Glossary
Glossary-5
3825-A2-GB30-20
November 1996
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 that glows in response to the
presence of a certain condition (e.g., Alrm).
local analog loopback
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
A telephone or modem is being used.
on-hook
A telephone or modem is not being used.
Originate mode
The modem is in a state where it is ready to transmit a call. In a dial network, it is the modem that
makes the call. In a leased-line network, it is one of two sides of the network that is selected to be
the originating modem.
parity
A way of checking data accuracy by counting the number of bits that have a value of one.
PBX
Telephone switching equipment (Private Branch Exchange) dedicated to one customer. A PBX
connects private telephones to each other and to the public dial network.
permissive interface
A dial modem operating mode characterized by a fixed output power level of –9 dBm. It is one of
two possible modes of operation for modems connected to dial lines (see programmable
interface).
power-up self-test
A test that checks most hardware components when the modem is powered-on.
product code
A three-digit code indicating the modem’s highest VF data rate.
programmable interface
A dial modem operating mode characterized by an output power level (–12 to 0 dBm) set by a
programming resistor in the jack. It is one of two possible modes of operation for modems
connected to dial lines (see permissive interface).
protocol
The rules for timing, format, error control, and flow control during data transmission.
PSTN
Public Switched Telephone Network. A network shared among many users who can use
telephones to establish connections between two points. Also known as dial network.
pulse dialing
One of two dialing methods, in which telephone numbers are sent as pulses (brief changes in
voltage or current intensity) across the telephone line. Rotary telephones use pulse dialing.
