More ABCs of ADCs

Insightful analysis by consultants Steve Taylor and Jim Metzler, plus links to the latest WAN news headlines

In our last newsletter we began the discussion of the types of functionality provided by an Application Delivery Controller (ADC). We will continue that discussion in this newsletter by outlining some additional functionality provided by ADCs.

The role of ADCs

Secure Socket Layer (SSL) is widely used to encrypt documents that are being sent over the Internet. Unfortunately the processing of the security mechanisms that are associated with SSL is computationally-intensive. As a result, a key function of an ADC is SSL offload. As part of SSL offload, the ADC terminates the SSL session and performs the computationally-intensive processing of the security mechanisms thus freeing up server resources.

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In our last newsletter we began the discussion of the types of functionality provided by an Application Delivery Controller (ADC). We will continue that discussion in this newsletter by outlining some additional functionality provided by ADCs.

The role of ADCs

Secure Socket Layer (SSL) is widely used to encrypt documents that are being sent over the Internet. Unfortunately the processing of the security mechanisms that are associated with SSL is computationally-intensive. As a result, a key function of an ADC is SSL offload. As part of SSL offload, the ADC terminates the SSL session and performs the computationally-intensive processing of the security mechanisms thus freeing up server resources.

One of the characteristics of most IT environments is that the environment is comprised of a large and growing number of servers and applications. Another characteristic is that most IT organizations have very limited control as to which users access which applications and which servers. An ADC gives control to the IT organization through functionality sometimes referred to as scripting, and sometimes referred to as a rules engine. This functionality allows the IT organization to directly classify and modify the traffic of any IP-based application.

The basic role of compression is to reduce the amount of traffic that has to be transmitted over the WAN. One of the factors that impacts how effective the compression provided by an ADC will be is the type of traffic. For example, applications that transfer highly redundant data, such as text and html on Web pages, will benefit significantly from compression. How the compression is implemented within an ADC also impacts its effectiveness. For example, compression that is performed in hardware in the ADC is likely to be more effective than compression that is implemented in software.

If an ADC supports caching, new user requests for static or dynamic Web objects can often be delivered from a cache inside of the ADC rather than having to be regenerated by the servers. Caching therefore improves user response time and minimizes the loading on Web servers, application servers and database servers.

Our next newsletter will quantify the difference between the value of a server load balancer and the value of an ADC.

Read more about lans & wans in Network World's LANs & WANs section.

Steve Taylor is president of Distributed Networking Associates and publisher/editor-in-chief of Webtorials. Jim Metzler is vice president of Ashton, Metzler & Associates.