Content Delivery Network – Primer

Content Delivery Network or Content Distribution Network is a group of network servers located in the data centers around the world aiding in the faster retrieval of  contents to the internet users.  These distributed servers cache the static information for a content providers. CDN’s help to retrieve the static contents upon user request from a geographically closer CDN server using an algorithm, thus enabling a quicker response for the users request. Without CDN, these requests would be delayed especially if the client and the content provider are far apart. The dynamic content would still be available in the content providers network. The static contents that are being provided have some sort of versioning in the contents. If the appropriate version of the static content is not present in the CDN servers, then a cache miss occurs. Whenever there is a cache miss, the CDN servers request for the static data from the content provider server and cache the data in their local servers. By this way. any request for accessing the static content can be full-filled by the CDN servers.

CDN’s either use their own data centers or use the data centers from ISP. The content providers pay the CDN provider for ensuring the reliability and efficient access to the contents. The CDN providers inturn pay to the ISP for hosting the servers in the data centers if they use the ISP data centers.  These geographically located CDN servers are called surrogate servers.

Akamai is one of the most popular and early entrant in the CDN world.  In the CDN world, the servers being managed by the CDN are called surrogate servers. These surrogate servers are interconnected to each other. They also form a hierarchical patters – parent <-> child surrogate servers. These surrogate servers in the network are typically connected by  a “CDN pairing gateway” which interconnects two or more CDN which are separately administered.

These CDN’s also interact with the accounting system of the content provider so that the contents are provided to the users based on the subscription validity of the clients.

The core and access routers in the network are powered to pull the data from the appropriate surrogate servers (or these routers act as surrogate CDN servers caching the information?) thereby enhance the speed of retrieval of data.  The standards for the CDN network are not clearly defined as of now and would certainly empowered the next generation of the internet boom (esp for video services).


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