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New coding would shape future generation networks

Published by under Communications,News categories on May 30, 2008

Blue light beam spreading Network coding, a novel wireless-network protocol developed for the U.S. army, breaks the rules by sending not the data itself but rather a description of the data. In simulations, a network using the protocol was five times more efficient than a traditional network. Within the next year, the U.S. Defense Advanced Research Projects Agency (DARPA) will test the protocol in field trials.

The protocol is part of a project to create a new generation of mobile ad-hoc networks–self-configuring networks of mobile wireless nodes–that will enable faster and more reliable tactical communications between military personnel and vehicles, But the project also demonstrates the potential of the new exciting field called network coding .

In a traditional network, you break information into packets and forward them between nodes. If a packet doesn’t reach its destination, it will be sent and re-sent until its arrival is confirmed. But in some types of network, such as mobile wireless networks, there is a fairly high chance that the packets won’t be received because of interference or limited bandwidth, or because a mobile node has wandered out of range or been destroyed. If nodes keep transmitting data until they receive confirmation, a bottleneck can result.

With network coding this is not an issue. You take a group of packets and combine them. The result is a single packet that contains traces of information from each of the original packets. This hybrid packet is then sent to one or more additional nodes.

By itself, the hybrid packet just looks like gobbledegook. But it includes a small amount of data that acts as a clue to its contents. A single packet won’t normally contain enough clues to allow its data to be reconstructed. But as long as the destination node receives enough independent packets from enough different sources, it should be able to recover all the original data.

The advantage of this is not only that you are using less bandwidth to send information, and thus avoiding bottlenecks, but also that you don’t have to keep track of which node sent what.

Surprisingly, even the means of combining data into a single packet at the source node doesn’t have to be shared. If the packets contain enough clues, the destination nodes can reconstruct the contents of packets that have been created randomly. You’re not sending data, you’re sending pieces of algorithms for assembling data.

Network coding is an offshoot of a field called information theory, which has already been put to use in data-compression software. But it’s only relatively recently that people have started looking at how network coding could be used to send data. It turns out it can be extremely powerful.

As part of a program funded by DARPA, BAE and MIT (Last news from MIT) used network-coding principles to develop protocols that could be used to send information to multiple destinations. In a conventional network, each node would act like a router, steering specific information toward specific destinations. But in BAE and DARPA’s network, all nodes broadcast all information to all other nodes.

In the DARPA simulations, where a tactical mobile network was emulated on an Ethernet network, the researchers experimented to see how much they could reduce the bandwidth of the network while maintaining the same standard of communication. The simulations involved all forms of military data, from voice and video streams to tactical data, and all kinds of conditions, such as interference and poor connectivity.

The researchers found that they could reduce the bandwidth to just one-fifth of that required by a conventional network, with no loss of quality. The upcoming field tests, on the other hand, will investigate whether the protocols can be used to send more data over existing radio networks than standard protocols can.


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