Digital Modem - A modem that accepts an analog call over a 64 kilobit (or higher) ISDN channel and interprets it via software as a call originated by an analog modem. This process often requires the use of a digital signal processor (DSP) to break the analog signal into an equivalent digital bit stream.  (2003 definition.) http://en.wikipedia.org/wiki/Modem.

See the Interactive Television Institute.