WAN Accelerators

We tested three units per vendor (a central office unit and two remote units). Generally, you'd need one more WAN accelerator than you have WAN links: one central office unit, plus a unit in each branch office. And because each manufacturer uses proprietary compression, all the devices must be from a single vendor.

The accelerators can be deployed in a hub-and-spoke or mesh topology, based on your organization's setup. Devices that require you to create links manually, however, are difficult to configure in a mesh environment. That's one limitation of Expand's and Swan Labs' accelerators. By comparison, Packeteer's PacketShaper Xpress, which detects peers and sets up a compression tunnel automatically, makes the configuration process easier across the board.

You'll also want to consider using each vendor's centralized management software, especially if you're managing a large number of WAN links in a mesh setup. Centralized management software can be deployed anywhere, but ideally on a separate Windows server in the central office. The management software polls all units and pushes configuration files to all appliances.

Rules of Compression

As a general rule, the more compressible the data--text files and Web pages, for instance--the better the throughput. In one of our benchmarks, we transferred 30 Web pages over a simulated T1 link in 93 seconds. With compression enabled, that time fell dramatically: 24 seconds, for example, when we tested Peribit's SM-500. Binary files, nonrepeating data, VoIP (voice over IP) traffic, streaming video and already compressed traffic don't fare as well as Web and text files. When we transferred a 15-MB data file composed of random ASCII and extended ASCII characters, we shaved off only a second or two.