ine, a telephone company can deliver a high-speed access service on the same line that delivers standard telephony. Unfortunately, DSL is severely limited by the quality and length of the copper loop. DSL connections can be restricted or even made unworkable if the copper loop has been modified with loading coils, which improve voice transmission on longer loops. More important, the ability of copper The Broadband Revolution telephone loops to carry high-speed data signals declines with distance. ADSL permits downstream speeds of up to 8 megabits a second and upstream speeds of up to 640 kilobits a second, but speeds are much lower over the average loop. In fact, most U.S. ADSL subscribers realize down- stream speeds of less than 1 megabit a second. ADSL modems do not oper- ate reliably over copper loops longer than approximately three miles, a sig- nificant constraint in a country with a dispersed population. In order to offer DSL service, a telephone company must install a DSL modem at the customer premises and at the central office or the remote ter- minal. Usually the modems in central offices come in assemblies of multi- ple modems called digital subscriber line access multiplexers (DSLAMs). The DSLAM must then have a high-speed connection to the rest of the Internet. To improve the quality of all telephone services and to be able to offer DSL services in areas of low to moderate population density, telephone companies have extended fiber optics to remote terminals, where the light waves are converted to electrical signals and transmitted to the subscriber over much shorter copper lines. This architecture is known as digital loop carrier (DLC) and requires substantial investment in fiber optics and elec- tronics at the remote terminals. In recent years, the incumbent telephone companies have been deploying this technology SO as to offer DSL to more subscribers, but this deployment has arguably been delayed somewhat by uncertainty over whether the incumbent companies must share these facil- ities with new ent