Copyright Goodheart-Willcox Co., Inc. 81 Chapter 2 Network Media—Copper-Core Cable Summary Network Media ■ Th e three major classifi cations of network media are copper cable, fi ber-op- tic cable, and wireless radio waves. Analog and Digital Signals ■ Electronic signals are classifi ed as analog and digital. Analog and digital signals diff er by the shape of their waveforms. ■ In the analog signal, time aff ects the degree of the slope. In the digital signal, time aff ects the duration of the voltage level. ■ Both analog and digital waves have a frequency measurement. ■ Bandwidth is a measurement of the ability of network media to carry data, whereas frequency is a measurement of the ability of network media to carry an electronic signal. Data Transmission ■ Baseband is a method of transmitting a single frequency using the entire bandwidth of a cable. Broadband is a method of transmitting multiple frequencies or data across a cable at once. ■ Communication can occur in one of three modes: simplex, half-duplex, and full-duplex. Simplex communication occurs in one direction only. Half- duplex communication occurs in both directions, but not at the same time. Full-duplex communication occurs in both directions at the same time. Electronic Terms ■ Electrical energy that travels in only one direction is referred to as direct current (DC). ■ Electrical energy that constantly reverses its direction of fl ow is referred to as alternating current (AC). ■ Electrical resistance is the opposition to the fl ow of electrical energy. Resis- tance is generally used to describe this eff ect in DC circuits. ■ Impedance is also the opposition to the fl ow of electrical energy, but it ex- presses the amount of resistance encountered in an AC circuit. ■ Refl ected loss is the amount of signal refl ected from the far end, or receiving end, of a cable. ■ Th e electrical phenomenon of a current-carrying conductor inducing cur- rent in a cable of close proximity is called crosstalk. ■ Near-End Crosstalk is a measurement of crosstalk at the near end, or send- ing end, of a cable. ■ Alien Crosstalk is crosstalk generated from network cables in close proximity to each other. ■ Th e decibel (dB) is an electrical measurement that is used to express the amount of power or energy gained or lost. ■ Far-End Crosstalk is a measurement of crosstalk at the far end, or receiving end, of a cable.