Multitech MMH900 User Manual page 187

Circuit switching: The temporary connec-
tion of two or more communications channels
using a fixed, non-shareable path through the
network. Users have full use of the circuit
until the connection is terminated.
Clock: A timing signal generated by an
oscillating circuit which is used to synchronize
data transmissions.
Command: An instruction that tells a
computer to begin, continue or end a specific
operation.
Command mode: One of two states of an
intelligent (i.e. programmable) device. The
mode in which commands can be issued to
alter operating parameters.
CRC (Cyclic Redundancy Check): A field
used in packetized data that contains two 8-bit
BCCs ( Block Check Characters) as the binary
result of an algorithm performed on the data
bits in the packet. A CRC is used for error
detection by many synchronous protocols.
CTS (Clear To Send signal): With communi-
cations between modems, an RS-232 signal
sent from the modem to the DTE that
indicates it is ready to accept data. Contrast
with RTS.
D
DC (Direct Current): This is usually
understood to mean a constant voltage supply
that fluctuates only a nominal amount. An
analog or digital signal that may vary in
voltage level, but it never crosses the
reference voltage (usually called ground).
Contrast with AC.
De facto standards: A de facto standard is
one of two types of voluntary standards
recognized by a given market. It is introduced
by a single vendor and becomes a standard
by its widespread use and acceptance by
other vendors. AT&T's Bell 212A, IBM's
Binary Synchronous Protocol or DEC's VT-
100 terminal protocol are examples of de
facto standards. Compare with de jure
standards.
De jure standards: A de jure standard is one
of two types of voluntary standards. It
represents the collective consensus of the
industry and users for a particular aspect of
manufacturing. CCITT's V and X standards
(e.g. V.32 and X.25) are examples of de jure
standards. Compare with de facto standards.
Decibel (dB): A unit of measurement for
signal strength based on logarithmic incre-
ments. A decibel is a relative measurement
that is derived from an initial reference level
and a final observed level.
Default: This is preset value or option in
software packages, or in hardware configura-
tion, that is used unless you specify
otherwise.
Device driver: Software that controls how a
computer communicates with a device, such
as a printer or mouse.
Digital signal: Digital devices, such as
terminals and computers, transmit data as a
series of electrical pulses which have discrete
jumps rather than gradual changes.
Digital Transmission: A method of
electronic information transmission common
between computers and other digital devices.
Analog signals are waveforms: a combination
of many possible voltages. A computer's
digital signal may be only "high" or "low" at
any given time. Therefore, digital signals may
be "cleaned up" (noise and distortion
removed) and amplified during transmission.
DIP switch (pronounced "dip switch"): A
set of tiny toggle switches, built into a DIP
(dual in-line package), used for setting
configurable parameters on a PCB (printed
circuit board).
DPSK (Differential Phase Shift Keying): A
common form of phase modulation used in
modems. It does not require complex
demodulation circuitry and is not susceptible
to random phase changes in the transmitted
waveform, thus reducing errors during
transmission.
DSR (Data Set Ready): An RS232 signal
sent from the modem to the computer or
terminal indicating that it is able to accept
data. Contrast with DTR.
DTE (Data Terminating Equipment): A term
used to include any device in a network which
generates, stores or displays user information.
DTE is a telecommunications term which
usually refers to PCs, terminals, printers, etc.