Content Delivery Networking: an introduction

Doug Downer gives an overview of Content Delivery Network (CDN) technology and its components, which 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.

In the ever-changing world of technology, there is a growing disparity between the success of companies that can effectively implement newer technology as it becomes available and those that struggle to "keep up with the times."

It appears that before the "bubble-burst" in the late 1990s, little thought was given to the long-term effects that technology could have on business. IT budgets were large, and CIOs were buying into the idea that newer was better -- over and over again.

One legacy of that particular time was the distinct separation among the individual "tech" components within an organization. Within the IT departments, networking and server groups were formed along with application developers and "voice guys." This practice continues in today's environment -- with one key difference: Newer technology is beginning to force these individual groups to unite and work together. Voice over IP (VoIP) brings the "voice guys" and "networking guys" together while such technologies as content switching and SSL VPNs bring the server teams closer to the application developers and security teams.

Content Delivery Networking (CDN) is a concept which essentially has that "bridging" effect within an organization. This week's tip gives an overview of CDN technology -- which 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. Next week, I'll break down some of the individual hardware components and introduce Cisco's integrated CDN products.

About the author:
Doug Downer (CCIE #9848 and JNCIS #881) is a senior consultant with Callisma Inc., a wholly owned subsidiary of SBC Communications. Doug has more than seven years of experience in the industry and currently provides high-level business and technology consulting for various federal clients in the Washington, D.C. area.

This was first published in May 2006

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