G
LOSSARY
7-4
facsimile
A method for transmitting the image on a page from one point to another.
Commonly referred to as fax.
fax mode
The mode used by a modem to send and receive data in
facsimile
format.
See definitions for
V.17, V.27ter, V.29
.
flow control
A mechanism that compensates for differences in the flow of data into and
out of a modem or other device. See commands &Hn, &In, &Rn.
frame
A
data communications
term for a block of data with header and trailer
information attached. The added information usually includes a frame
number, block size data, error-check codes, and Start/End indicators.
full duplex
Signals can flow in both directions at the same time over one line. In
microcomputer communications, this may refer to the suppression of the
online
local echo
.
half duplex
Signals can 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 cycles
per second.
Internet
An electronic communications network that connects computer networks
and organizational computer facilities around the world.
Internet Service Provider
A company which provides dial-up (modem) access to the
Internet
for a
fee.
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
.
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 En.
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 flawed
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.
nonvolatile memory (NVRAM)
User-programmable random access memory whose data is retained when
power is turned off. On the U.S. Robotics modem, it includes four stored
phone numbers and the modem settings.
off/on hook
Modem operations that are the equivalent of manually lifting a phone
receiver (taking it off-hook) and replacing it (going on-hook).
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