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Half Duplex
Signal flow in both directions, but only one way at a time. In microcomputer communications, may refer to activation
of the online Local Echo, which causes the modem to send a copy of the transmitted data to the screen of the
sending computer.
Hz
Hertz, a frequency measurement unit used internationally to indicate one cycle per second.
ITU-T
An international organization that defines standards for telegraphic and telephone equipment. For example, the Bell
212A standard for 1200-bps communication in North America is observed internationally as ITU-T V.22. For 2400-
bps communication, most U.S. manufacturers observe V.22 bis. The initials ITU-T represent the French name; in
English it's known as the International Telegraph and Telephone Consultative Committee.
LAPM
Link Access Procedure for Modems, an error-control protocol defined in ITU-T Recommendation V.42. Like the
MNP protocols, LAPM uses cyclic redundancy checking (CRC) and retransmission of corrupted data (ARQ) to
ensure data reliability.
Local Echo
A modem feature that enables the modem to display keyboard commands and transmitted data on the screen. See
command Hn.
MNP
Microcom Networking Protocol, an error-control protocol developed by Microcom, Inc., and now in the public
domain. There are several different MNP protocols, but the most commonly used one ensures error-free
transmission through error detection (CRC) and retransmission of errored frames.
Modem
A device that transmits/receives computer data through a communications channel such as radio or telephone
lines. It also changes signals received from the phone line back to digital signals before passing them to the
receiving computer.
