A lot of ink and pixels have been spilled about the FCC‘s new rules for network neutrality. It’s impossible to comment sensibly yet about the actual proposal, since as far as I know it’s not been published anywhere, but the various news reports have left me confused about just what is being addressed. There are a number of different sorts of behavior that can result in performance differences to the end user; it isn’t always clear which are covered by the phrase “network neutrality”. Furthermore, some of these items involve direct, out of pocket expenses for a improvments in connectivity; this cost has to come out of someone’s wallet. The purpose of this post is to give a simplified (with luck, not too horribly oversimplified) explanation of the different issues here.

Note carefully that in this discussion, I am not trying to imply that network neutrality is good or bad. I simply don’t know of a less loaded term.

Before I start, I need to define a few terms. Roughly speaking, there are three types of users of the Internet: content, eyeballs, and content distribution networks. “Content” is what we read, watch, or listen to: news sites, movies, audio, etc. “Eyeballs” are consumers, the people who read, watch, or listen to content. (Yes, eyeballs can listen to MP3s. I never said that this post was anatomically correct.) Content distribution networks (CDNs) are a special form of content: to avoid chokepoints when sending out many copies of large files, such as images and movies, content providers send out single copies to CDNs and let the CDNs redistribute them. A CDN is just a set of data centers inside multiple networks.

Some networks, such as most cable ISPs, are mostly eyeballs. (Again, I’m oversimplifying; some cable ISPs do provide other services.) There are others that run hosting data centers; these are mostly content. Consumers wouldn’t sign up for Internet service if there was no content to watch; content providers wouldn’t be online if there were no consumers to profit from. This raises the first interesting question: who benefits more? That is, who should pay what percentage of the cost for an interconnection between a content network and an eyeball network?

The really big ISPs (sometimes known as “Tier 1” ISPs, though that phrase has become overly beloved by marketers), like AT&T and Verizon, have both content and eyeballs. When they interconnect, it’s called peering: they’re equals, peers, so they split the cost of the interconnection. Well, we think they split the cost; peering contracts are bilateral and confidential, so no one outside really knows. (For those of you who expect—or fear—discussion of BGP, autonomous systems, and the default-free zone, you can relax; that’s a level of detail that’s not really relevant here, so I won’t be going into those issues.)

The situation is different for smaller players. They’re not the equal of the Tier 1s, so they have to buy transit. That is, for a customer of a small ISP to reach a customer of a Tier 1, the ISP has to pay some Tier 1 for transit services to the rest of the Internet. (Yes, I said was simplifying things; I know it’s more complicated.)

So what does all this have to do with network neutrality? Let’s look at several cases. The simplest is intranetwork, where the eyeballs and two or more content providers are directly connected to the same ISP. Will the consumer get the same experience when viewing both content providers? If not, that’s generally considered to be a violation of network neutrality. That is, if the ISP is making decisions on how much of its bandwidth the two content providers can use, there’s a violation.

Note that I’ve assumed that all parties pay enough for their own bandwidth needs. An HD video stream takes about 6 Mbps; if I’m a content provider trying to send different video streams to 100 customers simultaneously, I’d better have (and pay for) at least 600 Mbps of bandwidth to the ISP. If I don’t, my customers will get lousy service, but that’s not discrimination, it’s physics. Sometimes, though, it’s hard to provide enough bandwidth. Wireless ISPs (who have sometimes claimed that network neutrality rules would be a hardship for them) are limited by spectrum; their internal networks may have ample capacity, but there’s only a certain amount they can push out to people’s phones. This isn’t discrimination, either—unless the ISP makes a choice about which content to favor.

Life gets more complicated when traffic is entering the eyeball network from outside. Eyeball networks are generally not Tier 1s; they buy transit. If there’s more demand for bandwidth than their current links can handle, they have three choices: they can increase their bandwidth to their transit providers, i.e., they can pay more for transit to connect their eyeballs to the content they want, they can selectively favor certain external content providers (which will give good service to some and poor service to others), or they can let everyone suffer equally. This last strategy leads to unhappy customers; the first strategy, though, implies higher costs that someone will have to pay. And the middle choice? That’s where network neutrality comes into play: who makes the decision?

Some content providers are willing to connect directly to eyeball ISPs. Must the eyeball ISP accept connection requests from all content sources? Who pays for the interconnection? Note that at a minimum, the eyeball ISP will need a dedicated router port, and someone has to pay for this port the physical link to connect it to the content source.

The other choice, for a content source facing congested links, is to deal with a CDN. This begs the question, though: CDNs need a presence (or more than one) on every eyeball ISP. Who pays for this presence? Does the eyeball ISP offer different terms to different CDNs, or turn some down?

If you’re still with me, you can see that “network neutrality” can cover many different sorts of behavior.

• Intra-network behavior, especially by wireless ISPs
• Transit links purchased by eyeball ISPs
• Direct connections between eyeball and content ISPs
• Connections by CDNs

and probably more. Which of these, if any, should be dealt with by regulation? Who should pay for added links or increased bandwidth?

These are not idle questions. In one case that’s been drawing a great deal of attention, Netflix has blamed “ISP trolls” like Comcast for discriminatory policies. Others, though, have claimed that Netflix deliberately used an ISP (Cogent) with a congested link to Comcast because it was cheaper for them. Did Netflix make this choice? If so, why wasn’t the link between Comast and the ISP upgraded? Was one party refusing to pay its proportionate share? (This is the sort of fact question that can’t be answered in the abstract, and I’m not trying to say who’s right or even what the facts are.)

If eyeballs are to get the content they want, some interconnection facilities will have to be upgraded, either by new links or by higher-speed links; this in turn means that someone will have to pay for the upgrades, possibly beyond the routine continual upgrades that all players on the Internet have to do. The network neutrality debate is about who makes the decision and under what criteria. Furthermore, the answers may be different for each of the cases I’ve outlined above. When the FCC’s rules come out, pay attention to all of these points and not just the buzzwords: it isn’t nearly as simple as “fast lanes for big companies” versus “government meddling in the free market”.