cost-effective solution, despite performance problems due to weather issues. Twisted-pair will see little use with the future application set. Although there have been some vast improvements in carrying high bit rates over very-short-distance twisted-pair, such as VDSL (covered in Chapter 12, "Broad- band Access Alternatives"), this is not a long-term solution; it is simply a way to extend the useful life of an embedded base of copper. This is why you don't see any new housing developments being wired with copper; instead, telcos and even developers are engaged in bringing fiber to and into the home. And of course, wire- less will also figure prominently in enabling mobility. Figure 1.8 plots various tele- communications devices on the electromagnetic spectrum. Bandwidth As mentioned earlier, bandwidth is the range of frequencies that make up a signal. (Note that the term is today commonly used to refer to data rate, even though that is not the technically correct definition.) There are three major classes of band- width in telecommunications networks: narrowband, wideband, and broadband. Narrowband Narrowband can accommodate up to 64Kbps, which is also known as the DS-0 (Digital Signal level 0) channel. This is the fundamental increment on which digi- tal networks were built. Initially, this metric of 64Kbps was derived based on our understanding of what it would take to carry voice in a digital manner through the network. If we combine these 64Kbps channels, we can achieve wideband trans- mission rates. Wideband Wideband is defined as accommodating n X 64Kbps, up to approximately 45Mbps. A range of services are provisioned to support wideband capabilities, including T-carrier, E-carrier, and J-carrier services. These are the services on which the first generation of digital hierarchy was built. Chapter 1 Telecommunications Technology Fundamentals X-rays, Microwave Radio Coaxial FM/TV Terrestrial Broadcast Microwave Satellites AM Radio Telephone Cellular Shortwave Telephone Figure 1.8 Telecommunications devices 