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. Digital transmission - concerned with content of the signal. Repeaters are used to avoid attenuation over distances.
Digital transmission is considered superior to analog.
Minimize errors in determining start and end of each bit and errors in determining whether each bit is a 1 or a 0. Analog data - encoding scheme is designed to enhance quality of transmission. Digital info is encoded by means of a modem that modulates one of the threecharacteristics of the carrier - amplitude, frequency, or phase. Used to transmit digital data over optical fiber. Less susceptible to error than amplitude-shift keying.