A content delivery system or content delivery network (CDN) makes it possible for large amounts of data to be transferred more efficiently. To do this it distributes copies of the content across the network so that it can be accessed from multiple points. Requests for this information can then be routed to the nearest point or the one that has the least traffic.
CDN hosting is supplied by an application service provider (ASP) and can make use of existing infrastructure that is paid for as it is used. Telcom providers have also been introducing content delivery networks on their own infrastructure. There are also some providers that rely on peer-to-peer networks
For a CDN to operate it does require a backbone network. This will connect all of the servers and is optimized for packet data delivery. When there are multiple servers the content will be stored in the one which is closest to nodes from which it is accessed most often. Edge servers are obviously limited in size and cannot carry a copy of all of the data that it has access to. Information will therefore be moved back and forth according to demand and where that demand is coming from.
The application software will route request for content to the server which is closest or which has higher availability. This means that less of the overall network is used which reduces the overall load on it. Downloads will be quicker and more stable but there will also be a lower costs if the network is paid for as it is used. The software also decides how the information is moved around as demands change.
The ideal usage is for high volume content that requires a lot of bandwidth like music and video downloads or online broadcasting but any kind of website can make use of a CDN. When there is a big demand for certain content it can be accessed from many different locations which increases reliability and quality of service. The effective bandwidth of the entire system is also increased.
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.
CDN is not just for digital content and it does provide better access to both static and dynamic websites. The problem with having copies of these all over the internet is that they all have to be update when the website on the host server is updated. This problem is overcome using edge side includes or ESI.
It is not just scalability that CDN has in common with cloud servers. Because of all the different copies of data that are on the network there is a high level of redundancy. This means that if any part of the system goes down the content will still be available on other parts of it. You also might not need online backup services with so many copies on the net.