A content delivery network (CDN) is a group of geographically distributed servers that speed up the delivery of web content by bringing it closer to where users are. Data centers across the globe use caching, a process that temporarily stores copies of files, so that you can access internet content from a web-enabled device or browser more quickly through a server near you. CDNs cache content like web pages, images, and video in proxy servers near to your physical location. This allows you to do things like watch a movie, download software, check your bank balance, post on social media, or make purchases, without having to wait for content to load.

You could think of a CDN like an ATM. Having a cash machine on practically every corner makes it fast and efficient to get money. There’s no wait time in long bank lines, and the ATMs are placed in many convenient locations for immediate access.

CDN services were created to solve the problem of network congestion caused by delivering rich web content, such as graphics and video over the internet — much like a traffic jam. Getting content from centrally located servers to individual users simply took too long. CDNs have now grown to include everything from text, graphics, scripts, and media files to software downloads, documents, portals, ecommerce, live streaming media, on-demand video streaming media, and social media sites.

CDNs can also provide websites with increased protection against malicious actors and security concerns like distributed denial-of-service (DDoS) attacks.

What is an example of a CDN?

A large portion of all internet content is delivered through CDNs. Here is a simple example:

If you were in New York and wanted to view the website of your favorite store in London that’s hosted on a server in the UK, you would experience slow content load times if the request had to travel all the way across the Atlantic Ocean. To remedy this, a CDN would store a cached version of the London website content in multiple geographical locations around the world, also called “points of presence” (PoPs). These PoPs contain their own caching servers and are responsible for delivering that content close to where you’re located in New York. Content delivered from a server closest to your physical location gives you a faster, high-performance web experience.

How does a CDN work?

The mission of a CDN is to reduce latency. Latency is that annoying delay you experience when trying to access a web page or video stream before it fully loads on your device. Although measured in milliseconds, it can feel like forever, and may even result in a load error or time-out. Some content delivery networks alleviate latency by reducing the physical distance that the content needs to travel to reach you. Therefore, larger, more widely distributed CDNs are able to deliver web content more quickly and reliably by putting the content as close to the end-user as possible.

Let’s say it’s the weekend and you want to kick back and stream the latest Hollywood movie release — the CDN finds an optimal server on its network to serve up that video. Usually, that will be the server closest to your physical location. The media files will be cached and remain on that content delivery network server for other user requests in the same geographic area. If the content you requested is unavailable or outdated, the CDN service will store the newly fetched content to serve any future requests.

While the delivery of website content is a common use for CDNs, it’s not their only function. In fact, CDNs deliver a wide variety of content that includes: 4K and HD-quality video, audio streams, software downloads such as apps, games, and OS updates, and much more. Potentially any data that can be digitised can be delivered through a content delivery network.