k to the party line in telephony. You do not have your own dedicated twisted-pair that's yours and only yours. Instead, several channels devoted to voice telephony are shared by everyone in the neigh- borhood, which makes encryption important. Also, there are some problems with noise in bus topologies. The points where the coax connects into set-top boxes or cable-ready TV sets tend to collect noise, so the cable tends to pick up extraneous noise from vacuum cleaners or hair dryers or passing motorcycles. Thus, if every household on the network is running a hair dryer at 6:30 AM, the upstream paths are subjected to this noise, resulting in some performance degradation. (Bus topol- logies are discussed in more detail in Chapter 6, "Local Area Networking.") Applications of Coaxial Cable In the mid-1920s, coax was applied to telephony networks as interoffice trunks. Rather than having to add more copper cable bundles with 1,500 or 3,000 pairs of copper wires in them, it was possible to replace those big cables (which are very difficult to install cost-effectively) with a much smaller coaxial cable. The next major use of coax in telecommunications occurred in the 1950s, when it was deployed as submarine cable to carry international traffic. It was introduced into the data-processing realm in the mid- to late 1960s. Early com- puter architectures required coax as the media type from the terminal to the host. LANs were predominantly based on coax from 1980 to about 1987. Coax has been used in cable TV and in the local loop, in the form of HFC archi- tectures. HFC brings fiber as close as possible to the neighborhood; then on a neigh- borhood node, it terminates that fiber, and from that node it fans the coax out to the home service by that particular node. (This is described in detail in Chapter 12.) Advantages and Disadvantages of Coaxial Cable The advantages of coax include the following: Broadband system-Coax has a sufficient frequency range to support mul- tiple channels, which allows for much greater throughput. G