er coax (HFC) architectures, support 750MHz or 1,000MHz systems. (HFC is discussed in detail in Chapter 12.) Therefore, coax provides from 370 to 1,000 times more capacity than single twisted-pair. With this additional capacity, you can carve out individual channels, which makes coax a broadband facility. Multiplexing techniques can be applied to coax to derive multi- ple channels. Coax offers slightly better performance than twisted-pair because the metallic shielding protects the center conductor from outside interferences; hence the performance of coax is on the order of 10-9 (i.e., 1 in 1 billion) bps received in error. Amplifiers need to be spaced every 1.5 miles (2.5 km) which is another improvement over twisted-pair, but it still means a substantial number of amplifi- ers must be deployed throughout the network. Cable TV operators, like the telephony network providers, have been prevalent users of coax, but in the past decade, they have been reengineering their backbone networks SO that they are fiber based, thereby eliminating many amplifiers and subsequently improving performance. Remember from Chapter 1, "Telecommuni- cations Technology Fundamentals," that amplifiers accumulate noise over a dis- tance. In a large franchise area for a cable TV operator, toward the outer fringes, greater noise accumulates and a lower service level is provided there than to some of the users upstream. By reengineering their backbones to be fiber based, cable providers can also limit how many amplifiers have to be deployed, along with reap- ing other advantages, such as high bandwidth, immunity to electrical interference, and improved security. One problem with coax has to do with the deployment architecture. Coaxial cable and HFC architectures are deployed in bus topologies. In a bus topology, the Coaxial Cable bandwidth is shared, which means congestion levels increase as more users in the neighborhood avail themselves of these features and services. A bus topology also presents security risks. It's sort of like going bac