First-generation CDNs use a highly distributed edge model, and include companies like Akamai and Sandpiper Networks (whose acquisiton chain goes Digital Island, Exodus, Savvis, Level 3).

Second-generation CDNs basically try to achieve most of the performance of a first-generation CDN without needing hundreds of POPs, aiming for just a few dozen locations. Speedera (eventually acquired by Akamai) is the best example of a CDN of this type.

Third-generation CDNs follow a megaPOP model — two or three dozen huge points of presence, which they hope will be highly peered. Limelight, VitalStream (acquired by Internap), and the new entrants of the past two years are pretty much all megaPOP CDNs.

Fourth-generation CDNs are very different. They are a shift towards a more software-oriented model, and thus, these companies own limited (or even no) delivery assets themselves. Some of these are not (and will not be) so much CDNs themselves, as platforms that reside in the CDN ecosystem, or CDN enablers. Velocix (for their Metro product) and MediaMelon both reside in the fourth-generation space.

That gets us to the morning’s interesting announcement.

Conviva has come out of stealth mode with a powerhouse customer announcement — NBC Universal. Conviva is not a CDN in the traditional sense, but they’re part of the ecosystem for Internet video. Rather than owning delivery assets themselves, they’ve got a pure-play SaaS solution — a platform that can arbitrage resources from multiple content sources (multiple CDNs, data centers, etc.), as well as offer value-added services like real-time analytics and integration capabilities across those multiple sources. (From an ecosystem perspective, the closest analogue is probably Move Networks.)

What makes Conviva immediately notable is their ability to do real-time monitoring of the performance of every individual delivery, and seamlessly switch sources midway through playing a video, driven by metrics and business rules, thus allowing the customer to deliver consistently good-enough performance (i.e., a target of no buffering or other degradation) at the lowest price point, i.e., cost-arbitraged QoS.

I’ve been writing about the customer desire for control and the rise of the fourth-generation software “CDN” since last year. Conviva takes full advantage of the overlay model. I’d rate the significance of this launch on par with that of Netli’s (back in 2003), although obviously in a very different way.

Because it’s a particularly important launch, I know it’s going to be of substantial interest to Gartner’s Invest clients, and likely of significant interest to our media and telecommunications industry clients. As such, I’m refraining from blogging a detailed description or analysis of the company’s technology and strategy, its likely impact to the rest of the video delivery ecosystem (which goes beyond the CDNs themselves), and the more general impact of the conceptual shift that’s taking place with fourth-generation CDNs. If you have inquiry access, please feel free to use it. A note to clients will be published soon.

(Disclaimer: I was pre-briefed on this, and I am quoted in Conviva’s press release. As I almost always do, I wrote my own quote, rather than letting words be put in my mouth. As with all Gartner quotes in press releases, it is a statement about the market, and no endorsement of the vendor is implied.)