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The appliance, which can be a physical hardware component, software program, or an appliance running in a virtualized environment, speeds up the time it takes for information to flow back and forth across the WAN by using compression and data deduplication techniques to reduce the amount of data that needs to be transmitted. Basically, an accelerator works by caching duplicate files or parts of files so they can be referenced instead of having to be sent across the WAN again.
In the past, accelerators required a dedicated hardware appliance at each end of the WAN link. This arrangement was fine for large enterprise WANs that needed to connect branch offices to a centralized corporate data center, but it didn't help a company's mobile or remote users. WAN accelerator vendors have introduced mobile software clients that act as localized appliances, allowing the remote user's computer to cache duplicate files and parts of files locally. These mobile clients connect either to corporate WAN accelerator hardware appliances or to dedicated headquarters servers. WAN accelerators are often included in wide-area file services (WAFS) vendor products, but they can also function independently.
As the WAN acceleration market has matured, many of the products have evolved beyond the core acceleration techniques. The distinction between WAN optimization controllers (WOC) and traditional WAN accelerators lies in functionality. Like the traditional accelerator appliance, the WOC offers compression and disk caching. However, the WOC further optimizes the WAN link by accounting for known problems with common network protocols. Protocol optimization cleans up chatty protocols used in common enterprise standards such as Common Internet File System (CIFS), Microsoft Exchange, and even TCP/IP, to eliminate the typical overhead found in these communication protocols. These optimizations require a deeper understanding of the protocols and can only be accomplished through significant collaboration with application vendors or reverse engineering by the WAN accelerator vendor.
The third category of application acceleration appliances are known as application delivery controllers (ADC). Unlike WOC solutions, an ADC offering is meant for asymmetrical connections and applications, such as customers accessing a corporate e-commerce site. Without the remote client that WAN accelerators employ, application delivery controllers focus on optimizing the server-side experience using techniques such as Secure Sockets Layer (SSL) offload, static caching, and load balancing to mitigate spikes in the traffic and improve the end user experience.