In much the same way that digital TV is replacing analog, a revolution is brewing in the networking industry. It is being driven by an information-transmission technology called network coding, which promises to more than double network capacities while increasing reliability and security. First proposed in 1999, network coding is now drawing the interest of large network-equipment manufacturers and software developers.
Network coding uses algebraic algorithms to represent two or more strings of data, with one derivative string called "evidence." Instead of transmitting all of the data in the original strings, one needs to transmit only the evidence. The receiving node then deduces the original information from the evidence, using rules supplied to it ahead of time or embedded in the packet that carries the evidence.
Transmitting the same information using fewer than half as many bits effectively doubles a network's capacity. In fact, the receiver needn't receive all of the evidence in order to deduce the original messages. This capability to deduce a complete message from incomplete evidence means that network coding is more reliable and resistant to attack. It doesn't matter if some bits are lost, as long as enough bits get through to enable deduction of the message.
For more technical example, let us take two strings of data. Network-coding equipment — called a coder — would perform a bitwise exclusive OR operation on each pair of bits in the two strings, assigning a value of one if the two bits (one from each string) are the same and a zero if they are different. The resulting string of ones and zeros is the evidence of two original messages.
Unlike a packet-switched network, evidence is transmitted along multiple paths simultaneously. By employing underutilized network paths, network coding increases the rate at which evidence reaches its destination.
Network coding departs sharply from the "cars-on-a-highway" model of data transportation. First, it enables a bit leaving a node to travel two paths simultaneously, something a car can't do. Second, it allows a pair of bitstreams arriving at a bottleneck to be combined (by a coder) into a single stream. Cars that meet on a narrow bridge can't do that; one must wait while the other passes.
In a traditional packet-switched network, high traffic volume often leads to bottlenecks and long delays as packets tend to bunch up at particular nodes, sometimes overwhelming the nodes' processing capabilities. Meanwhile, other routes and nodes may be underutilized.
In network coding, the receiver may combine multiple bits of evidence to deduce one packet of information. This technique tends to minimize the number and severity of bottlenecks, resulting in increased throughput and reliability.
The increase in throughput using network coding versus packet-switching depends on the volume of traffic, the network topology, and the frequency and severity of bottlenecks experienced with routing. Network coding is expected to be particularly effective with multicast networks, wireless-sensor networks, digital file distribution and P2P (peer-to-peer) file sharing, and the Internet.
Microsoft made a trial of network coding during October and November of 2007 in its Microsoft Secure Content Distribution system, which was used by customers to download a new release of Microsoft Visual Studio 2008 Beta 2. This marked the first time that Microsoft distributed Visual Studio via P2P networking. Customer feedback was positive, the company reported, and the network was easily maintained. Microsoft, like all other vendors, has not publicly acknowledged any plans for commercial products based upon network coding.
But several major players admit to playing with network coding in their labs. Cisco Systems Inc. seems particularly interested in network coding's capability to distinguish between types of data, which would have obvious quality-of-service applications. Hewlett-Packard is funding Massachusetts Institute of Technology's research into network coding with an eye on P2P networking. Intel Corp. expects network coding to benefit wireless networks, particularly WiMAX , increasing throughput by 25 to 40 percent.
Security is enhanced by network coding's very nature. The actual information is not transmitted, so it cannot be intercepted . The evidence is of no use to an eavesdropper without knowledge of how to deduce the original packets. Also, network-coding techniques can detect and stop malicious pollution attacks on a P2P network.
Network coding will not take over from routing as quickly as digital TV replaced analog. The "rack life" of infrastructure equipment is on the order of 10 years, for one thing. Significant performance gains must be proven in the labs before equipment makers invest in network-coding product development. Even then, it is likely that network coding will be added gradually as an overlay to the routing infrastructure on an as-needed basis; a multicast network here, a WiMAX network there. Eventually, network coding may become embedded in routing infrastructure as yet another function.
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