Vendors choose to tout disparate application-acceleration techniques

Feature-by-feature breakdown of Web front-end devices.

In the emerging market for application-acceleration devices, there's inevitably going to be confusion about what constitutes a base feature set.

To help establish apples-to-apples features comparisons among products in our inaugural performance test (see test results), we circulated a survey to participating vendors (Array, Crescendo, Citrix, F5, Foundry and Juniper) asking them to pinpoint what each offered in terms of Layer-7 switching, URL inspection and rewriting, HTTP compression, caching, TCP offload and surge protection.

While most vendors already offer all these features, or have plans to do so in the near future, the priority they place on each varies widely. (See vendor priority chart). As we advised in our performance test, it's wise to understand what kind of performance boost you expect from these devices, and go with the vendor that's made the biggest investment in that particular area.

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In the emerging market for application-acceleration devices, there's inevitably going to be confusion about what constitutes a base feature set.

To help establish apples-to-apples features comparisons among products in our inaugural performance test (see test results), we circulated a survey to participating vendors (Array, Crescendo, Citrix, F5, Foundry and Juniper) asking them to pinpoint what each offered in terms of Layer-7 switching, URL inspection and rewriting, HTTP compression, caching, TCP offload and surge protection.

While most vendors already offer all these features, or have plans to do so in the near future, the priority they place on each varies widely. (See vendor priority chart). As we advised in our performance test, it's wise to understand what kind of performance boost you expect from these devices, and go with the vendor that's made the biggest investment in that particular area.

A complete summary of the survey results follows.

Layer-7 switching means a device uses application-layer criteria to determine where to send a request. This gives Web front-end devices more granular control over forwarding decisions than is possible with conventional Layer-4 load balancers. For example, if a given HTTP URL ends in ".html," the request might be passed to a group of servers handling text content, while a URL ending in ".jpg" might instead go to a group of image servers. Layer-4 load balancers, in contrast, see only Web requests destined to TCP Port 80, so no further differentiation among server groups is possible.

F5 ranks Layer-7 switching as the top feature contributing to the success of its device at serving of Web content faster. Central to all content switching in F5's BIG-IP Local Traffic Manager is its purpose-built network operating system - Traffic Management Operating System - and iRules, the vendor's policy engine. This combination isolates clients from server-side flows with a proxy service, then inspects the packets to understand sessions in terms of application, browser, content and connection mode, and finally switches the packets based on rules defined in the iRules schema.

Foundry, Crescendo and Citrix all place Layer-7 switching at the top of the list of features, as well.

As part of the ServerIron's HTTP Content Switching feature, the Foundry device can inspect both header and payload of all HTTP traffic. The ServerIron uses this information to filter, switch, redirect and load-balance packets and connections across back-end servers. A similar feature called Total Content Analysis provides the same capabilities for non-HTTP applications, including those based on DNS, Session Initiation Protocol, Financial Information Exchange protocol, Windows Terminal Services and RADIUS.