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Glossary
Glossary-53821-A2-GB20-30 February 1998
handshaking The exchange of predetermined codes and signals (tones) to establish a connection
between two modems.
HDLC High-level Data Link Control. A communications protocol defined by ISO.
host A computer attached to a network that shares its information and devices with the rest of
the network.
Hz A unit of frequency (hertz) that equals one cycle per second.
ISO International Organization for Standardization.
ITU-T The Telecommunications Standardization Sector of the International
Telecommunications Union, an advisory committee established by the United Nations to
recommend communications standards and policies. Before March 1993 it was called
CCITT.
JM8 A jack used for leased-line networks. Pins 1 and 2 are the transmit pair and Pins 7 and 8
are the receive pair.
LCD Liquid Crystal Display. The device that permits text to be displayed on the DCP or
SDCP.
leased line A private line connection exclusively for the user. No dialing is necessary.
LED Light-Emitting Diode. A light or status indicator on the DCP or SDCP that glows in
response to the presence of a certain condition (e.g., Alrm).
local analog loopback Test in which the modem’s transmit VF signal is looped to its receiver.
long space disconnect A disconnect can occur if the modem receives an extended space from a remote modem;
for example, when a remote modem is commanded to disconnect, it transmits a
continuous space to the modem before disconnecting.
loopback test Any test that verifies a device’s integrity by connecting the device’s output of one
direction to the device’s input of the other direction, then checking the received signal
for errors.
LSD Line Signal Detect. A signal between the DTE and modem indicating energy exists on
the transmission circuit.
MNP This protocol (Microcom Networking Protocol) detects and corrects data errors caused
by telephone line noise and signal distortion. MNP5 includes data compression.
modem MOdulator/DEModulator. A device that transforms signals from digital to analog form
and vice versa.
modulation The process of varying some characteristics (usually amplitude, frequency, and/or phase)
of a carrier wave to form data transmissions.
off-hook The state of a telephone or modem that is being used.
on-hook The state of a telephone or modem that is not being used.