Analog data - take on continuous values on some interval. Digital data - take one discrete values. Digital signal - discrete or discontinuous signal, such as a sequence of voltage pulses. Cheaper, less susceptible to noise, but suffers from attenuation. Analog and digital data can be propagated by either analog or digital signals.
Permits use ofmodern digital transmission and switching equipment.
Optical fiber and satellite only propagate analog signals. Analog transmission - means of transmitting analog signals without regard to their content. Signal may represent analog data or digital data. Attenuation is a problem, improved with amplifiers. Amplifiers cause noise, not a problem with voice, but bad for digital data.