CDN Performance: The Content Delivery "Network Of Networks"

Content delivery networks (CDNs) are well-established as a necessary component of today’s digital video delivery strategy. Closing the physical distance between the server and the end-user is a great way to protect the quality of end-user playback and security of the video files themselves. With lots of CDNs out there, all with different footprints and points of presence (“POPs”), it’s becoming increasingly common for content creators to adopt a multi-CDN approach, which allows them to deploy a best-case “network of networks” to improve performance across the board.

The benefits of a multi-CDN approach go beyond simple math:

  • The “simple math” part: more POPs are storing content closer to more viewers, resulting in the uniformly high-quality playback experience that audiences expect.
  • The “even better” part: with the right tools, traffic can be optimized so that CDN performance can be strategically leveraged based on the needs of each viewing experience.

Of course, the trick is to identify the best CDN for each playback experience.


There are several reasons why a business would switch traffic between multiple CDNs.

The fundamental advantage is redundancy: if there’s an issue with one network, a “detour” that employs a different CDN provides a redundant path to get the content delivered on time. Some might be driven by specific business rules, such as diverting traffic to a different CDN once the traffic hits a certain level, or based on other criteria such as contractual usage limits or other requirements. Some CDN routing rules can be completely based on cost-effectiveness, choosing a path from origin to device primarily on price.

Whether the reasons for a multi-CDN approach are traffic-based or rules-based, the best solutions are built to respond to real-time, quality of experience, emphasizing quality measures over any other metric. Optimizing your delivery with a service that provides transparency through proactive, automated, and real-time control over your delivery decision-making protects your audience’s quality of experience and extracts the most value out of your entire delivery path.


Ultimately, the single best litmus test of your service’s CDN performance is the experience at the individual user level. It presents a serious measurement challenge: how does a provider really measure playback quality? Not just in theory, but in practical, “that-customer-at-that-time” terms, across devices, platforms, and geographies?

Initially, measurement approaches utilized small static test object downloads and not the actual video stream itself. The test object measurements were aggregated together to paint a generalized, high-level picture of how well a CDN was performing. In today’s age of server tuning by application, most video is played back off of dedicated video servers and not servers used for test object downloads. Consequently, the resulting CDN performance score may not directly relate to your video streaming performance. Fortunately, with advances in technology, there are more evolved approaches today that result in measurable improvements for audiences.


Drilling down to individual viewer measurements is a core strength of DLVR, our new CDN optimization partner (you can read more about them here). To get there, DLVR continually measures actual video streams being delivered to end users. As a CDN moves video content through the network to intended destinations, the measurements from different streams can be aggregated into a more accurate performance snapshot. On top of that, customer experience metrics such as buffering and bit rate can now be rolled into a deeper analysis that can have a much stronger impact on quality improvement efforts.  It results in a tailored switching protocol that’s informed and driven by actual viewing experiences. Because the measurements are stream-based and not tag-based, the only way a CDN can demonstrate better performance is…by demonstrating better performance. It’s better for the audience, which of course is better for content creators and providers as well.     

Learn how to use Comcast CDN and DLVR together to easily enable a multi-CDN strategy and drive down costs based on business rules.

For more about multi-CDN delivery, please download our free ebook, Video To The CDNth Degree.