Application delivery controllers (ADCs), also known as application switches and application front ends, are a fairly new class of products evolved from server load balancers to address the increasingly complex requirements placed on the network as the data center has continued to grow. ADCs go beyond the network-level load balancing solutions of the past to provide traffic routing, automatic network alerts and a host of other security features -- all while helping to drive down data center management costs. ADCs also assist in improving application response time, so that the move to Web-based applications will not affect user experience. ADCs provide an alternative to the often costly (and rarely helpful) decision to increase network resources to improve application performance.

The new functionality of ADCs is based on how deeply they can effectively look inside a message. Load balancers always had deep packet inspection, and ADCs have taken that a step further -- they can understand the application. ADCs are taking over functions that were formerly performed in the server in order to save server resources, accelerating application response time and providing application-level security, sometimes including an Extensible Markup Language (XML) firewall. All of these features can be provided without any modification to a company's original software design.

Respondents to our Product Leadership survey gave the gold award in ADCs to the Application Control Engine (ACE) family from Cisco. Available as an appliance, gateway or a module for Catalyst 6500 Series switches or 7600 routers, ACE employs Layer 7 content switching integrated with patented acceleration technologies and data compression. Server performance is improved by offloading and caching Secure Sockets Layer (SSL), TCP and XML.

More than 70% of Cisco ACE family users surveyed said they saw good or excellent server and appliance load balancing with the product line. Just over 75% of survey respondents rated their server offloading good or excellent, and more than 70% lauded the product family's security and application acceleration. One respondent praised the product by saying that the only words to describe it were "absolutely excellent."

Jessica L. Dempsey, Assistant Editor