If you want proof that "the Internet" is not a single, contiguous nebulous of interconnected addresses, look no further than your home router. Long before there was a Web, the Internet's engineers devised the concept of subnets - a way for certain, restricted addresses to be resolved locally only. While your broadband modem may have a unique gateway address, all the PCs connected to that gateway certainly don't.

Content Delivery Networks (CDNs) are a fact of everyday existence; what's more, they're enabling CDN providers to build businesses around expedited delivery. Recently, we've covered new ways in which private CDNs may be leveraged to accelerate the whole Web, with a wealth of thus-far unexplored benefits. Comcast is building one of these CDNs, and is of course deploying it for its own consumer video services. That's been in the works for over four years, but now the discovery that Comcast's XFINITY on-demand TV service for Microsoft's Xbox 360 console will use Comcast's private CDN, has some tech news services praying for a new anti-net neutrality populist uproar to drive traffic.

"Not the Public Internet..."

The trigger was this notification about how XFINITY content would be delivered to Xbox devices on one of Comcast's FAQ pages, which marketers probably thought would be perceived as a benefit: "Since the content is being delivered over our private IP network and not the public Internet, it does not count against a customer's bandwidth cap. XFINITYTV.com and the XFINITY TV app stream content over the public Internet and count toward the customer's bandwidth cap."

That led to a warning about the very "survival of an Open Internet" from the advocacy group Public Knowledge. "This type of arrangement is exactly the type of situation the Federal Communications Commission's rules on the Open Internet were designed to prevent," stated the group's CEO, Gigi B. Sohn, "that an Internet Service Provider juggles the rules to give itself an advantage over a competitor. The Xbox 360 provides a number of video services to compete for customer dollars, yet only one service is not counted against the data cap: the one provided by Comcast."

It's a familiar sounding argument for the country's leading cable provider. In late 2010, when Level 3 Communications - which handles CDN service for Netflix - notified Comcast it would need even more bandwidth, Comcast responded by charging Level 3 a fee. The infrastructure provider balked, launching a PR campaign against the cable provider, accusing it of both threatening the open Internet and roadblocking Netflix, arguably its biggest competitor for on-demand video.

Meanwhile, Comcast was building its own content network (sometimes called CCDN) as a prospective solution to this problem, at least insofar as its own customers were concerned. As this article from Pipeline Magazine last November explains, a CDN wasn't just a convenient way for Comcast to deliver content to Xbox faster. It was actually the only way to do it, unless you consider building a separate string of servers just for Xbox customers a viable alternative. Comcast's CDN utilizes a multiscreen delivery platform developed by Alcatel-Lucent, literally called "thePlatform," called MPX, which manages scalability of Xfinity content to multiple classes of devices.

The article cites an Alcatel-Lucent source as saying a CDN is "absolutely crucial" to providing this class of service, because otherwise, devising separate streams for each individual client class - Xbox being just one - would result in quality-of-service degradation and slow video.

Is a CDN the Internet or Not?

That perspective was verified by engineers with the University of Massachusetts partnered with Akamai - the first CDN provider, and easily Level 3's biggest competitor. In a white paper on the subject (PDF available here), the team writes, "Inherent limitations in the Internet's architecture make it difficult to achieve desired levels of performance natively on the Internet. Designed as a best-effort network, the Internet provides no guarantees on end-to-end reliability or performance. On the contrary, wide-area Internet communications are subject to a number of bottlenecks that adversely impact performance, including latency, packet loss, network outages, inefficient protocols and inter-network friction. In addition, there are serious questions as to whether the Internet can scale to accommodate the demands of online video. Even short term projections show required capacity levels that are an order of magnitude greater than what we see on the Internet today. Distributing HD-quality programming to a global audience requires tens of petabits per second of capacity - an increase of several orders of magnitude."

The Akamai paper goes on to make this critical definition: "A delivery network provides enhanced reliability, performance, scalability and security that is not achievable by directly utilizing the underlying Internet." Indeed, one of the more competitive providers of CDN service to all customers is Amazon, with its CloudFront network.

The key to Comcast's CDN service, and what distinguishes it from its competitors at the moment, is that it's end-to-end. While it uses TCP/IP protocol, it's rather like a local loop that just happens to extend across North America. As such, data served over this wide-area-local-loop does not count against the 250 GB cap that Comcast has imposed since the fall of 2008.

But it's the notion that Comcast is bypassing the Internet for its own purposes that has already-skeptical customers raising warning flags.

Writes one Comcast customer on the company's forum, "An Xbox is just another computer, it isn't a cable box and it has no coax input. When someone requests a video on their Xbox it won't be metered by the headend and sent via RF like a cable box. It's IP streaming. Comcast's official shtick is that it's being sent over a private network and not the interwebs so they aren't being anti-competitive. This is what net neutrality advocates have been warning about. It appears Comcast is using its position as a content provider and ISP to unfairly limit the competition. Any other streaming IP service counts against the cap, but you can watch all the Comcast streaming IP you want with no penalty."

Public Knowledge's statement against Comcast was directed toward the FCC, in hopes that it might investigate the company's behavior. The advocacy group may be hoping the FCC still has room in its itinerary for revenge, particularly in light of the public shellacking it received in April 2010, when the D.C. Appeals Court ruled the FCC could not order Comcast not to throttle its traffic.

Comcast has been contacted for extended comment, which may be forthcoming.

Xfinity service is being offered by Microsoft as part of a new slate of additions to the Xbox Live Gold subscription service, including content from HBO GO and MLB.com. Xbox Live Gold subscriptions average about $5 per month.