G
LOSSARY
7-5
online fall back/fall forward
A feature that allows high-speed, error-control modems to monitor line
quality and fall back to the next lower speed in a defined range if line
quality diminishes. As line conditions improve, the modems switch up to
the next higher speed.
originate mode
The mode used by your modem when initiating an outgoing call to a
destination modem. The transmit/receive frequencies are the reverse of the
called modem, which is in
answer mode
.
parity
A simple error-detection method that checks the validity of a transmitted
character
. Character checking has been surpassed by more reliable and
efficient forms of error checking, including
V.42
and
MNP 2-4 protocols
.
Either the same type of
parity
must be used by two communicating
computers, or both may omit parity.
protocol
A system of rules and procedures governing communications between two
or more devices. Protocols vary, but communicating devices must follow
the same protocol in order to exchange data. The format of the data,
readiness to receive or send, error detection and error correction are some
of the operations that may be defined in protocols.
RAM
Random Access Memory. Memory that is available for use when the
modem is turned on, but that clears of all information when the power is
turned off. The modem's RAM holds the current operational settings, a
flow control
buffer
, and a command
buffer
.
remote digital loopback
A test that checks the phone link and a remote modem's transmitter and
receiver.
remote echo
A copy of the data received by the remote system, returned to the sending
system, and displayed on the screen. Remote echoing is a function of the
remote system.
ROM
Read Only Memory. Permanent memory, not user-programmable.
serial transmission
The consecutive flow of data in a single channel. Compare to parallel
transmissions where data flows simultaneously in multiple channels.
start/stop bits
The signaling bits attached to a
character
before and after the character is
transmitted during
asynchronous transmission
.
terminal
A device whose keyboard and display are used for sending and receiving
data over a communications link. Differs from a microcomputer or a
mainframe in that it has little or no internal processing capabilities.
terminal mode
Software mode that allows direct communication with the modem. Also
known as command mode.
throughput
The amount of actual user data transmitted per second without the
overhead of
protocol
information such as
start/stop bits
or
frame
headers
and trailers. Compare with
characters per second
.
V.8
The
ITU-T
standard specification that covers the initial handshaking
process.
V.17 fax
An
ITU-T
standard for making
facsimile
connections at 14,400 bps,
12,000 bps, 9600 bps, and 7200 bps.
V.21
An
ITU-T
standard for modems operating in asynchronous mode at speeds
up to 300 bps,
full-duplex
, on public switched telephone networks.
V.22
An
ITU-T
standard for modem communications at 1200 bps, compatible
with the Bell 212A standard observed in the U.S. and Canada.
Summary of Contents for 3CP5613
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