Content Delivery Networks (CDN) are based on systems of multiple data centers. Such centers are distributed all over the globe to locate data geographically closer to the end user. Every time new request appears in a concrete geographic place, CDN temporary copies requested data to the closestCDN server. If this request will be regular, then data will be stored. Users will get requested data from the closest CDN server, that has such content. Actually, proximity is not the only reason, that CDN takes into account to choose CDN server for request. The number of available ports on the concrete CDN server is also has a big influence on a decision. There are some other reasons, that can be included in a CDN algorithm of taking decisions for users requests. After all, network distribution system is a complex multi-level mechanism, which must rapidly respond to the changes in the environment.
Different CDNs are based on a different number of PoPs (Point of Presence). For online business, which is going to select a CDN company, this number can be very important. As well as how these PoPs are distributed all over the globe. Concrete online business should correlate these numbers with its statistic. This can be the statistic of past requests – their geographical spread, amount and periodicity. The most popular CDN companies have the following number of PoPs:
- Amazon CloudFront – 52 PoPs all over the globe – 20 in North America, 16 in Europe, 14 in Asia Pacific and 2 on other continents;
- CDNsun – more than 85 PoPs- 25 in America, 44 in Europeand 16 in Asia Pacific;
- CDN77 – 27 PoPs – 7 in North America, 11 in Europe, 6 in Asia Pacific and 3 on other continents;
- CacheFly – 41 POPs – 12 in North America, 16 in Europe, 8 in Asia Pacific and 5 on other continents;
- MaxCDN – 16 POPs – 9 of them are in North America, 3 in Europe and 4 in Asia Pacific.
Network CDN is growing with the growing Net and demands. If demand grows, CDN companies can allow to build or rentmore data centers. Usually data centers are placed closer to a PoPs. This influences on an uptime. Data center consist of information infrastructure, telecommunications infrastructure and engineering infrastructure. Information infrastructure includes server hardware and provides the basic functions of the data center – data processing and storage. Telecommunications infrastructure provides data transfers between the data center and users, as well as interconnection of elements of the data center. Engineering infrastructure ensure the proper functioning of the main systems. Due to size, data centers can be divided in five groups – Large data centers, Modular data centers, Average data centers, Small data centers and Containerized data centers. Large data centers have their own specially designed buildings with own connects to the server and communication channels. Modular data centers can be designed very differently, they are assembled from modular units. Containerized data centers are quite useful because they are designed to be transported by rail or road.