A couple of days ago, an anonymous individual identifying themselves as “Backdoor Santa” published some graphs showing that Comcast, a major US Internet Service Provider, runs it’s transit links at capacity for much of the day. This sort of tactic has depressing implications for any attempt to legislate for Net Neutrality, although I shall need to go through some basics to explain why.

As a mid-level ISP, there are three groups of people who you send traffic to and from. These are your customers, your peers and your transit providers. Customers, logically, pay you to carry their traffic. More customers means more money although for many ISPs, customers who buy bandwidth off you are probably not particularly profitable compared to those renting servers or space in a data centre.

Next come your peers – people who you are happy to exchange traffic with for free. (Or at least for no more than the cost of running a few fibres or other circuits between your networks) There is a careful balance to be struck here as fibre between sites and ports on network equipment cost money. This means there is a certain minimum amount of traffic that needs to exist between the networks before it’s worth doing, plus you also don’t want to peer with someone when you’re in London, New York and San Jose but they’re only in London as you’ll be paying for all the expensive international bandwidth.

Finally, if you have traffic that’s destined for somewhere that’s not a customer or reachable for free via a peer, you need to have paid transit. Some companies are so big that they don’t have to pay anyone else to take their traffic because they can reach everyone else either as a customer or via peering. The number of such ISPs varies, but is usually less than a dozen.

So why do Comcast run their transit links so congested as to cause problems? Won’t their customers complain? Well, yes but as some sites will run fast it will just be those sites that run slow that seem to have the problem and they’re big enough to get away with this. If someone providing content, say Amazon or Apple, want to peer with them in order to make the site faster they either say “Sorry, No, you don’t meet our requirements” or put the peering on a link running overcapacity too. The result is that those providers then need to pay Comcast as a customer in order to get decent service. If they don’t, Comcast users will go to their competitors for service.

This is definitely not “Net Neutrality” and something that should be stopped – if indeed it does occur in this country – as it is abuse of a dominant market position. Sadly, there is no prioritisation of traffic involved anywhere which is the usual topic up for discussion in neutrality debates. I do not know of any way of separating out genuine engineering requirements and complicated calculations on the cost vs. benefit of peering from this sort of activity.