Content Delivery Networks — What is a CDN?

Content delivery networks, or CDNs, make online experiences faster and more reliable by delivering content closer to users.

What is a CDN?

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 digitized can be delivered through a content delivery network.

What is a CDN host?

Although CDNs aren’t web hosts and don’t deliver items over the last mile to consumers, content delivery network servers are geographically distributed to cache content closer to users and their ISPs wherever they are in the world. This temporary content storage at the network edge makes it possible to reduce latency and deliver the same content to multiple users for more efficient access.

For network operators, also known as wireless service providers or mobile network carriers, that are struggling to keep up with the never-ending demand for online video, a CDN hosting platform can be a highly effective and cost-efficient solution to stay competitive. A content delivery network can enable operators to provide a fast, secure, reliable online experience with the consistent quality that people expect on every web-enabled device.

Why is a CDN needed?

For over 20 years, CDNs have formed the unseen backbone of the internet — delivering online content for shopping, banking, healthcare, and other businesses quickly and at scale.

Without CDNs, with their ability to replicate and store information from origin servers and then bring digital content close to where users access the web, the internet might be slowed to a crawl.

You may not realize it, but if you’ve done almost anything online, a CDN has probably helped provide you with a fast, reliable, and consistent experience. Here’s a simple example of how content delivery networks manage traffic behind the scenes to make that happen:

A CDN balances overall traffic to give everyone accessing internet content the best web experience possible. Think about it like routing traffic in the real world. There may be one route that’s usually the fastest from point A to point B if no other cars take it — but if it starts getting congested, it’s better for everyone if the traffic gets spread out over a few different routes. That may mean that you get sent on a roadway that’s a few minutes longer (or microseconds, when scaled to internet speeds) but you don’t get stuck in the traffic jam that’s forming on the route that is typically the fastest. It may also mean that you get sent on that fastest regular route, but without getting bogged down in traffic, because other cars are being sent on longer paths. So, it’s not a matter of slowing down, it’s about load-balancing and fully using all available resources.

The fact is, without CDNs, we’d all be stuck in traffic jams a lot more often when surfing the web. 

Who uses CDNs?

Almost everyone that accesses the web uses a CDN. They were created to provide a faster and more reliable experience for people accessing the internet. They are used by the content and application owners and network service providers that supply those benefits to their customers.

CDNs for End Users

Websites and web applications delivered through a CDN experience faster page loads, faster transactions, and a more consistent online experience. However, people may have no idea they are connecting through a content delivery network as they enjoy its benefits, because the technology works behind the scenes. They simply receive what they requested from their ISP or mobile provider.

CDNs for content owners

Content and application owners — including ecommerce sites, media properties, and cloud computing companies — use CDNs to improve customer experiences, lower abandonment rates, increase ad impressions, improve conversion rates, and strengthen customer loyalty. Using a content delivery network can also improve web security, for instance by helping to absorb and mitigate a distributed denial-of-service (DDoS) attack.

CDNs for Network Service Providers

With the explosive growth of online streaming and other rich media services and higher user expectations about web performance across multiple device types, many of today’s network service providers are finding it necessary to deploy their own content distribution networks. For network operators, deploying a content delivery network can reduce subscriber churn, facilitate the development of value-added services, reduce traffic on the core network, and enable operators to sell CDN services to enterprises and third-party content owners.

One of the biggest benefits of a CDN is offload. By responding to a request for web content with a cached version in closer physical and network proximity to the end user — instead of from the server where the content originates — a CDN offloads traffic from content servers and improves the web experience. This means that content can stay within the network operator’s network and reduce the need to engage in peering with other networks or navigating the broader internet to deliver information.

What are the benefits of a CDN?

CDNs carry a large portion of the world’s internet traffic. They help solve the toughest challenges of delivering content over the internet. Businesses from small and medium content providers to the world’s large corporations use content delivery networks to provide a seamless web experience to their customers.

Because the internet was not originally designed to handle the demands of massive amounts of data, live high-definition video, flash sales, and large downloads, CDNs were built to make the internet work better. They help to securely deliver media at scale and enable all of the connected experiences that are part of daily life for most of us today. 


