A Content Delivery Network (CDN) is essentially a network of servers which deliver cached static content from your site to users of your site dependant on their location. Basically this works as an addition to your hosting as oppose to in place of it. So usually the process in a simplified way goes something like:
User goes to you site > they access the server you website is hosted on (Bluehost, GoDaddy etc.) > they arrive at your site
With a CDN in place the process goes something like:
User goes to your site > they access cached content from your site from a choice of several servers – using the server closest to their location > they arrive at your site
The only step that changes is the middle one and that’s where the most time is saved/lost. Usually the only place users can access your site is through the server your site is hosted on. Often this is on shared servers too, so there is already a low limit of how many users you can have on your site at any given time and it isn’t ideal for speed. Additionally, there is the lag as they have access to only one server located in one location. This leaves your site vulnerable to speed issues and crashes.
The huge advantages of the second example where a CDN technology is used, is that the site load time improves dramatically. Firstly all content is cached on the servers. This instantly improves the page load time. In a previous post we looked at the advantages of caching on your server and this dramatically decreases page load time. Then there is the location factor. Using a CDN will automatically use the nearest available server, which can save a considerable amount of time and ‘internet hops’ (the amount of routers passed before reaching its destination). A lot of servers are located abroad, often in the US which can obviously cause a delay if your site is based in the UK.
With a CDN you’ll have a server located in the UK, usually quite close to where you are located. Also it is hugely unlikely your site will ever crash due to the amount of servers available to users of your site. All sites want large volumes of traffic and should actually achieve this, you don’t want your server to buckle and lose those visitors. A CDN will prevent this.