Campus Network Design Fundamentals

The following services fall under the CN umbrella:

• Efficient distribution of content across the network

• Selection of the best site for a user to obtain the content

• Load balancing of content stored on multiple devices

The components of a CDN can include the following:

• Content cache or content engine A content engine is a device that caches, or stores, selected content from origin servers (servers from which the content originates) and sends it upon request to users. Content engines can be located, for example, at each branch office to reduce the WAN bandwidth required by the branch-office users.

• Content router Content routers direct users' requests for content to the closest content engine.

• Content distribution and management device This is a device, such as the Cisco Content Distribution Manager, that is responsible for distributing content to the content engines and ensuring that the material is kept up to date.

• Content switch Content switches load-balance requests to servers or content engines. For example, a content switch can be deployed in front of a group of web servers; when a user requests data from the server, the content switch can forward the request to the least-loaded server.

A CDN does not have to include all of these components. For example, content engines can be deployed as stand-alone devices. Alternatively, a Cisco Content Distribution Manager can be deployed to manage the content engines, and content routers can be added to redirect content requests. Content switches can also be deployed with or without any of the other components.

Because CN is considered a network solution, it requires a robust network infrastructure and appropriate network services to be in place. The network services required by CN include quality of service (QoS), security, and IP multicast.

Note

IP multicast reduces the bandwidth used on a network by delivering a single stream of traffic to multiple recipients (defined in a multicast group), rather than sending the same traffic to each recipient individually. IP multicast is explained further in Chapter 10, "Other Enabling Technologies."

The CDN components are further described in the following sections.