Electronic device that converts digital data into analog (modulated-wave) signals suitable for transmission over analog telecommunications circuits (e.g., traditional phone lines) and demodulates received analog signals to recover the digital data transmitted.
The "modulator/demodulator" thus makes it possible for existing communications channels to support a variety of digital communications, including e-mail , Internet access, and fax transmissions. An ordinary modem, operating over traditional phone lines, has a data transmission speed limit of about 56 kilobits per second. ISDN lines allow communications at over twice that rate, and cable modem s and DSL lines have transmission rates of over a million bits per second.