Web front-end accelerators use a grab bag of techniques to speed delivery of content, including application-layer switching, HTTP compression and TCP multiplexing.

The problem is that Web front-end devices either make traffic go very fast for a limited number of users or handle a very large number of users - but they can run into trouble doing both at the same time.

That's the major conclusion of the industry's first comprehensive performance tests of Web front-end devices. For nearly a year, we benchmarked devices from leading vendors Array, Citrix, Crescendo Networks, F5 Networks, Foundry Networks and Juniper Networks.

Among our findings in this inaugural test:

• The benefits of application acceleration are real. Properly implemented, devices can speed delivery of content to users while simultaneously lightening the load for data-center servers.
• HTTP compression doesn't always reduce response time, and can increase it in some situations, even with highly compressible text objects and very low client access rates.
• TCP multiplexing can dramatically reduce network processing overhead on servers, by nearly 350-to-1 in one case.
• Some devices don't offload much TCP connection processing when users request pages quickly (as on e-commerce sites).
• Web front-end devices exhibit big variations in the maximum number of connections they handle and the maximum rates at which they move traffic.

As is often the case with any new market category, there are substantial differences in terms of form factor, topological requirements and supported features (see "One size doesn't fit all").

Because of those differences, and because this is a relatively new product category and no device aced all tests, we're not scoring products this time around. As our results clearly show, different Web front-end vendors have put their development dollars in different places.