A new generation of WAN accelerator products, designed specifically for Microsoft Windows environments, has recently become available. They facilitate sharing MS Office documents among users at remote offices by greatly reducing the amount of time required to access Office files such as Word, Excel and PowerPoint. These products reduce the time required to open, read and save large files across a WAN from minutes to tens of seconds. In addition to cutting WAN costs, they can eliminate the need to maintain fileservers at remote locations.
Windows-specific WAN accelerators use techniques specific to Windows in addition to compression and smoothing to accomplish these performance improvements. The techniques used are:
- Network round trip reduction
- File read ahead and local caching
- Elimination of unnecessary file operations
The CIFS file access protocol used by Windows was designed for LANs and requires a large number of sequential messages and responses between the fileserver and client to accomplish each file operation. An accelerator is placed at the datacenter and at each remote site. These accelerators recognize the protocol sequences for common operations: They reduce the
MS Office products read files page by page, accessing only the part of a file requested by the user. WAN accelerators anticipate that when the user opens a file and reads the first page, the rest of the file will eventually be requested. The data center accelerator reads the entire file and sends it to the remote where it is stored on the remote accelerator's disk, ready to respond to a request from the user. Accelerators cache recently accessed files to eliminate redundant copies in transfers when the same file is used by multiple users at a remote site. Also, some of the these products can be configured to pre-load designated files in advance of any request.
Office products require an entire file to be rewritten if even a small part of the file has changed. WAN accelerators of this type recognize which parts of a file have been changed and rewrite only those parts. In addition, when an older copy is cached at a remote site but changes have been made to the version at the data center, the remote accelerator requests the modified part of the file and merges it with the cached version in anticipation of a future request for the file.
Optimizing access to Office files is the primary benefit of these accelerators, but some also include optimizations for other applications such as e-mail. When an e-mail is sent to more than one user at a remote site, the accelerators recognize this and transfer the message across the WAN only once. In addition, some of these accelerators optimize web access and Oracle and Sybase database operations.
Some WAN accelerator products include such features as: a choice of compression algorithms so you can tune the accelerator for the best performance on your data, QOS features so you can prioritize data and UDP compression. Test products on your network before you make a purchase to make sure that the selected product matches your network traffic mix.
David B. Jacobs has more than twenty years of networking industry experience. He has managed leading-edge software development projects and consulted to Fortune 500 companies as well as software start-ups.
This was first published in August 2005