lly, you need to consider three types of costs associated with the media types: acquisition cost (e.g., the costs of the cable per foot [meter], of the trans- ceiver and laser diode, and of the microwave tower), installation and maintenance costs (e.g., the costs of parts as a result of wear and tear and environmental condi- tions), and internal premises costs for enterprises (e.g., the costs of moves, adds, and changes, and of relocating workers as they change office spaces). The following sections examine these five media types-twisted-pair, coaxial cable, microwave, satellite, and fiber optics-in detail. Twisted-Pair The historical foundation of the public switched telephone network (PSTN) lies twisted-pair, and even today, most people who have access to networks access them through a local loop built on twisted-pair. Although twisted-pair has contributed a great deal to the evolution of communications, advanced applications on the hori- zon require larger amounts of bandwidth than twisted-pair can deliver, SO the future of twisted-pair is diminishing. Figure 2.1 shows an example of four-pair UTP. Characteristics of Twisted-Pair The total usable frequency spectrum of telephony twisted-pair copper cable is about 1MHz (i.e., 1 million cycles per second). Newer standards for broadband DSL, also based on twisted-pair, use up to 2.2MHz of spectrum. Loosely translated into bits per second (bps)-a measurement of the amount of data being trans- ported, or capacity of the channel-twisted-pair cable offers about 2Mbps to 3Mbps over 1MHz of spectrum. But there's an inverse relationship between dis- tance and the data rate that can be realized. The longer the distance, the greater the impact of errors and impairments, which diminish the data rate. In order to achieve higher data rates, two techniques are commonly used: The distance of the loop can be shortened, and advanced modulation schemes can be applied, which Twisted-Pair Figure 2.1 Twisted-pair means we can encode more bits per cycle. A good example of this is Short