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Content delivery network architectures

Content delivery network (CDN) technology brings together file access, caching, multimedia delivery and application processing -- while using the advanced policies of the routing and switching infrastructure to ensure survivability and guaranteed delivery.

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Content Delivery Networking (CDN) employs several computers, or nodes, networked across the Internet to deliver large media content to end users and its components.

A technology overlay

A complete network architecture consists of several individual components, or infrastructures, whose purpose is to provide a service to the user community. An example of an infrastructure component could be consolidated file servers, which act as repositories for user files and application data. These servers sit atop another component of the architecture: the routing and switching infrastructure. The foundation for network architecture lies in the routing and switching infrastructure, which provides transport for all other infrastructure components and their various forms of data.

CDNs are considered "overlays" to the routing and switching architecture as well, but they are unique to other infrastructures in that they have the ability to share characteristics of each of them. A CDN can bring together the functionality of file-access, caching, multimedia delivery and application processing -- while using the advanced policies of the routing and switching infrastructure to ensure survivability and guaranteed delivery. A CDN may have the ability to deliver this functionality, but the individual CDN components are key to making it possible.

Elements of a CDN

To deliver features such as file access and caching, a CDN must contain the following elements:

  • Request
  • Distribution
  • Delivery

The "request" element of a CDN deals with the ability of users and systems to ask for specific content, whether it be a file or a video. Because a request occurs at the user end, protocols (such as WCCP) have been developed to intercept and redirect these requests to the hardware components or content engines closest to the user. Once a request has been made, the content engine can decide whether it can answer the request or proxy it on the user's behalf.

The "distribution" element of the CDN determines which decision (answer or proxy) is appropriate. Content has to come from somewhere within the architecture (origin servers), and based on patterns of use and requests, CDN administrators can distribute it appropriately. The choice of distribution, in turn, directly affects the details of a request.

Finally, the "delivery" element is responsible for getting the content to the correct locations within the architecture. This element relies heavily on the routing and switching infrastructure for reliable and efficient delivery.

Hopefully, you now have an idea about CDN technology and the elements that make it an attractive choice for businesses.

About the author:
Doug Downer (CCIE #9848 and JNCIS #881) is a senior consultant with AT&T. Doug has more than eight years of experience in the industry and currently provides high-level business and technology consulting for various federal clients in the Washington, D.C.

This was last published in July 2007

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