GAO V.21 Channel 2 fax software implements channel two of the ITU-T V.21 Recommendation, which provides a 300 bits per second duplex modem standard for use in the general switched telephone network. The ITU-T V.21 Recommendation states that Frequency Shift Modulation should be used resulting in a modulation rate being equal to the data signaling rate. The nominal mean frequency for channel 2 is 1750 Hz. Channel 2 shall be used for transmission of check signals and service signals from the called station to the call-originating station, regardless of the direction in which the data are transmitted.
For information on Fax Relay, please see GAO's Fax Relay Software.