What is CDN? Understand the Working Principles of CDN in 5 Minutes!

​CDN (Content Delivery Network)

A Content Delivery Network (CDN) is a distributed network of servers strategically placed in multiple data centers around the world. The primary purpose of a CDN is to deliver content—such as web pages, videos, images, and other media—to users more efficiently based on their geographical location.

1. Caching: When a user makes a request for content from a website, the CDN caches (stores) a copy of that content on one of its servers located closest to the user’s geographic location. This server, called an edge server, acts as a cache. Subsequent requests for the same content can be fulfilled by the edge server, reducing the load on the origin server where the content is originally stored.

2. Reduced Latency: By storing content closer to the end-users geographically, CDNs reduce the physical distance that data needs to travel. This proximity decreases latency, resulting in faster loading times for websites and content delivery.

3. Load Distribution: CDNs distribute incoming traffic across multiple servers, balancing the load and preventing any single server from being overwhelmed. This helps in improving website performance and reliability, especially during peak traffic periods or sudden spikes in visits.

4. Security: CDNs often provide security features like DDoS protection, Web Application Firewalls (WAF), and secure socket layers (SSL) certificates to mitigate cyber threats. By filtering out malicious traffic and securing data transfer, CDNs enhance the overall security posture of websites.

5. Scalability: CDNs offer scalability by allowing websites to handle increased traffic without requiring significant infrastructure upgrades. As traffic grows, CDN providers can automatically scale up resources to accommodate demand, ensuring consistent performance levels.

6. Analytics and Monitoring:Many CDNs provide real-time analytics and monitoring tools that allow website owners to track traffic patterns, analyze performance metrics, and gain insights into user behavior. These insights help optimize content delivery strategies and improve user experience.

Why do we need CDN?

Do you remember the slow dial-up speeds of the early 1990s? Even opening a static news webpage took a long time.

With the development of network technology, this situation has somewhat improved.

However, with the rapid advancement of network technology and the rapid increase in internet users, people have noticed a strange phenomenon: despite using higher bandwidth, watching videos, browsing webpages, or listening to music is still very slow. Why is that?

There are two main reasons, similar to driving a car, it's a problem of distance and bandwidth affecting the efficiency of user access.

Firstly, the issue of distance:

If we access a website or video from the US while in Beijing, the straight-line distance from China to the US is 14,000 kilometers. Even if the transmission speed of network cables is equivalent to 300,000 kilometers/second, the transmission delay is 467ms one way, totaling 934ms, and this is under ideal conditions.

The network connection between Beijing and the US is not a single cable but a complex mesh of many small networks, including the three major domestic operators in China and the secondary and tertiary networks used by home users. These networks require complex calculations during data transmission, similar to toll stations on highways, leading to network congestion and instability, making the real transmission speed far from reaching the speed of light. Therefore, when users in Beijing try to directly access video, live streams, or web resources in the US, they often experience buffering, mainly due to latency and instability during network transmission.

Secondly, in addition to the distance issue, there is also the problem of bandwidth.

The concept of bandwidth is not difficult to understand. Imagine when you are watching a video and the video server provides you with a 4Mbps bandwidth for a smooth viewing experience. However, when this number is multiplied by 10,000, meaning 10,000 people accessing the same video simultaneously, the bandwidth the server needs to provide increases dramatically to an astonishing 40,000Mbps, i.e., 40Gbps. This is why when the number of viewers surges, video playback often suffers from buffering. Few video providers can handle such huge bandwidth demands, which has been one of the challenges faced in the online video industry.

This scenario is comparable to the annual National Day holiday where everyone travels at the same time, but the highway cannot support so many vehicles traveling simultaneously, resulting in congestion.

Because distance and bandwidth determine the efficiency of a user's network access, CDN is specifically designed to address this issue.

Applications of CDN

1. Website Acceleration

Primarily targeting portal websites, and e-commerce platforms, such as Netease, Taobao, and similar sites. These websites often contain a large amount of static content files (text, images, etc.). CDNs can accelerate these files, significantly improving page response times and enhancing user experience.

1. File Download Acceleration

File download acceleration is a key function of CDNs commonly used for scenarios like software patch releases, game installers, etc. These files are often large in size, putting performance and bandwidth pressure on the origin server during downloads. By leveraging CDNs, this pressure can be effectively alleviated, enhancing client-side download efficiency.

1. Streaming Media Acceleration

Streaming media acceleration involves pushing media content to edge nodes closest to users, allowing users to access content locally, thus improving video playback quality and reducing traffic on the origin server network. Streaming media acceleration includes both live streaming and video-on-demand scenarios, suitable for various audio and video websites and applications like TikTok, iQIYI, etc.

1. Full-Site Acceleration

Primarily targeting sites with significant dynamic content, utilizing dynamic acceleration technologies such as intelligent routing and protocol optimization to enhance network efficiency from clients to the origin server, facilitating quick access to dynamic resources.

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