0049-1800-xxx 326X V.34, V.34-SDC and V.32bis Series Modem – USER’S GUIDE 02/23/2010
Rev. A
Page 203
of
205
Leased Line
A dedicated telephone-line circuit permanently connecting two or more locations
and used solely by one customer, who leases the line.
LED
Light Emitting Diode.
Loopback
(1) A method of feeding a received signal back from a point in a data link to the
receiver at the site where the data was originated. Commonly used to test
portions of a data link to isolate faulty equipment or data lines. (2) The feeding
back of data from a point in a data path to the transmitting source for testing. (3)
A diagnostic procedure that sends a test message back to the originator, which
compares the message with the original transmission. Loopback testing can occur
within a locally attached device or can be conducted remotely over a
communications circuit.
LPDA2
Feature that enables the 326X to be used in an IBM dial and leased line restoral
applications using LPDA2 Dial and Disconnect commands.
Modem
Modulator/demodulator, enabling digital data to be sent over analog transmission
facilities.
Modulation
Systematic changing of properties (e.g., amplitude, frequency, phase) of an analog
signal to encode and convey digital information.
MNP
Microcom Networking Protocol. An asynchronous communications protocol that
provides error correction.
Multiplexer
(1) Any multiport device that allows two or more users to share a common
physical transmission channel; employed in pairs, one at each end of the channel,
where each device performs both multiplexing of the multiple user inputs and
demultiplexing of the channel back into the separate user data streams. (2) A
device that allows two or more analog data signals to be transmitted
simultaneously over a single telephone line.
Off-hook
The description for when a telephone or modem connects to the dial line and
presents electrical characteristics, similar to when a telephone handset is removed
from the cradle.
Parity bit
An error-checking mechanism for asynchronous transmission. An additional
nondata bit added to a group of bits, that indicates whether the number of “1”s in
the group is odd or even.
PBX
Private branch exchange. A telephone switching system located on a customer’s