in the back of a Humvee. The equipment is called a Command and Control on the Move Network, Digital Over the Horizon Relay (CONDOR), a system that includes routers, cryptographic equipment, a ground radio, and a satellite modem. But even with satellite communications, CONDOR isn't foolproof. It can lose connection with the satellite because of pitching around on rough roads or because trees or buildings block the view. To increase CONDOR's reliability, MITRE designed a solution that originally went beyond tough terrain and literally into outer space. It's called disruption-tolerant networking (DTN) and was first designed for communicating with spacecraft to compensate for disconnections over interplanetary distances. "There can be a delay of 8 to 40 minutes for a round-trip signal to Mars," says Robert Durst, a senior principal network and communications engineer at MITRE. "With delays so extreme, the interplanetary-Internet model forced us to think about communications differently. That model works very well in a tactical environment." No Do-Overs Necessary By adding DTN to CONDOR, the Marines can be sure their intended recipients eventually get the whole message. "Disruptive communication has effects that persist far beyond the period when you're disconnected from the satellite," explains Durst. "Disconnection causes the Marine Corps databases to become de-synchronized. The re-synchronization process is painful because disconnection can cause a 'start over' process." DTN avoids re-synchronization and provides a "store-and-forward" mechanism for messages within the network. "Even if you lose sight of the satellite and become disconnected, the data is stored for you," says Durst. "As soon as you get satellite connectivity back, data flows as if it weren't lost. The original data gets to you eventually." DTN for CONDOR helps the Marines with problems such as host and router mobility, terrain and environmental interference, intentional interference like jamming, intermittent connectivity, lower data rates, and long latency. The "store-and-forward" mechanism is an overlay protocol that uses existing networks so that DTN can aid in building a heterogeneous system and aid joint application interoperability. Persistence and Custody "DTN breaks an end-to-end transfer into a sequence of reliable and persistently stored message transfers," says Durst. "Information that was previously lost due to network disruption is now preserved. The message is retransmitted from an in-network point close to the point of disruption, instead of having to be retransmitted from the original source at the edge of the tactical network." The reliability of DTN depends on custody transfers between DTN routers. Each DTN message marked for reliable delivery has a custodian (in the form of software) whose job is to make sure that the message reaches the destination. As the message flows through the overlay network, custody can be transferred from one DTN router to another. This way, the message and responsibility for the message moves progressively towards its destination. "DTN will be particularly useful for things like chat, email, and the common operational picture," says Durst. "For example, battle management and coordinating with different commanders in the field are often done with instant messaging. We have built an Internet relay chat server that runs over DTN. If you've been off the network for a while, it gets the stuff that went on while you were away and displays it to you, but it's marked as being old." Four Designs Durst and his associates have come up with three hardware designs and one software design for adding DTN to CONDOR. The first is a Cisco Intrusion Detection System (CIDS), which has software called Application-Oriented Networking. "It's basically a Linux computer with a large disk that plugs into the existing CONDOR Cisco router. While this would work, it is tied to the current design, which we know will change." The second design is a computer box with a square 5-in. by 5-in. cross section that's 6-in. long. It's built using the PC-104 format, which is a compact board that has low power consumption and can be stacked to save space. The unit is passively cooled with fins, which simplifies the design and avoids tapping into the CONDOR's air conditioning. It's also sealed against blowing dust and runs on 9-60 volts DC. The third design uses the PC-104 cards from the second design and integrates them with a Cisco Mobile Router, also with a PC-104 form factor. Like the second unit, it's passively cooled. The fourth design uses EMC's VMware to host the DTN software on a virtual Linux host that runs as an application within the CONDOR unit's existing Windows laptop. This eliminates hardware additions from the system entirely, because the virtualization process creates a "computer within a computer" that operates separately from the rest of the machinery, but within the same box. While there are other issues of blending DTN into CONDOR, Durst and his colleagues believe that DTN will improve the tactical environment for the Marines until and beyond the arrival of the next generation technologies like JTRS. "We're giving the Marines a simple solution for their interim system," says Durst. "When they put it into operation, they won't have to worry about outrunning their communications infrastructure." Even when JTRS arrives, the situations that motivate the use of DTN will still occur. DTN provides a robust networking capability for both the near- and long-term. —by David A. Van Cleave Solving the problems of the Marine's DTN system for CONDOR took a team of MITRE employees that included Bob Durst, Susan Symington, Salil Parikh, and Keith Scott. Related Information Articles and News
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