ders, that are designed to improve the quality of voice calls. Unfortunately, these devices also interfere with the provision of DSL service. Thus, before loops can be used for DSL, they must be "conditioned" by removing all of these devices. In addition, for a single telephone line to be used to carry both voice and data traffic, the network owner must install equipment in its central office to separate voice traffic from data traffic. This typically involves the installation of a device known as a digital subscriber line access multiplexer (DSLAM). The relevant loops are connected to the DSLAM, which routes voice communications into a conventional circuit-switched network and routes data communications into a packet-switched network. The fact that resistance increases with the length of the copper wire places a natural limit on the range of DSL. For asymmetric DSL, which is the most commonly deployed DSL technology, customers must be located no farther than twelve to eighteen thousand feet from the DSLAM. For faster DSL technologies, such as very high- data-rate digital subscriber line (VDSL), customers must be located no more than four thousand feet from the DSLAM (see Figure 10.2). This scenario changes somewhat in situations in which a local telephone com- pany has deployed a technology known as digital loop carriers (DLCs). Instead of using an all-copper loop to transmit analog signals between the central office and the customer's premises, DLC systems use fiber optics to establish a digital connection between the central office and a satellite facility known as a remote ter- minal, where the transmission is converted into an analog format and distributed to the customer's premises through a copper subloop.1 The improved efficiency and 16 See, e.g., Kiser and Collins (2003); Nakahata (2002). 17 For simplicity, Figure 10.3 omits the fact that remote terminals are actually deployed in a ring configuration. Networks in Telecommunications Central Office Customer DSLAM Premises Circuit Voice Conditioned Voice Sw