Reference: Content delivery networks
Topic Last Modified: 2014-06-02
Summary: Explains what content delivery networks are and how Office 365 leverages them.
Using Content Delivery Networks (CDNs) helps keep Office 365 fast and reliable for end users. With CDNs, cloud services like Office 365 quickly download generic content, like icons, to your users’ browser when they’re using the service through a web client.
If you’re planning the network connectivity for your Office 365 setup, it’s helpful to understand how CDNs work. It is also important to understand that you can’t filter connectivity to the CDNs by IP address. We provide a best effort list of IPs for the services within Office 365, such as Exchange Online, Lync Online, and so on. You can find that guidance in our Office 365 URLs and IP address ranges page.
Downloading common things like icons over and over again can take up network bandwidth that can be better used for downloading important personal content, like email or documents. Because Office 365 uses an architecture that includes CDNs, the icons, scripts, and other generic content can be downloaded from servers closer to client computers, making the downloads faster. This means faster access to your personal content, which is securely stored in Office 365 datacenters.
CDNs are used by most enterprise cloud services. Cloud services like Office 365 have millions of customers downloading a mix of proprietary content (such as emails) and generic content (such as icons) at one time. It’s more efficient to put images everyone uses, like icons, as close to the user’s computer as possible. Yet, it isn’t practical for every cloud service to build CDN datacenters that store this generic content in every metropolitan area, or even in every major Internet hub around the world, so some of these CDNs are shared.
CDNs can be private or public. Private CDNs are owned and operated by a single company, and only that company’s applications and services can use it. Public CDNs are run by companies who lease usage to multiple companies. Depending on where you’re located, it might be most efficient for Office 365 to download generic images for you from a private CDN (that is, a CDN that Office 365 owns and runs), a public CDN, or a combination of the two.
The CDNs pull the files and images from the nearest Office 365 datacenter on a schedule. When users are accessing a cloud service, like reading email in Outlook Web App, the user’s browser attempts to retrieve the files and images from the Office 365 datacenter. Instead of spending the time and bandwidth delivering the files, Office 365 redirects the browser to the CDN. The CDN figures out the closest datacenter to the user’s browser and, using redirection, downloads the generic images from there. Using this CDN redirection is quick, and it saves users a lot of download time.
As a result of our fault tolerance configuration, how clients connect needs a little more explanation than is the scope of this topic. Please refer to our visual guide on Reference: Client connectivity.