ntendre for "fiber-optic network" as well as "phone"), but that did not mean it was in any hurry to lease the fiber. ISPs Wanted Dark Fiber The Internet service providers were not like most telecommunications custom- ers. For one thing, their bandwidth requirements were simply not in the same league. For another, they were usually run by technologists who knew quite well how the telecommunications networks operated. They heard the hype about The Deuteronomy Networks fiber optics and bought in: They wanted fiber, not just fixed bit rate services. They wanted to be able to upgrade their networks rapidly, on their own: Even though their traffic was not really doubling every hundred days, it was growing rapidly. But it is not practical for many companies to lay their own dark fiber along the same rights-of-way. Most of the cost of fiber optics is in the installation, after all. Underground construction can cost $50,000 to $100,000 per mile. Aerial construction can cost about $10,000, if the poles are not too crowded, but poles can get crowded very quickly. It again has the characteristics of a natural monopoly. Carriers understand this. They often collaborate among themselves. Most undersea cables, for instance, are shared among many carriers. They own percentages of the cable, entitling each to a proportionate share of its capacity. Fiber-optic networks too are sometimes shared using a mechanism known as the indeasible right to use (IRU), typically for a certain number of strands along the route. A company purchases an IRU from the fiber's owner and gets total use of that fiber, typically for 20 years. The purchaser gets the dark fiber, and lights it however it sees fit. Traditional telephone carriers did not want to sell IRUs to potential cus- tomers, but ISPs did want to buy them. And some long distance companies, which owned their own switches, were interested in procuring IRUs for their backbone transmission, again an alternative to paying for, say, DS3 wholesale circuits. This provided an opportunity to compani