Introduction to CDN

Solution

The solution to all the problems above is Content Delivery Network (CDN). A CDN is a group of geographically distributed proxy servers. A proxy server is an intermediate server between a client and the origin server. The proxy servers are placed on the network edgeThe network edge is the zone where a device or local network interfaces with the Internet.. As the network edge is close to the end-users, the placement of proxy servers helps quickly deliver the content to the end-users by reducing latency and saving bandwidth. CDN has added intelligence on top of being a simple proxy server as we will realize in the next lesson.

We can bring data near the user by placing a small data center near the user and storing copies of the data there. CDN mainly stores two types of data: staticThis type of data does not change frequently and remains on the servers for a long period. and dynamicThis type of data changes most frequently e.g. newsletters, ads, live video, etc.. CDN primarily targets propagation delay by bringing the data closer to its users. CDN providers go the extra mile to have sufficient bandwidth available through the path and bring data closer to the users (possibly within their ISP). They also try to reduce transmission and queueing delays because presumably, ISP will have more bandwidth available within the autonomous system.

Let’s look at the different ways CDN is solving the problems above:

1. Latency: CDN brings the content closer to end-users thus reducing the physical distance and consequently the latency.
2. Data-intensive applications: Since the path to the data includes only the ISP and the nearby CDN components, there is no issue in serving a large number of users through a few CDN components in a specific area. As shown below, the origin data center will have to provide the data to local CDN components only once whereas local CDN components can provide data to different users individually. No user will have to download their own copy of data from the origin servers.

Various streaming protocols are used to deliver dynamic content by the CDN providers. For example, cdnsun uses the RTMP (Real-Time Messaging Protocol), HLS (HTTP live streaming), RTSP (Real-Time Streaming Protocol), etc., to deliver dynamic content.

3. Data center resources: CDN is used to serve popular content. Due to this reason, most of the traffic is handled at the CDN instead of the origin servers. Thus, the load on origin servers is shared by different local/distributed CDN components.