 was based on the one-way broadcast of programming to subscribers. It is well known that the ability to use a cable modem requires a bidirec- tional transmission capability. This means that the original CATV net- work infrastructure based on the use of unidirectional amplifiers was Fiber in the Neighborhood Figure 7.6 The initial cable TV network infrastruc- ture was based on Cable TV the use of one-way Headend amplifiers. Legend: S subscriber Unidirectional coaxial amplifier incapable of supporting the use of cable modems. As an interim mea- sure, some CATV operators initially marketed cable modems that used the public switched telephone network (PSTN) for uplink communica- tions, while downlink communications occurred via the coaxial-cable infrastructure. Because this represents an interim solution as CATV operators invest billions of dollars in upgrading their infrastructure to support bidirectional data services, we will focus on the use of bidirec- tional transmission over the CATV infrastructure in the remainder of this chapter. Now that we have a general idea of how the original CATV network infrastructure was designed, let's focus on the evolving telephone and CATV network infrastructure In SO doing, we will note the routing of fiber to the neighborhood, including the practicality of fiber to the curb and fiber to the home. The Evolving Local Telephone Network In this section we will examine the evolving local telephone network. Here the key term to note is "local," since the use of fiber in the back- bone of long-distance communications carriers commenced during the Chapter Seven 1970s. In comparison, the use of fiber in the local telephone network is a fairly recent phenomenon, since it is more expensive to replace cable in urban areas than place fiber on the railroad and pipeline rights-of-way commonly used to link cities together. Overview The ability to support broadband communication in the local telephone company depends on the type of cabling used to link subscribers to a central office and the di