All tier 1 ISPs have peering agreements where most pay nothing for traffic transfer. The real costs are the equipment, ISPs use statistical multiplexing to maxi

All tier 1 ISPs have peering agreements where most pay nothing for traffic transfer. The real costs are the equipment, ISPs use statistical multiplexing to maximize the value of their lines and switches. Data caps only affect this indirectly, it is bandwidth that matters. If an ISPs' equipment can only handle 10Gb/s of bandwidth without degrading that is the real limit, the total amount of data a month is mostly immaterial. Simply put if everyone used up their data cap on the first day of the month the ISP could not handle it even though no one went over their cap.