Companies. All rights reserved. Any use is subject to the Terms of Use as given at the website. First Things First First Things First Figure 1-11 Subscriber 1: 0-4,000 Hz Frequency- division multiplexing Subscriber 2: 4,000-8,000 Hz (FDM) Subscriber 3: 8,000-12,000 Hz Subscriber 4: 12,000-16,000 Hz Subscriber 5: 16,000-0,000 Hz Analog versus Digital Signaling: Dispensing with Myths FDM is normally considered to be an analog technology, while time-divi- sion multiplexing is a digital technology. The word "analog" means "something that bears a similarity to something else," while the word "digital" means "discrete." Analog data, for example, typically illustrated as some form of sine wave such as that shown in Figure 1-12, is an exact representation of the values of the data being transmitted. The process of using manipulable characteristics of a signal to represent data is called signaling. Figure 1-12 Sine wave Downloaded from Digital Engineering Library @ McGraw-Hill (www.digitalengineeringlibrary.com Copyright © 2004 The McGraw-Hill Companies. All rights reserved. Any use is subject to the Terms of Use as given at the website. First Things First Chapter 1 We should also introduce a few terms here just to keep things mar- ginally confusing. When speaking of signaling, the proper term for digi- tal is baseband, while the term for analog signaling is broadband. When talking about data (not signaling), the term "broadband" means "big channel." The sine wave, undulating along in real time in response to changes in one or more parameters that control its shape, represents the exact value of each of those parameters at any point in time. The parameters are amplitude, frequency, and phase. We will discuss each in turn. Before we do, though, let's relate analog waves to the geometry of a cir- cle. Trust me-this helps. Consider the diagram shown in Figure 1-13. As the circle rolls along the flat surface, the dot will trace the shape shown by the dotted line. This shape is called a sine wave. If we examine this waveform c