th 10 or more telephone number prefixes. However, the basic structure of the local loop has not changed. Connection Methods Because of economics, the local loop originating from a subscriber may not directly flow on an individual twisted pair to a telephone company central office. Instead, subscriber lines are typically routed to a neighborhood location where a number of subscriber lines are either bundled together for routing to the serving telephone company cen- tral office or are multiplexed to that office. THE FEEDER DISTRIBUTION INTERFACE Bundling that occurs at the location where individual wire pairs are grouped together is referred to as a feeder distribution interface (FDI). At the FDI, up to 1000 and possibly more individual twisted-pair wires are bundled and routed to a central office. The top portion of Figure 7.2 illustrates the use of an FDI to interconnect a grouping of residential and business subscribers located within a neighborhood to a telephone company central office. In examining the top portion of Figure 7.2, note that through the use of a bundle of copper pairs routed from the FDI to the central office, only one right-of-way is required. In addition, because a common path is used between the FDI and the central office, it is easier and less costly to route the bundled copper. Fiber in the Neighborhood Home/ Figure 7.2 Office Local loop connec- tion options. twisted copper bundle Home/ Central Office Office T1/E1 Home/ Office twisted Home/ Legend: Office FDI Feeder Distribution Interface DLC Digital Loop Carrier RT Remote Terminal THE DIGITAL LOOP CARRIER REMOTE TERMINAL A second method commonly used to connect a large number of subscribers to a central office involves the use of a copper-based T1 or E1 transmission lines. In this method subscriber lines are first routed to a digital loop car- rier (DLC), which represents an intermediate location between a group of subscribers and the central office. In telephone company terminology, these intermediate locations are referred to as remote te