Niels is in a position to know what his network does. You are in a position to know what your network does.
My guess is Comcast requires a contract with everyone, meaning your peering bits are mostly (all?) contracted.
I know Akamai does not require a contract, and will only sign if the other side requires it. (This is not a secret.) My guess is they have a lot more un-contracted peering bits than Comcast.
However, let’s look at the basic premise here. A handful of networks (50? 100? 200?) on the Internet require contracts with everyone. And if we are being honest with each other, about 5 of those are legacy “backbone” networks which have not been purchased by a broadband network. The rest are broadband networks guarding their monopoly positions. (Interestingly, broadband networks without monopoly positions to guard do not require contracts.)
The other many 1000s of networks do not require contracts to peer.
The premise above therefore devolves to: Since most of the traffic is to those networks, then most of the bits flow over contracted peerings.
Perhaps “most” can be argued, but obviously a significant portion of all peering bits flow over contracted sessions. Hopefully we can all agree on that.
And let’s also agree there are reasons to have contracts. Peering can require a great deal of time, effort, and money. Peering can require contracts with transport providers, equipment suppliers, colocation facilities, etc. I’m not saying everyone should have a contract for everything. I’m just saying there are good and valid reasons for them, at least sometimes.
But saying “most bits flow over contracts” is not the end of the story.
First, look at the three content “networks” with the most traffic - Google, Netflix, Akamai. All will peer without contracts. All peer at IXes. In fact, all are happy to exchange traffic without even an email to the other network (i.e. route-server peerings). Since these three networks are some of the largest (the largest?) on the planet, it is clear that volume alone does not create the requirement for a contract.
Also, let’s take the bottom 10K peering networks. They will not get peering with Comcast, DT, CT, Telstra, FT, etc. Meaning pretty much all their peering bits are over un-contracted sessions. The rest is transit.
I guess you could say the bits sent over transit will eventually hit a contracted peering session, since the people in the core contract their sessions. But does that matter to the small guys?
In summary, lots of bits flow over contracted peering sessions. But more sessions are not contracted. And lots of bits flow over those non-contracted sessions.
Going back to my original post, I was trying to show there are plenty of jobs for peering people who will rarely or even never sign a contract. Plus this is a great place to learn things like capacity planning, BGP, and other technologies required to do peering well. If you are good, you can learn the commercial underpinnings of peering.
Then if you are lucky enough to score a job with a legacy “tier one” which still thinks it is relevant, or a monopolistic broadband company, you can learn contracts after the fact.