ephone network technology, including ISDN and future evolutionary technologies. It concludes with a qualitative evaluation of the advantages and disadvantages of ISDN-based Internet access. 3.1 Cable Technology Residential cable TV networks follow the tree and branch architecture. In each community, a head end is installed to receive satellite and traditional over-the-air broadcast television signals. These signals are then carried to subscriber's homes over coaxial cable that runs from the head end throughout the community Figure 3.1: Coaxial cable tree-and-branch topology To achieve geographical coverage of the community, the cables emanating from the head end are split (or "branched") into multiple cables. When the cable is physically split, a portion of the signal power is split off to send down the branch. The signal content, however, is not split: the same set of TV channels reach every subscriber in the community. The network thus follows a logical bus architecture. With this architecture, all channels reach every subscriber all the time, whether or not the subscriber's TV is on. Just as an ordinary television includes a tuner to select the over-the-air channel the viewer wishes to watch, the subscriber's cable equipment includes a tuner to select among all the channels received over the cable. 3.1.1. Technological evolution The development of fiber-optic transmission technology has led cable network developers to shift from the purely coaxial tree-and-branch architecture to an approach referred to as Hybrid Fiber and Coax(HFC) networks. Transmission over fiber-optic cable has two main advantages over coaxial cable: A wider range of frequencies can be sent over the fiber, increasing the bandwidth available for transmission; Signals can be transmitted greater distances without amplification. The main disadvantage of fiber is that the optical components required to send and receive data over it are expensive. Because lasers are s...
