What is a content delivery network (CDN)?

What is a content delivery network (CDN)?

This article provides a basic overview of how content delivery network (CDN) services work and gives definitions for specific terms commonly associated with CDN. 


A content delivery network (CDN) is an interconnected system of servers that are strategically placed in multiple geographic locations around the world. A CDN improves load times for your website and provides faster delivery of content to numerous users by duplicating the content on multiple servers known as edge servers, and directing the content according a user’s geographic location.


Asset:  A resource that contains header information and a body that can be served to a client. Examples of assets are an image, a video, javascript, or a CSS  file.

CDN URL This is the general term for any URL that directly references our CDN domain. This URL is typically used to request assets via the CDN.

Cached Asset:  An asset that is cached on an edge server in a POP (points of presence).

Customer:  In the context of CDN, "customer" refers to individuals who are visiting a website, therefore instructing a Web server to retrieve content.

Data Delivery Platform: The infrastructure of servers and devices that are distributed across a worldwide network of POPs, which are configured for the express purpose of efficiently delivering a specific type of data from an origin point to clients.

Edge CNAME URL A URL that uses an Edge CNAME and a CNAME record to mask the CDN URL,  that is automatically generated after configuring a customer origin. By using an Edge CNAME URL, you are making the URL to access your content more meaningful and user-friendly than a CDN URL .

Edge Server:  A server on a CDN network that resides in a strategically placed geographic location, and requests data or assets from an origin server, and then serves the assets to the client requesting them.

Platform:  In the context of EdgeCast CDN, "platform" or "data delivery platform" refers to the infrastructure of dedicated servers and devices that have been distributed across a network of worldwide POPs which have been configured specifically to secure and deliver content.

POP (point-of-presence):  A POP is one of many worldwide locations on the CDN through which clients can request and receive assets.

Origin servers

An origin server is the server where your assets are stored. Before you can access server assets from the CDN, assets must be retrieved from their origin server. There are two types of origin servers: customer origin servers and CDN origin servers. You can take advantage of multiple origin servers to fulfill your CDN data delivery needs. Each type of origin server is described below.

Customer origin server

A customer origin server is a web server that is external to the CDN, while a CDN origin server is a dedicated CDN storage server from which we allow customers to serve assets.

The customer origin server stores content on the web server where your service with Nexcess resides. The main advantage of a customer origin server is that you do not have to transfer data to another server. All of your data will remain on your Nexcess server and the CDN will do the rest of the work. This saves you the time it takes to manually upload and maintain data on the CDN.

Attention: "Customer origin" is synonymous with "client origin."

CDN origin server

CDN origin refers to the content stored on the a storage server inside the CDN network and served to customers by a CDN edge server. The main advantage of a CDN origin is the data is stored on a server inside the CDN network, which can offer quicker load times initially, but requires more maintenance as you have to upload data to the CDN manually with FTP.

Data delivery platforms

With an EdgeCast CDN provided by Nexcess, data can be delivered over multiple specialized platforms.

The most commonly used data delivery platforms in an EdgeCast CDN are HTTP large and HTTP small. The following sections describe each of these platforms.

HTTP small

The HTTP small platform is optimized to serve small or less than 300 kB and frequently used content, such as JavaScript, CSS, and thumbnail image files. Since these assets are served directly from RAM, customers can experience faster delivery. The HTTP small delivery platform is ideal for websites using ad serving, eCommerce, and photo sharing galleries.

The HTTP small platform stores and serves cached content straight from RAM. This decreases overall load time as it does not require the edge server to spend time waiting for files from the disk.

HTTP large

Although the HTTP large platform can serve any type of asset over the HTTP/HTTPS protocol, it specializes in the delivery of large assets that exceed 300 kB in size, as well as those that are not frequently downloaded. The typical applications for this platform includes the delivery of videos, high resolution images, audio content, and downloadable products from eCommerce sites.

Refer to the How to configure a CDN customer origin server for instructions on configuring either delivery platform.

Attention:  Selecting the wrong platform for the type of content that you want to serve can cause problems for your website. Therefore, it is very important that you choose the correct platform for the type of content that you are going to serve.

Data retrieval, delivery, and caching

If a client requests an asset that is not currently cached on the POP handling the request or if the cached version of the asset is outdated, a new version will need to be retrieved from either the CDN or customer origin server. The edge server on the respective POP will request the asset from the CDN or Customer Origin server. Once the POP starts receiving the asset from the origin server, the edge server will immediately start delivering it to the requestor. Once the entire asset has been retrieved from the origin server, it will be cached on that POP. By default, the Cache-Control and Expires headers that are generated by the origin server are associated with that asset. If header information is missing for that asset or not defined, then the default max-age of that asset will be 7 days. This means that a cached version of that asset will be stored on the POP and it will be treated as fresh content for 7 days.

Configuring your Nexcess CDN

You can configure your CDN to work with virtually every site, web application, or CMS . Refer to the following articles for information on setting up CDN for WordPress, CDN for Magento, as well as a general guide that can be used with static sites:

For 24-hour assistance any day of the year, contact our Support Team by email or through the Client Portal.

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