The proliferation of apps assuming LAN speeds has put pressure on WAN sites that don’t enjoy unlimited bandwidth.
Data compression is a key technology for reducing such stress. It works well for most data, except for real-time multimedia – such as Voice over IP (VoIP) or video conferencing — which are already compressed and can’t benefit from simple compression techniques.
WAN optimization products implement compression in many ways, including:
This method takes streams of data and sends a reduced version of the content across the circuit, saving bandwidth. Standard compression in a WAN environment has many subtleties, including the choice of algorithm, how compression works across streams, and the interaction between compression and encrypted traffic.
This technique reduces data by maintaining a stored version of recently requested data objects (typically, files or email attachments) at the remote side of the connection. If a data object is requested a second (or third, or fourth) time and it is in the cache, then that copy is returned, eliminating the need to re-transmit the object from the central site to the remote site.
Caching is especially useful in environments where file sharing is done across the WAN (using programs such as SharePoint, protocols such as Server Message Block), or where the email server (typically Exchange) is located at the central site and not the remote site.
This approach reduces data by detecting duplication in streams of bytes. Deduplication is a term from the world of storage and backup systems — think of all those nearly identical copies of the C:\WINDOWS\DIRECTORY in a typical backup server and it’s easy to understand the benefit of deduplication.
The actual details pertaining to which of these algorithms is used and whether the vendor calls it caching or deduplication is mostly irrelevant. One important difference is that caching nearly always requires a hard disk of some sort to hold cached data, while deduplication is handled on the fly without any persistent storage.
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