Multi-Tech MultiModem ISIHI-2S, Manual

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MultiModemISI Hybrid Series, ISIHI-2S 173
Glossary
Data compression: The process of reducing the data bits
necessary to represent useful information. By compressing
files, less storage is required and higher throughputs are
realized.
Data Pump: The DAC (Digital-to-Analog Conversion)
circuitry used within a modem.
DB-25: A very common 25-pin connector often referred to
as an RSs-232 connector because it is the connector over
which the RS-232 interface commonly occurs.
DB (Direct Current): 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 consen-
sus of the industry and users for a particular aspect of
manufacturing. CCITT’s V and X standards (V.32 and
Xx.25) are examples of de jure standards. Compare with de
factor standards.
Decibel (dB): A unit of measurement for signal strength
based on logarithmic increments, A decibel is a relative
measurement that is derived from an initial reference level
and a final observed level.
Default: A preset value or option, in software packages, or
in hardware configuration, 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 that
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: A set of tiny toggle switches, built into a DIP
(dual in-line package), used for setting configurable param-
eters on a PCB (printed circuit board).
Directory: A logical subdivision of a computer’s disk space
used to organize a group of files. A directory can be thought
of as a file drawer.
DOS (Disk Operating System - pronounced “daws”):
The software that allows all the hardware in a PC to inter-
act. The basis for (DOS prompt) higher level applications.
DOS prompt: The > symbol displayed after the disk drive
letter.
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.
Driver: A software module that interfaces between the
Operating System and a specific hardware device, such as
a color monitor, printer or hard disk. Also known as a device
driver.
DSR (Data Set Ready): An RS-232 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.
DTMF (Dual-Tone MultiFrequency): A generic push-button
concept made popular by AT&T TouchTone.
DTR (Data Terminal Ready): An RS-232 signal sent from
the computer or terminal to the modem indicating that it is
able to accept data.
E
EBCDIC (Extended Binary Coded Decimal Interchange
Code - pronounced “eb suh dick”): An IBM character
code used in its mainframe and midrange computers. It is
an 8-bit code (256 combinations) that stores one alphanu-
meric character or two decimal digits within a byte. EBCDIC
and ASCII codes are the most common codes used to
represent data.
Echo: The reflection or duplication of a signal back toward
its source. Echoing is useful when a terminal is transmitting
data, in that the data can be echoed to the screen so the
user can monitor what is being sent. Echoing is undesirable
when it refers to the signal which results on a telephone line
from impedance mismatches.
Echo cancellation: a high speed modem technique that
isolates and filters out unwanted signals caused by echoes
from the main transmitted signal. This allows full-duplex
modems to send and receive on the same frequency
carrier.
EIA (Electronics Industries Association); A membership
organization founded in 1924 that includes manufacturers of
electronic parts and systems. With over 1200 members, it
sponsors shows and seminars, gives awards for outstand-