Content Delivery Networks

Fabrikam is essentially building a Content Delivery Network (CDN) for an enterprise. (This type of network is sometimes called an eCDN.) The CDN concept has become popular as a way of describing a decentralized system for delivering content over the Internet.

Service providers such as Akamai and Network Appliance offer services, applications, and hardware to help companies host their content on the Internet. Some providers manufacture the hardware or software in addition to offering a hosting service—a complete CDN solution. The solution can include an array of edge servers located throughout the world, or content management systems that move the content to the edge servers and provide usage feedback. An Internet radio station, for example, can simply send its encoded signal to a CDN, which can then handle all the distribution. Users simply access the URL of a streaming site, and CDN software automatically redirects the client to the edge server that will provide the best playback quality. For more information about CDNs, see chapter 13.

Following the success of CDNs on the Internet, several companies packaged their services and devices for use on private intranets run by medium-to-large enterprises. With these devices and the associated software, you can create an eCDN that delivers Windows Media-based streaming content—as well as Web content and other multimedia content—on an intranet. Many of the appliances are standalone devices that you simply install, configure once, and then manage remotely.

An eCDN system helps companies manage content and bandwidth by providing components for storage, content distribution, intelligent delivery, and reporting, as shown in figure 20.7. Most eCDN solutions are flexible and scalable. You can put together the components to deliver streaming media content over just about any type and size of IP network. The infrastructure of an enterprise network often presents the most challenges for upgrading an intranet for streaming. Edge servers and an eCDN system for managing content can help you work around the challenges.

Figure 20.7: Components of an eCDN system.

An eCDN system enables both push and pull approaches to content management. IT personnel can push or prestuff content to the remote sites that they feel will receive a high number of hits. Users can also pull content from the origin server if the content is not available in the remote cache.

An eCDN system consists of the following components:

• Storage. A file server or storage device that can hold large amounts of data, and then access it quickly and reliably over sustained periods. It must also be capable of streaming the data to a number of clients concurrently. Storage solutions include:

  • Direct Attached Storage (DAS), such as hard drives attached directly to a server.

  • Network Attached Storage (NAS), which are servers that only provide file storage.

  • Storage Area Network (SAN), which provide high-speed, private networks of shared storage devices.

  • Redundant Array of Independent Disks (RAID), which are arrays of hard drives that can provide various levels of storage-access speed and fault tolerance.

• Content Distribution. Computers, appliances, and software that manage content distribution from origin servers to edge servers.

• Intelligent Delivery. Many CDNs use software that enables “intelligent delivery” of content. For example, if an end user in New York uses the Internet to request a video stream from an origin server in Oslo, the CDN software automatically locates the content on the edge server that will provide the best connection and stream quality. It can also provide a type of load-balancing function so that the closest server with the lowest number of concurrent users and the most available bandwidth is used.

• Reporting. A single Windows Media server creates daily usage logs, providing a detailed view of client activity. In an eCDN system, many servers are used, with each creating its own usage logs. An important component of a complete eCDN system is automatic collection and compilation of usage logs, as well as tools for creating reports from the data. The usage logs and reports can provide important performance and usage information. IT staff can ascertain the health of the system and pinpoint trouble spots, and content producers can learn how to improve their programming to better meet the needs of viewers.

Edge serving and content-management solutions provide exciting areas of growth for the streaming media industry. Instead of an independent, centralized point of origin for content that relies heavily on a solid, immoveable infrastructure, the eCDN approach views the network as one dynamic organism that can change and grow.