What is a Content Delivery Network (CDN)?

Learn about real time internet video delivery on global scale and what factors are crucial to achieve a reliable video stream.

Real time live video delivery

The internet is growing rapidly and still even increases its growing rate. While back in 2005 about 1 billion people used the internet on a daily basis, today there are 3.5 billion internet users that share 4 Exabytes (4,000,000,000 Gigabytes) of data every single day. To deliver such an amount of data to users around the world, a strong infrastructure is needed. This global infrastructure (also called backbone) consists of giant data centers and huge cables that connect all parts of the world into one great network. Some of the data centers form so called "sub networks". This happens if for example a company starts to build new data centers to provide delivery services for other big companies that generate high data traffic. These sub networks are called content delivery networks (or CDNs). Basically a CDN is nothing more than a bunch of globally distributed computers that are directly connected and move data from one end to another.

A good example of this is YouTube.There are more than 6 billion hours of video each month watched by YouTube users. As you can imagine (or... maybe you literally can't do this) this causes a very high amount of traffic. If YouTube would be hosted on just one simple machine within the internet, every single videos would be delivered from this one machine. Every data request would have to be handled by this single server instance.

Apart from the fact that this would be highly inefficient, think about latency.
What happens if a user requests data while being thousands of miles away from the server? Well, since a video will never change again after it is uploaded to YouTube, one could setup a second YouTube server and copy all the videos on this second machine. By doing so, both servers share information to number of requests and offload each other. At the same time, latency could be decreased for many people. And if this is possible, why not set up servers all around the globe?

 

For YouTube, this would mean a pile of extra work. Setting up, maintaining and managing all these servers would consume time, knowledge and of course money. So instead of building such a big delivery infrastructure itself, YouTube could just use an existing CDN because this is exactly what CDNs are made for.

Now all the videos that are viewed hundreds of thousands of times by viewers from all countries are already available right in front of them. Since the videos won't change again, we can just store them into the CDN keeping them ready to be served whenever a viewer sends a request. This technology is called caching and is one of the most efficient ways to reduce internet traffic. When streaming Video-On-Demand (VOD) problems are minimized at a fraction due to caching.

About 2 years ago a new streaming trend started growing and still grows rapidly. This new trend is a big threat for CDNs since it also causes high traffic but is almost completely resistant to caching: Live Video Streaming. Live video data is uncachable because of two reasons:

  • It changes every single second so there is no time to cache it
  • As soon as data is available it is almost irrelevant because it is real time

To make caching work for live OTT at any chance, very special server configurations are required. In fact these configurations are even harming a statically determined caching system. In order to make a CDN available for live streaming at all, a dedicated CDN with its main focus on live data would be required. But there is more! Most CDNs are working on a global scale. This means that a single CDN can consist of several thousands of caches which are connected in layers. There are few very strong caches which transfer their data to more, smaller caches. This is a good approach to build a resilient, reliable CDN for static content. However this multi-layer approach is a deal breaker for live content. Since the cache-to-cache transmission takes time, latency grows higher and higher.

Summarizing these facts, we now know what is needed for OTT live streaming:

  • A CDN that only focuses on live content
  • Few but very strong caches to reduce latency
  • A flat CDN structure without multiple caching layers

LiveGrid CDN is the world's first live-only content delivery network that exactly fits the needs to globally scale OTT live streaming. With our CDN solution we make live OTT affordable, feasible and scalable.

  • Alexander Schäfer
    CEO
  • Published: 11th July 2017

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