A modern network architecture delivers better CDN performance
When content delivery networks (CDNs) were founded over 15 years ago, the internet was very different from what it is today. Content was uniform, internet access was wired (mostly through telephone lines with limited bandwidth), internet transit was expensive, and the interconnection between ISPs was limited. Naturally, the ideal topology was a highly distributed network with extensive last mile coverage. This meant having an astronomical number of servers and nodes. This might have worked for the internet of yesterday, but architecturally struggles to keep up with the demands of today’s internet.
Today, ISPs and carriers are well interconnected. Content is highly personalized. Internet access is now available from broadband ISPs via cable, fiber and wireless. A highly distributed network is no longer necessary in the modern internet architecture and has become a hindrance to efficient caching behavior. Verizon Digital Media Services’ CDN was architected to take advantage of the modern internet landscape. Instead of having thousands of small points of presence (PoPs) scattered throughout the globe, our strategically placed Super PoPs have massive computing power and high-bandwidth capacity at high-density internet connection points. This modern architecture delivers better CDN performance by achieving:
A better cache-hit ratio
When content, such as video, images or files is not cached inside the CDN, the edge server makes a request back to the origin server to obtain a copy of the content. This is called a “cache miss.” In a cache miss, the user does not enjoy the benefits of a CDN because the request is routed back to the origin server as if a CDN didn’t exist. When this happens, you incur increased costs associated with more origin load and bandwidth usage. A cache hit is when the CDN has the requested content in its cache available to the user from its edge server. The higher the cache hit, the better the user experience. In a highly distributed architecture with tens of thousands of PoPs, it means tens of thousands of cache misses are occurring before the content is fully loaded into a CDN. In today’s internet where content is extremely personalized, a highly distributed topology results in frequent cache misses that are detrimental to the user experience. A centralized topology with strategic PoP locations near Internet Exchange points results in more cache hits, not cache misses.
Horizontally scalable architecture.
We’ve engineered a horizontally scalable PoP architecture that load balances at the application layer. Even though there are hundreds of powerful servers within a Super PoP, an object is stored once within one of the servers. Layer 7 load balancing allows hundreds of servers to become one huge computing infrastructure within a Super PoP. This architecture allows each Super PoP to have a larger usable cache footprint to cache content, which translates to an average of a 95 percent cache hit ratio for our customers, a significantly higher figure compared to legacy CDNs.
Better server-to-delivery ratio.
A CDN must deliver content regardless of a surge in demand – expected or unexpected. Maintaining excess equipment and capacity just for the occasional spike in traffic is highly inefficient and very expensive. Cloud-based CDN services allow customers to meet a surge in demand without the unnecessary overhead. Furthermore, by concentrating computing capacity and having massive bandwidth, you get a better server-to-delivery ratio and the ability to handle massive spikes in traffic without degrading the user experience.
Centralized distribution combined with horizontal scaling provides for higher fault tolerance without affecting the user experience. Verizon Digital Media Services’ Edgecast CDN uses a proprietary design that creates redundancy to recover from hardware failures and has the capabilities to withstand attacks.
With a CDN, more isn’t always better; more points of presence are less efficient and can contribute to a high number of cache misses, increased points of failure, and greater complexity when making changes and updates. Verizon Digital Media Services operates differently. We’ve built a next-generation CDN with better architecture to provide a better cache-hit ratio, better server-to-delivery ratio and better reliability.