VIDEO – What is a Content Delivery Network (CDN)?

5 min read

By: Ryan Sumner

Content delivery network (CDN): An overview

A content delivery network (CDN) is a distributed server network that accelerates internet content delivery to users based on their geographical location. The CDN can improve a users' website experience and reduce the number of bounced sessions.

In this quick overview video, I go through a scenario where a CDN helps make the website load time faster for globally distributed users.

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Video Transcript

What is a content delivery network (CDN)?

Hi, I'm Ryan Sumner, I'm a Chief Network Architect with IBM Cloud, and today I'm going help you answer—what is a content delivery network?

So, in short, a content delivery network (or CDN) is a service that accelerates internet content delivery. So, in other words, the main benefit of a CDN is that it makes your website faster.

Content Delivery Network (CDN)

The challenges presented by having users around the world

So, before I get into describing to you how it accomplishes that and some of the other benefits, first, I want to talk to you about some of the challenges that we have where we have users all around the world, but we don't have servers all around the world, and the experience that those users have due to that dynamic.

So, I got a simple diagram here showing a server hosted down in Dallas—this is my website—and then I have users all around the world.

Content Delivery Network (CDN)

So, in Sydney, I might have five, in London, I've got five, New York, I might have ten, and LA, I might have ten.

Content Delivery Network (CDN) users around the world

I’ve 30 users around the world that are accessing my server and my website down in Dallas.

So, let's follow a set of these users in their journey, and let's look at the users down in Sydney.

They make a request to the website, they've got an 8,600-mile hike to Dallas, and then an 8,600-mile hike back. The amount of time that that takes is usually measured in milliseconds, and just that round trip might be about a 170 milliseconds.

Content Delivery Network (CDN) response time

For our users up in London that might be about a 100 milliseconds.

Our users in New York City can probably experience about a 40-millisecond round-trip time.

And over in LA, about 30.

Content Delivery Network (CDN) response time2

So, as you can see, the further you’re away, the longer it takes and ultimately the slower the website will be for you.

Content delivery network (CDN) endpoints can provide an increase in speed

So, this is where the CDN comes into play, and this is how it actually accomplishes the increase in speed—which is by reducing the amount of distance between the user and the content, or the server providing the content.

So, what it does by doing that is it places these content delivery network endpoints in as many locations around the world as possible. And in our case, we're going to assume we've got one in just about every location where users exist.

Content Delivery Network (CDN) endpoints

CDNs retrieve content and distribute it around the world

So, now, when the user in Sydney, or London, or New York City, or LA tries to access some content, it's first retrieved by the content delivery network service and then distributed around the world. So, we have a single request down to the Dallas server. It's now then distributed all around the world.

And our users in London—now instead of going all the way to Dallas, they're able to retrieve that content directly from their closest geographical location, drastically reducing the amount of time that it takes to retrieve that content.

Content Delivery Network (CDN) retrieves content

Indirect benefits provided by CDNs

So, as you can see here, it's a very basic how a CDN is able to provide the benefits to the end user by reducing the amount of time that it takes to deliver the service. But what you're not seen here is an indirect benefit—the reduction in the amount of traffic that actually hits the Dallas server.

So, the indirect benefit is that you actually see a reduction in the load or a reduction in the amount of capacity that you need in Dallas to serve all these users.

Content Delivery Network (CDN) reduces load on the server

So, another indirect benefit—because there is much less validity and so much less stuff happening in Dallas, because all these users are not having to make these trips, and I'm also not having to communicate with users so far away. The Dallas environment may also see an increase in uptime.

Content Delivery Network (CDN) increases uptime

And then lastly because the users are not really directly communicating with the server down in Dallas, you have the indirect benefit of an increase in security through obscurity.

Content Delivery Network (CDN) increases security

So, it's pretty basic to understand how a CDN works—in the end, it provides a better benefit to the end user.

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