I will start this blog entry with a disclaimer: there are many definitions out there for CDN Federation, most are feasible but many are just not as practical and/or easy to implement as advertised. All you Trekkies that came here because of a Google alert about federation, sorry... we are talking about content delivery done seamlessly between two or more differing entities, not the United Federation of Planets.
To cut through all of the noise about CDN Federation, let's begin with the two traffic flow scenarios that make up CDN Federation. Outbound and Inbound which we will call Termination - and to be clear, this is not network packet flow which happens in both directions in either case, but rather content origination and location where content is consumed. The below diagrams will help illustrate what I mean.
Outbound CDN Federation - This is a widely deployed type of Federation and refers to when an Operator who owns some content, a network, and a bunch of subscribers needs to have greater reach for that content than the Operator's network allows. The Operator may also need some level of excess capacity or redundancy for their content and subscribers. This could be on a local or global level. The reasons for Federating are discussed a bit later, but for now you can think of Outbound Federation as being done in order to distribute content.
Termination or Inbound CDN Federation - This type of CDN Federation is done by Operators who are trying to localize and manage traffic. The traffic originates in a different operator's network but is consumed by the subscribers of the Operator deploying the Inbound Federation. Once again, the reasons for implementing this type of CDN Federation are discussed a bit later but for now you can think of Termination as being deployed to manage network traffic.
Now let's get to the reason as to why one would need Federation or Termination. The few practical reasons listed below are not applicable to everyone, but Operators will find at least one or more of these reasons appealing in order to become part of a Federation.
1. Global Reach (Outbound Federation) - this is the sexiest of the advertised reasons for Federating. Think of a perfect world where any Content Provider (CP) can reach any subscriber regardless of location. This is indeed a very good reason to federate your CDN. Much like your mobile phone service, where you can make calls and send text messages from pretty much anywhere to anyone. Federating allows roaming subscribers of a major cable operator or telecom to view their home Operator's content on any network, even a competitor. This roaming may not be necessarily global in nature like in the case of mobile phone, but more often perhaps down the street at your local coffee shop with a different ISP.
1. Maintenance, Overflow and Flash Crowd Handling (Outbound Federation) - No one really talks about this particular aspect of CDN Federation because well, it is not as exciting as global reach. But, it is probably the most useful part of Federation. This is generally done as additional on-demand capacity and is under a different administrative control than the Federating Operator. This CDN capacity is deployed in the same Operator's network or in the network of an adjacent Operator in the same geographical vicinity as the home Operator CDN is deployed. Sometimes this adjacent Operator can be a competitor. This type of Federation is done in order to handle scheduled or unscheduled maintenance and flash crowds created by major events.
2. Traffic Management and Localization (Termination) - When you are an operator with subscribers, your subscribers can request content that originates anywhere in the world. These subscribers also demand Quality of Experience (QoE) for the content they consume. This content, when coming from another operator, typically enters at a very expensive and capacity limited point in the Operator's network and then traverses the home network with very limited Operator control until it gets to the subscriber. This is expensive and hard to manage for the home Operator. This also can cause a poor QoE for the subscriber. Ultimately, nobody wins...
The solution to this challenge? Termination: bring the traffic deep into the Operator's network to cache it in strategic points, thus making it manageable. It is hard not to sound biased here, but the Federation has to be with someone who has a lot of content and more importantly has control of this content for legal and technical reasons.
With that said, and now that we are talking about Federation in the same context, the next blog post I will talk about the Global Reach portion of Federation and reasons some of the challenges associated with it.
Michael Kuperman is a senior director of Business Development at Akamai