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Content Delivery Networks

Chapter Description

Content Delivery Networks (CDNs) enhance the end user's experience by overcoming some inherent flaws in the Internet's anatomy and provide a solution to what was once a major challenge. This chapter covers how CDNs increase overall network performance by solving existing challenges, presents the components of a CDN solution, and provides recipe-based solutions that help in deploying a CDN architecture.

Applications of Content Delivery Networking

Transparent Caching

To fully realize the value of caches, enterprises and service providers can implement transparent caching. In transparent caching, the cache intercepts the connection to an origin World Wide Web server, handling all HTTP traffic without requiring explicit browser configuration, easing IT pressures at enterprises and service providers by eliminating the need to preconfigure user browsers. It also removes the problem of users covertly changing their browser settings to bypass the cache because traffic is sent through the cache transparently.

Cisco improved transparent caching by developing Web Cach Communication Protocol (WCCP) and high-performance caches to take full advantage of this Cisco IOS Software-based protocol. WCCP is the open, defacto standard protocol from Cisco that enables a router to redirect content requests to a cache, fully leveraging cache performance and performing basic load balancing across multiple caches in a cluster. Cisco Content Engines are network devices optimized to accelerate content delivery by locally storing frequently accessed content (such as GIFs, JPGs, and MPEGs) and quickly responding to user requests instead of going to the origin server. The combination of Cisco WCCP-Enabled Routers and Content Engines provides a powerful Network Caching Services Solution for accelerating content delivery and reducing WAN bandwidth costs for enterprises and service providers. Figure 5-7 and the associated list that follows illustrate the solution.

Figure 5-7Figure 5-7 Mechanics of Transparent Caching

  1. A user requests a World Wide Web page from a browser.

  2. The Cisco WCCP-Enabled Router analyzes the request and, based on TCP port number, determines if it should transparently redirect the request to a Cisco Content Engine. Access lists can be applied to control which requests are redirected.

  3. If a Cisco Content Engine does not have the requested content, it does one of the following things:

    1. It sets up a separate TCP connection to the end server to retrieve the content.

    2. The content returns to, and is stored on, the Cisco Content Engine.

  4. The Cisco Content Engine sends the content to the end user. From its local storage, the Cisco Content Engine transparently fulfills subsequent requests for the same content.


Cisco System's Enterprise Content Delivery Network (E-CDN) solution enables high-quality, high-bandwidth streaming video, rich audio, large graphics, presentations, and documents to be delivered over corporate wide-area and local-area networks in an efficient manner. It utilizes the Self Organizing Distributed Architecture (SODA) protocol, which takes advantage of existing bandwidth to efficiently route high-bandwidth content over enterprise networks or even over the Internet. This process eliminates network bottlenecks that often accompany the distribution and retrieval of large multimedia and streaming files.

Cisco E-CDN components include a Cisco CDM for centralized media distribution, a Content Router for redirecting client requests to the closest media source, and Cisco content engines (CEs) which poll the Cisco CDM for new content and ultimately fulfill the client browser requests.

Implementing rich media distribution and retrieval in an enterprise environment can enable opportunities across the organization. These opportunities include delivery of rich media (audio/video, large files of any type) across last mile constraints for remote offices. Businesses can use this technology to quickly and cost-effectively distribute e-learning programs, corporate and field communications, software downloads, and so on from one centralized location (corporate HQ) to any number of remote offices or storefronts. This all leads to improved productivity, competitiveness, and a decreased time to market. The E-CDN architecture enhances an enterprise network's scalability, reliability, and built-in redundancy by supporting a rich knowledge exchange environment where employees, partners, and customers can contribute and learn from each other.

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