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Look Out for Layer 5

For many businesses, wide area networks (WANs) can sometimes seem more like a back road than part of the information superhighway. Network congestion, protocol latency, and even sheer physical distance all work together to slow down and drop packets as they cross the WAN. Application performance suffers exponentially to WAN latency and packet drops. For instance, 1 percent packet loss can result in more than an 80 percent reduction in application performance.

There's a thriving market for products trying to solve these problems, and several competing technologies are handling it by accelerating traffic across the WAN. To extend the highway analogy, imagine you have two ways to speed traffic up. One technology lets you increase speed limits, so all traffic on the highway moves more quickly. Another lets you create a "diamond" lane reserved for the fast cars, while all other traffic uses the slower lanes.

Technologies working at Layer 3 of the OSI model, the packet-processing layer, accelerate all traffic over the WAN by reducing the duplication of data in the data stream as it enters the WAN. These technologies have two key shortcomings: First, they require significant processing resources and in some cases can actually slow down traffic. Second, Layer 3 technologies are not aware of the functions of the applications merged into the data stream, so they are unable to speed up traffic for any specific application.

Other technologies accelerate the performance of individual applications by compressing data at the application layer, Layer 7. However, because it is mixed in with WAN traffic that is not compressed, it is impossible to guarantee that the compressed application will consistently perform as required.

A new technology is emerging, one that combines WAN optimization and application acceleration to radically improve performance over the WAN. By operating at the session level, Layer 5, it is able to examine application data streams before they merge, so it finds and removes more redundancies than Layers 2-3 methods. And because it looks at all application data streams, this new technology compresses more types of traffic than Layer 7 technologies.

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