Boca SoundExpression 14.4VSP, User Manual, Page: 64 / 96

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SoundExpression
dial modifier . Dial modifiers are special characters appended to the ATD command which
instruct the modem how to place a call.
digital signa l. A discrete signal which can only take on one of several (usually only two)
discrete levels in contrast to analog signals which can take a continuous range of levels.
E
error detection and correction . The transmitting modem attaches a special pattern (called a
frame check sequence) calculated according to a prescribed algorithm from user-defined data to
the end of a block of data. The receiving modem performs the same algorithm and compares it
to the one with the transmitted data. If these match, then the block of data has been received
correctly. If not, the block of data is re-transmitted until no errors are detected.
escape sequence . Also referred to as the escape command. This special command is entered as
three plus symbols (+++) and places the modem in command mode and interrupts user data
transmission, but does not terminate the data connection. This allows the entering of commands
while the connection is maintained.
extended AT-command . Extended commands were developed to provide greater functionality
and control over modem operations than is available from the basic AT command set.
F
fax mode . The modem is in fax mode when, through use of fax communications software, it can
send and receive faxes, print and display fax files, convert files to fax-files, and set certain fax-
related features. Note: the modulation protocol used by the modem in fax mode is also different
from the usual data mode modulation.
flow control
. Compensates for the difference between the rate at which data reaches a device
and the rate at which the device processes and transmits. The two common types of flow control
are RTS/CTS signaling (a hardware based method, employing an electrical signal) and XON/
XOFF (a software-based method using standard ASCII control characters to pause or resume
transmission). The \G command controls XON/XOFF flow control.
full-duplex
. Two-way simultaneous transmission between modems, which may occur via a
four-wire circuit on a leased line, or with a two-wire connection when the frequency bandwidth
is divided into two distinct channels, or when echo cancellation is employed (e.g., Bell 103, 212,
and V.22 use frequency division, while V.32 uses echo cancellation).
G
guard tone . Guard tones are used in the United Kingdom and other countries. This requires that
the modem transmit an 1800-Hz tone after it sends an answer tone. The guard tone is controlled
by the &G command. Guard tones are not used in the U.S.A.