US Robotics COURIER - HST (High Speed Technology)

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COURIER HIGH SPEED MODEMS
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.
HDLC
HST
Hz
High Level Data Link Control. A standard protocol developed
by the International Standards Organization for software appli-
cations and communicating devices operating in synchronous
environments. The protocol defines operations at the link level
of communications, for example, the format of data frames
exchanged between modems over a phone line. See Bisync,
Protocol, SDLC.
High Speed Technology, USRobotics' proprietary signaling
scheme, design and error control protocol for high-speed
modems. HST incorporates trellis-coded modulation, for greater
immunity from variable phone line conditions, and asym-
metrical modulation for more efficient use of the phone channel
at speeds of 4800 bps and above. HST also incorporates MNP-
compatible error control procedures adapted to asymmetrical
modulation.
Hertz, a frequency measurement unit used internationally to
indicate one cycle per second.
LAPM
Link Access Procedure for Modems, an error control protocol
incorporated in CCITT Recommendation V.42. Like the MNP
and HST 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 send copies of key-
board commands and transmitted data to the screen. When the
modem is in Command mode (not online to another system) the
local echo is invoked through the ATEl command. The com-
mand causes the modem to display your typed commands.
Glossary G-7