By providing solutions for performance, availability, security, and intelligence, CDNs help the world’s top companies and organizations do business successfully online


Performance

Performance is the difference between a click giving you immediate access to new content and a click followed by a seven-second wait while a page loads or a video buffers. Buffering is that wait time, symbolized by a familiar swirling circle icon on screen, that happens when the internet connection provided by an ISP can’t supply data fast enough.

How does it work? When requested content is cached (pre-saved) by a CDN’s servers, an end user’s ISP or mobile provider gets that content by connecting to a server on the CDN’s network, rather than waiting for their request to go directly to the origin. An origin server, where the content you are trying to access lives, may be far away from your physical location. If so, a CDN will bring that content closer to you, improving speed and performance. For example, let’s say that Fashion House X (FHX) from Milan, Italy, releases its new lineup for online orders. Fashion lovers in New York, Paris, Rio De Janeiro, and Tokyo all go online to make their orders. If FHX isn’t using a cloud content management system, the request from each end user must go all the way to Milan and back. However, if FHX uses a CDN and has preloaded its content across the CDN, each user can access the new content from servers directly in their city, saving their data hundreds or thousands of miles in round-trip time. 

If the content isn’t already pre-saved, the CDN uses its programmed knowledge of the necessary connections to overcome any challenges. Advanced CDNs use additional technologies that resolve any issues in the delivery of dynamic, or uncacheable, content and to determine the appropriate type of content to deliver to different devices. 

All of this means that, when using a CDN, content providers can deliver fast, quality web experiences to all their end users; no matter what location, browser, device, or network they’re connecting from. Web pages render more quickly, video buffering time is reduced, and users stay more engaged.

Availability

Availability means that content remains accessible to end users even during periods of excessive user traffic when many people are accessing content at the same time or if there are server outages in some parts of the internet. 

When traffic loads peak at millions of requests per second, even the most powerful servers are put to the test. Without a content delivery network, all this traffic must be absorbed by a content provider’s infrastructure. This can cause failures and poor end user experiences. The widely distributed server infrastructure offered by CDNs is designed to alleviate these issues. Advanced CDNs, with their highly distributed architecture and massive server platforms, can absorb tens of Tbps of traffic and make it possible for content providers to stay available to even larger user bases.

As an example, let’s return to FHX in Milan. Its brand is beloved by millions of fashion lovers, and its new lineup generates a lot of excitement. At the moment of launch, fashion lovers from all over the world go online to FHX’s website at the same moment. If FHX is not using a CDN, all of those users would hit its origin server at the same time, causing it to fail. However, if FHX is using a CDN, all of that traffic will be served across the CDN’s hundreds of thousands of servers, keeping FHX’s origin from failing and delivering a quality experience to fashion lovers across the globe. 

Security

As the volume of high-value data and transactions on the internet continues to grow, so do the forces of attackers looking to exploit it. Attacks by malicious actors can cost organizations big money. Along with crimes committed by malicious insiders, DDoS and web-based attacks have been found to be the costliest. 

Denial-of-service attacks and web-based exploits (SQL injection, cross-site scripting, and local or remote file-inclusion attacks) are becoming more common. These attacks are increasingly launched in conjunction using a DDoS attack to divert attention while causing more serious damage with other exploits. In both types of attacks, it is often difficult to distinguish bad traffic from legitimate traffic, and attack strategies continue to evolve rapidly over time, requiring significant dedicated security resources in order to stay up to date on mitigation strategies. 

Given the increasing volatility of the internet threat landscape, helping to secure websites is a critical CDN requirement. Today’s most advanced content delivery networks have made information security a core competency, providing unique cloud-based solutions. CDNs should protect content providers and users by mitigating against a wide array of attacks without malicious entities ever compromising delivery and availability.

Intelligence

As carriers of nearly half of the world’s internet traffic, CDN providers generate vast amounts of data about end-user connectivity, device types, and browsing experiences across the globe. They can use this data to help their customers, giving them critical, actionable insights, and intelligence into their user base. These services may include real-user monitoring and media analytics to measure end-user engagement with web content and cloud security intelligence to keep track of online threats.

Cloud versus CDN

The modern digital experience has expanded how companies deploy their content. CDNs and cloud computing were developed to address challenges the demand for web content and applications create in terms of performance and scalability. But how are they different?

