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retrain. An adjustment process performed when one of the modems detects signal distortion or
line noise which threaten data integrity.
RTS/CTS. Request to Send/Clear to Send. RTS and CTS are two control signal lines between the
modem (DCE) and terminal (DTE) which allow the terminal to control the flow of information.
See also flow control.
S
sleep inactivity timer. Determines the length of time the modem operates in normal mode with
no activity before entering low-power “sleep” mode.
split-speed direction. Determines which direction (transmit or receive) has the 75bps channel
and which has the 1200bps channel.
standard AT-command. The basic AT command set, originated by Hayes Microcomputer
Products, Inc.
synchronous communications. A method of transmission in which data bits are sent
continuously at the same rate under the control of a fixed frequency clock signal.
T
touch-tone dialing. Push-button tone dialing as used on contemporary phone sets. The dial
modifier ATDT sets the modem to “tone” mode. Tone dialing is faster and more reliable than
older-style pulse dialing.
trellis coding. A method of modulation which targets specific modulation points. Signals falling
outside of these points are treated as line noise, thus ensuring greater noise immunity over a
given line. QAM (Quadrature Amplitude Modulation) functions similarly, but has a broader
tolerance and results in lesser noise immunity than trellis coding.
X
XON/XOFF. XON and XOFF are the names of two different flow control characters. See also
flow control.
Acknowledgments
The Complete Modem Reference. Gilbert Held. John Wiley & Sons, Inc.
Upgrading and Repairing PCs. (Second Edition). Que Corporation.
Glossary of Modem Communication Terms
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