In the world of content distribution networks, A is for Akamai. What about the rest? Is B for BitGravity, or maybe BitTorrent because of the potential impact of peer-to-peer technology on CDNs? Is C for content? I don't think so. I think it's for carrier or maybe cloud -- and in either case, the "C change" is potentially a major one for the CDN world.

Content distribution networks evolved as a means of getting traffic off the Internet backbone, where peering delay and the intricacies of peering agreements threaten to make any highly visual Web site (much less content) into a PR nightmare for the owner. A CDN acts as a local cache for key content elements; with a local cache, elements load faster and use less core bandwidth. The process works best if there's a lot of repetitive demand for a relatively contained list of content and the content in demand isn't available locally through some other means. The reason a P2P network could affect CDNs is that it offers another local place where content might be available.

P2P technology probably isn't much of a risk to CDNs, however, because there's no assurance that P2P-streamed content would be of the quality that site owners want. What would create a bigger threat is a metro content-storage alternative from a credible provider with high performance and volumes of storage. That is exactly what telco TV, telco CDNs, and telco cloud computing are threatening to provide -- and soon.

If you think about it, anything that hosts storage, content, computing or applications can be considered a form of cloud computing because it provides a network-addressable resource. A big data center in a metro area used to support video on demand for a cable company or telco would serve just fine as a storage point for other content, including the stuff that's hosted on CDNs. Not only that, it probably would offer pretty good performance and economies of scale in content storage and delivery.

That may be why AT&T has announced its own CDN plans, and why other telcos worldwide also are looking hard at the CDN opportunity. If you have to build data centers, storage farms and fat connections between them and your metro network, you may as well sell some services from the new infrastructure you've built and get into the CDN business. Nevertheless, costs aren't the only reason some of the big telcos and cable companies are looking at rolling out their own CDNs. There are some new issues in the CDN world these operators believe need special attention.

One big issue is the handling of interactivity. In the old days, content served from CDNs was static: You pushed it out when it was called for, and you forgot it. With highly interactive pages and with more complex video, there is some need to support interactivity to make it possible to support Web 2.0-style dialog or to pause and play, rewind, or fast-forward video content. Interactivity also may be needed to allow for selection and insertion of ads based on the viewer's demographics.