her than being a continuously variable waveform, it is a series of discrete pulses, representing one bits and zero bits (see Figure 1.10). Each computer uses a coding scheme (called a collating sequence) that defines what com- binations of ones and zeros constitute all the characters in a character set (e.g., lowercase letters, uppercase letters, punctuation marks, digits, keyboard control functions). How the ones and zeros are physically carried through the network depends on whether the network is electrical or optical. In electrical networks, one bits are represented as high voltage, and zero bits are represented as null, or low voltage. In Chapter 1 Telecommunications Technology Fundamentals Binary Digits Figure 1.10 Digital transmission optical networks, one bits are represented by the presence of light, and zero bits are represented by the absence of light. The ones and zeros-the on/off conditions- are carried through the network, and the receiving device repackages the ones and zeros to determine what character is being represented. Because a digital signal is easier to reproduce than an analog signal, we can treat it with a little less care in the network. Rather than use dumb amplifiers, digi- tal networks use regenerative repeaters, also referred to as signal regenerators. As a strong, clean, digital pulse travels over a distance, it loses power, similar to an ana- log signal. The digital pulse, like an analog signal, is eroded by impairments in the network. But the weakened and impaired signal enters the regenerative repeater, where the repeater examines the signal to determine what was supposed to be a one and what was supposed to be a zero. The repeater regenerates a new signal to pass on to the next point in the network, in essence eliminating noise and thus vastly improving the error rate. Analog Versus Digital Transmission Table 1.1 summarizes the characteristics of analog and digital networks. Conversion: Codecs and Modems Today we don't have all-digital or all-analog networks; we have a mix of t