Content delivery (or distribution) networks (CDN’s) are computer systems which contain copies of data across several nodes of a network. The “nodes” of a distributed CDN are deployed in multiple locations – and often over several backbones. The nodes work together to satisfy end-user requests for content. CDN’s work in the background to move content in an effort to optimize the content delivery process.
Optimization can take the form of reducing bandwidth costs, improving end-user performance (reducing page load times and improving user experience), or increasing global availability of content. If the website you are responsible for does not currently use a CDN but there is an obvious need, WM’s Quick Start Guide to CDN’s provides some general information about what to consider when choosing a CDN.
There are many factors which come into play when choosing a CDN service. Price of course is an important element, but there are many, many other points of consideration.
Bandwidth: Understanding bandwidth needs and how many gigabytes of information will be transferred across the network is the single most important consideration to make. There is no single agreed upon transfer volume that warrants the use of a CDN, but if the volume is such that you are seeing complaints about download speed for videos, podcasts, images, etc., then a content delivery network is likely appropriate.
Network Performance: There are actually different kinds of content delivery networks which can make the selection process challenging. Internet based CDN’s such as Akamai route traffic from one PoP to the next getting your content onto the backbone of what ever ISP your end user is on. They then cache the content in that closest PoP so the next person in that region/ISP has the content already close to them. This is different than peering or private CDN’s such as EdgeCast, Level3 or Limelight Networks which place servers in regionalized locations. When a users requests content, files are delivered directly from the CDN to the end user network bypassing the Internet.
Business Side of CDN’s: There are several considerations that should be made to the efficiency and opportunities of the CDN for your particular business case. For example, what kind of support or training is provided? Is an annual contract required or can you use the CDN on a month-by-month basis? How long has the CDN been in business and how are they viewed by the general community of Internet professionals? Those seriously considering the use of a content delivery network will also need to ask about recent service outages.