First, let us look at the basic structure and data transmission of the traditional Internet network.
According to the traditional network structure, the user's access process is basically as follows:
1. The user enters the domain name of the website to be visited in his browser;
2. The browser requests the local DNS to resolve the domain name;
3. The local DNS sends the request to the DNS server authorized by the website ;
4. Authorized DNS sends the server's IP address as the resolution result to the local DNS;
5. The local DNS returns the analysis result to the user and saves the analysis result in its own cache until the corresponding TTL (lifetime) expires before requesting analysis from the authorized DNS of the website;
6. After obtaining the IP address, the user visits the server of the website pointed to by the address;
CDN = smarter mirroring + caching + traffic diversion. CDN can not only cache video content, it can also distribute static resources of the website (such as various types of pictures, html, css, js, etc.), and distribute static content of mobile applications (such as installation package apk files, Pictures, videos, etc.) for distribution.
If a user wants to access the video-on-demand content of a video website, the specific cdn acceleration principle steps are:
① When the user clicks on the content on the APP, the APP will go to the local dns (resolution system) according to the URL address to seek IP address resolution.
② The local DNS system will transfer the resolution power of the domain name to the CDN dedicated DNS server.
③ The CDN dedicated DNS server returns the CDN's global device IP address to the user.
④ The user initiates a content URL access request to the load balancing device of the CDN.
⑤ The CDN load balancing device selects a cache server in the area to which the user belongs based on the user's IP address and the content URL requested by the user.
⑥. The load balancing device tells the user the IP address of this cache server, and allows the user to initiate a request to the selected cache server.
⑦. The user initiates a request to the cache server, and the cache server responds to the user request and transmits the content required by the user to the user terminal.
⑧. If there is no content that the user wants on this cache server, then this cache server will request the content from the source server of the website.
⑨, the origin server returns the content to the cache server, the cache server sends it to the user, and according to the user-defined caching strategy, it is judged whether or not to cache the content on the cache server.
In short, CDN uses more cache servers (CDN edge nodes), which are deployed in areas or networks where user visits are relatively concentrated. When a user visits a website, the global load technology is used to direct the user's visit to the nearest cache server, and the cache server responds to the user's request.