Using multiple CDNs is common practice among service providers. However, optimizing how they are used is a problem. Citrix’s ITM allows them to automate the management to get the best performance and the lowest cost.
Why service providers use more than one CDN
Many video service providers use multiple CDNs in the delivery of their service. There are many reasons the approach makes sense, including:
- Regional differences between CDN coverage
- Costs vary depending on the specific usage scenario
- Performance can differ significantly for any number of reasons.
To deliver excellent quality at the least cost is the primary goal and using multiple CDNs is often the best way to achieve it. Unfortunately, managing multiple CDNs is anything but simple and very few tools exist to help with the task. Providers often resort to rudimentary balancing approaches such as steering all traffic destined for iOS devices via one CDN and all Android via another.
One tool available to video providers is Citrix Intelligent Traffic Manager (ITM.) They can use it to automate the balancing of video stream load across multiple CDNs. It can also protect from CDN failure by automatically switching to another when problems occur. ITM is part of Citrix Cloud Services, and customers access it through a self-service web portal.
The lifeblood of a tool such as ITM is real-time data on the performance of the network.
Where the data comes from
According to Raj Gulani, Head of Product for ITM, the solution taps into 15 billion daily Internet performance metrics. The data comes from 900 million user sessions across 40,000 networks covering most countries in the world.
The data originates from a variety of different sensor sources, and many are not directly related to video. For example, Mr. Gulani says that Linkedin webpages on the social site are tagged and providing telemetry. That said, he says some video clients do provide performance data which is used by the system.
Performance isn’t the only criteria service providers need to take into account when picking the optimal CDN to use. ITM pulls hourly usage and billing data from CDNs, allowing it to use cost as another criterion. According to Mr. Gulania:
“The data allows for optimization between performance and contract commitments, managing against CDN spending commitments.”
The data gives the solution great coverage at the country and region level, though city-level coverage is on a case-by-case basis.
Integrating with the system
Once the integration with the video server is complete, the service provider can create scripts to define criteria to trigger a switch between CDNs. The scripts can include performance and cost criteria. For example, if latency exceeds 30 seconds or usage is approaching the contracted commitment for a given month.
How it works
Mr. Gulani says that when a stream is first initiated, ITM looks at it’s current CDN performance metrics and selects the most performaning CDN for the users’ ISP and geography. As streaming begins, ITM monitors its performance using its extensive network of sensors. The data is used to calculate the performance against the client’s needs defined in the script. When performance falls outside of the criteria, the stream is switched to another CDN. Once again, the performance is measured against the scripted criteria and move initiated if necessary.
To execute a switch in CDN, ITM manipulates DNS records, or is called as a web service. When a client clicks play on a video, a URL is assigned, which tells the video player on the device where the video server is that is streaming the video. By changing the DNS record, ITM can switch the CDN delivering the video without the client knowing anything has changed. Mr. Gulani says ITM makes billions of DNS transactions. The web service, or API, is used when customer’s wish to make mid-stream CDN selections, which is most popular during live events and long play videos such as video-on-demand movies.
Why it matters
Many video service providers use multiple CDNs for a variety of reasons.
There have been few tools available to help the operator select the optimal CDN to use.
Multi-CDN management tools are beginning to arrive that allow the operator to select the best CDN for a streaming task based on performance and cost.