till too expensive to deploy to each subscriber, network developers have adopted an intermediate Fiber to the Neighborhood (FTTN)approach. Figure 3.3: Fiber to the Neighborhood (FTTN) architecture Various locations along the existing cable are selected as sites for neighborhood nodes. One or more fiber-optic cables are then run from the head end to each neighborhood node. At the head end, the signal is converted from electrical to optical form and transmitted via laser over the fiber. At the neighborhood node, the signal is received via laser, converted back from optical to electronic form, and transmitted to the subscriber over the neighborhood's coaxial tree and branch network. FTTN has proved to be an appealing architecture for telephone companies as well as cable operators. Not only Continental Cablevision and Time Warner, but also Pacific Bell and Southern New England Telephone have announced plans to build FTTN networks. Fiber to the neighborhood is one stage in a longer-range evolution of the cable plant. These longer-term changes are not necessary to provide Internet service today, but they might affect aspects of how Internet service is provided in the future. 3.2 ISDN Technology Unlike cable TV networks, which were built to provide only local redistribution of television programming, telephone networks provide switched, global connectivity: any telephone subscriber can call any other telephone subscriber anywhere else in the world. A call placed from a home travels first to the closest telephone company Central Office (CO) switch. The CO switch routes the call to the destination subscriber, who may be served by the same CO switch, another CO switch in the same local area, or a CO switch reached through a long- distance network. Figure 4.1: The telephone network The portion of the telephone network that connects the subscriber to the closest CO switch is referred to as the local loop. Since all calls enter and exit the network ...
