Content delivery networks or content distribution networks are hardly new systems. They have been a growing part of the Internet since the nineties. Nowadays they become an integral part of the Internet’s content food chain. Nearly 100 percent users all over the globe deal with different CDNs day by day (especially with the video distribution network). Such systems consist of multiple servers distributed in different countries. Content delivery is based on a principle of technological closeness to the end user. Usually technological closeness matches geographical, but not always. Server can be close to users due to combined characteristics: geographical closeness, available ports on way to user and also maximal capacity of cables on a way. Every time when delivery system processes the request it decides which server or servers are the closest due to above mentioned characteristics.
The idea of content distribution is to satisfy every user request by giving needed content from technologically close servers, not from the edge server. This gives better responsibility, faster page load time and other processes, which make users (and online-business) more satisfied (for example faster video content delivery). Normally, delivery systems use caching to prevent server’s overload. Caching involves storage of only popular content. Generally, it works in three steps. Initially request for a new specific content goes to the edge server (because there is no such content in CDN servers). After that content distribution system copies requested content to servers, which are close to the place of the request creation. Finally, if content becomes popular, storage continues, if not – server deletes the information.
Video content delivery network become very popular distribution system nowadays. At first, video delivery was complicated, when it was carried out only by general purpose CDNs. Thereat users had only one way to get video content – to download the entire file before watching. Needless to say, that such way of video delivery is not so popular – it takes a long time to load a large video file. Video content distribution network has been developed with the advent of on-demand video technology. Actually, it is close to the previous technology, but useful for users. Like general purpose delivery systems, on-demand video uses direct download of the video file, but it can start to show video within 2-3 first seconds. File download continues in the time while user is watching the video. Video on-demand was strongly popularized by such services as YouTube since 2006 year and still very useful. Video delivery network always tries to avoid technologies, which require streaming servers. Every streaming server is very expensive. Furthermore, technology with streaming servers involves very high-bandwidth pipes between a central location and the end-user. This is much more expensive than streaming servers. However, live video streaming cannot work like video on-demand, because it doesn’t have finally generated file. That is why such big events as Olympic Games, FIFA World Cup and others can cover only few large streaming companies in the world.