Comcast digital transport remote?

How much does it cost a US ISP, e.g. Comcast, to transport 1GB of data across its network versus across N interconnects?

• E.g. how much would it cost Comcast to deliver 1GB from a Comcast-connected server to a Comcast-connected user versus from an AT&T-connected server to a Comcast-connected user?

• Answer:

  For big providers like Comcast and AT&T, the answer is probably nothing, as they should have a direct peering agreement. Understand that this makes sense for two reasons: First, traffic in the Internet is always bidirectional. Packets come and packets go. More important, someone is paying to have this content hosted at AT&T, and this customer is paying not only for the physical hosting of the server, but more important, he wants that everyone in the Internet should be able reach that server. If AT&T doesn't make this guarantee (that the content will be made available to everyone) then he'll probably host the server somewhere else. So AT&T is already paid to transport that data inside it's network. If Comcast and AT&T didn't make a direct peering agreement, then both companies end up having to pay someone else (a third party) to make this connection, and both will be charged for transit. That's wh it doesn't make any sense. Smaller providers don't have either the clout, or the technical capacity, to peer with everyone, so they end up buying transit from some company. Then the answer depends on the cost of transit, which varies a lot from coutry to country. As a last note, traffic between ISPs isn't measured in volume (MB or GB) but in throughput (Mbps or Gbps). CDNs, however, charge for volume transferred, but that's another business model.