What is the difference between a data modem and a fax modem?
Data modems and fax modems are different in modulation methods (tones) used to communicate data. Typically the modulation schemes used for fax are synchronous half-duplex while those used for data (at least by most UNIX and PC people) are asynchronous and full-duplex. Also, data modems, once they have negotiated a modulation scheme, tend to continue with the same one through out the session. Fax modems switch before and after each page between a high-speed modulation scheme used to transmit the image data and a lower (300 or 2400 bps) scheme to exchange control information.