Cloud

Cloud computing environments store information on internet servers instead of on your computer’s hard drive. For end users, this can be a convenient and reliable means for things like web-based email, file storage, file sharing, and backing up data. It’s also how people readily access web applications like social media platforms. Cloud environments consist of hundreds of PoPs with servers centralized in regional locations.

For businesses, the cloud offers lower upfront costs and the ability to scale application infrastructure as needed, expand into new geographies without having to invest in costly new infrastructure, and take advantage of related cloud services to build the latest digital experiences or enterprise applications. 

While the cloud can offer many benefits, organizations often experience unexpected costs when building applications in or migrating applications to the cloud. The dynamic nature of cloud migration projects can make it difficult to maintain performance and availability of digital experiences. 

CDN

A CDN is a network of servers that distributes content from an “origin” server throughout the world by caching content close to where each end user is accessing the internet via a web-enabled device. The content they request is first stored on the origin server and is then replicated and stored elsewhere as needed. By caching content physically close to where a user is and reducing the distance it has to travel, latency is reduced. This process also decreases stress on origin servers by distributing the load geographically across multiple servers.

Some people refer to content delivery networks as “the edge.” The edge is where the physical and digital world meet and interact at the network perimeter. With thousands of PoPs widely distributed around the globe and unmatched capacity and scale, CDNs provide closer proximity to end users. 

This means wherever you are in the world — using your mobile phone, tablet, computer, or other internet-enabled device — the content you want to access will load more quickly. You could be watching a video at home on the couch or checking in to your flight on another continent, and get the same seamless digital experience because of a content delivery network.

CDN Solutions from Akamai, the latest in edge delivery

Akamai’s CDN services were born from a challenge posed by internet founder Tim Berners-Lee, to solve what came to be known as the “world wide wait.” We pioneered edge computing more than 20 years ago by developing sophisticated new techniques to route web traffic, getting content from centrally located servers to early internet users faster. Today, the world’s biggest brands trust Akamai’s solutions and expertise to protect and deliver their digital experiences.

No matter the type of content — from websites, apps, APIs, video, or software — our comprehensive set of content delivery solutions is designed to deliver amazing digital experiences for every user, regardless of location, device, or network. 

Akamai has an unmatched global network capacity of 300+ Tbps and is unparalleled at scale with over 4,200 locations and upwards of 1,400 networks that span 135 countries. With the largest edge delivery platform, we see more of what’s happening on the internet. This means we can deftly avoid bottlenecks and defend at the edge. 

Automated acceleration to deliver the best website and mobile app experiences imaginable

Today’s users demand visually engaging, personalized experiences that are fast on every device, all the time. To deliver on customer expectations, digital businesses craft increasingly complex applications that are loaded with high-res images, videos, personalization, and other third-party content. The outcome can be very costly to optimize, operate, and maintain. The Akamai Ion intelligent performance automation and controls continuously analyze, optimize, and accelerate web and mobile app experiences.

High-quality video playback experiences to any screen

Online audiences may not know, or care, about the challenges you face when it comes to delivering online video. They expect fantastic video playback at all times, despite the many online content delivery challenges that stand in your way. Adaptive Media Delivery is optimized to provide consistent, high-quality video playback experiences across any screen to growing online audiences.

Seamless download delivery

End users expect frictionless download experiences, combining fast downloads and nearly instant updates. An effective and reliable content distribution and download strategy is a key factor in maximizing download completion rates, customer satisfaction, and revenue — whether they are downloading software, an application, a game, or a security patch across the device landscape. Download Delivery is a reliable, high-performance solution optimized to deliver large, file-based content over the internet. 

API Acceleration

APIs play a critical role in today’s fast-paced digital environment where connection speeds are measured in milliseconds. It’s becoming increasingly challenging to meet user expectations as the number of API requests are growing at a relentless pace and with frequent and sudden spikes in demand. When public-facing APIs aren’t delivered quickly, this can lead to poor user experiences, revenue loss, and downtime. Working with a partner that can take concerns about reliability, scalability, and performance out of the equation is a necessity.

API Acceleration is optimized for API delivery and other small payload traffic to enable fast and engaging user experiences across apps and sites. The solution offloads requests from origin infrastructures and provides predictable high performance for large volumes of XML, JSON, and other small transactional and programmatic traffic types critical to application success.