| By :
Dirik Hameed
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. The companies that offer this service are usually independent and make use of existing internet infrastructure. More recently broadband service providers have introduced their own CDN solutions to improve their service. Some providers also make use of peer-to-peer networks that do not require central servers or stable hosts. A CDN is comprised of a network backbone that connects many different nodes or edge servers, redundant central servers and fallback servers. There could be thousands of different nodes and these are distributed so that they are as physically close to the end user as possible. Content is then duplicated on to many different edge servers so that it can be accessed from many different points. 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. When you need to deliver content that requires high bandwidth capability this is the ideal solution and it is used by online broadcasting and video download services. One of the big advantages is scalability. If there is very high demand the content can be accessed from multiple nodes and so the system won't crash. 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to the website of the host server then you will end up with many copies that are cached on the network that would be out of date.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.
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