The purpose of a content delivery system or CDN is to distribute content to multiple nodes so that it becomes more easily accessible. Rather than distributing content from central location where it would always travel across large parts of the network it is stored at nodes that are closer to the peripheries. It can then be accessed from the closest point or in the case of spikes in demand it can be accessed from multiple locations.

CDN networks operate as an application service provider (ASP). The infrastructure that is used can then be outsourced and can be changed as needed. Some internet service providers make use of their own systems for content delivery. This gives then the advantage that they do not have to pay a secondary provider for the infrastructure. Some networks also use peer-to-peer systems that do not require centralized servers.

There will always be a backbone networks that connects all the nodes which might consist of thousands of edge servers. Except in the case of peer-to-peer there will also be central servers where backup information is stored. Content is stored on the central servers which are closest to the nodes that are used most often. From here it will be sent to many different nodes where it can be accessed as needed.

When there is a request for content the system will direct that request to the node which is most suitable. This would be either because it is the closest or because it is the closest server which is not at high capacity. You therefore get the fastest possible connection using the least amount of network resources. In some cases the data can also be routed to take advantage of the least expensive links.

A CDN is ideal for mass content delivery for this reason. If there is great demand over a short period such as during the viewing of a popular program then there is instant scalability. If this content was to be distributed from a central server there would be severe limits on it rate of transfer but if it is distributed to thousands of different nodes then this problem can easily be overcome.

The effective broadband capacity is also increased with every added node. If the backbone network has a capacity of 10Gbit/s then that would be the limit for transfer across the system. If each separate node could be accessed at 10Gbit/s then that could be multiplied for every node that is available. Say there where 100 nodes with the same content on then it would be possible to transfer at 1Tbit/s.

Any kind of content can be distributed by a CDN and this includes static or dynamic websites. If there are any changes to the website of the host server then you will end up with many copies that are cached on the network that would be out of date. By using ESI (edge side includes) these can now be instantly updated when changes occur.

Along with scalability CDN has another advantage in common with cloud networks and that is redundancy. Because there are so many different copies of the same information in many different locations it will always be backed up. There will also be a high level of availability because if any part of the network is down the same request could be sent to another part of it.