Modem

A device that converts digital data into signals suited to a communication channel and converts received signals back into digital data.

Modulation: The process of varying a signal’s properties to encode information for transmission. A modem’s transmitter encodes data by changing a carrier signal’s properties.
Acoustic coupler: A device that connects a computer to a telephone line through a telephone handset’s speaker and microphone. Early computer modems often sent their audio signals through acoustic couplers.
Digital signal: A signal that represents information using a discrete set of values. Modems begin with digital data that must be represented on a physical channel.
Cable modem: A device that provides internet access over a cable television network. It uses cable-network channels to carry broadband data between homes and providers.
Router: A network device that forwards packets between different networks. A router directs traffic among networks; it does not itself adapt signals to an access channel.
Demodulation: The recovery of information from a modulated signal. A modem’s receiver extracts transmitted data from the incoming signal.
Bell 103 modem: A 300-bit-per-second telephone modem standard introduced by AT&T in 1962. Its frequency-shift signaling became an early model for dial-up computer communication.
Analog signal: A continuously varying signal that can represent information through changes in amplitude, frequency, or phase. Traditional telephone modems translated digital data into signals carried by analog voice circuits.
DSL modem: A device that connects to internet service over a digital subscriber line. It adapts data to high-frequency signals on copper telephone wiring.
Network interface controller: Hardware that connects a computer to a network and handles link-level communication. A network interface connects local devices, while a modem bridges data to an access-line signal.

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