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Glossary
device address: the address of a device on the Universal Serial Bus. The Device Address is the Default Address when the Universal
Serial Bus device is first powered or reset. Hubs and functions are assigned a unique Device Address by Universal Serial Bus software.
device driver—Software that controls how a computer communicates with a device, such as a printer or mouse.
digital data—Information represented by descrete values or conditions (contrast

analog data

).
digital PBX—A private branch exchange that operates internally on digital signals. See also
exchange
.
digital signal— A discrete or discontinuous signal (e.g., a sequence of voltage pulses). Digital devices, such as as a series of electrical
pulses that have discrete jumps rather than gradual changes.
digital transmission—A method of electronic information transmission common among computers and other digital devices. Because a
digital signal may be only

high

or

low

at any given time, noise and distortion can easily be removed from digital transmissions.
digitize—To convert an analog signal to a digital signal.
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 printed circuit board.
DN (directory number)—The phone number assigned to an ISDN TA at subscription time. It is a string of up to 24 characters, consisting of
the valid dialing characters (0-9, *, and #).
driver—A software module that interfaces between the operating system and a specific hardware device (e.g., color monitors, printers,
hard disks, etc.). Also known as a device driver.
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 that usually refers to PCs, terminals, printers, etc.
DTMF (dual-tone multifrequency)—A generic push-button concept made popular by AT&T TouchTone.
DTMF detection—A capability in some fax/data modems that can differentiate between DTMF or fax calling tones. A typical application
would be a program that routes calls to specific communications applications, depending either on the type of call or on a DTMF tone added
to a dialing string.
E
EEPROM (electrically eraseable programmable read-only memory)—A permanent memory chip that can be reprogrammed by the customer
after the manufacturer has set initial values. See also

ROM

.
EISA (Enhanced Industry Standard Architecture)—Pronounced

eesa

. The purpose of the EISA bus is to provide a 32-bit bus for faster
throughputs while maintaining backward compatibility with the classic ISA bus architecture.
ET (exchange termination)—The carrier’s local exchange switch. Contrast with

LT (loop termination)

.
exchange—A unit (public or private) that can consist of one or more central offices established to serve a specified area. An exchange
typically has a single rate of charges (tariffs) that has previously been approved by a regulatory group.
exchange area—A geographical area with a uniform set of charges (tariffs), approved by a regulatory group for telephone services. Calls
between any two points within an exchange area are local calls. See

digital PBX

and

PBX

.
F
fax (facsimile)—Refers to the bit-mapped rendition of a graphics-oriented document (fax) or to the electronic transmission of the image
over telephone lines bit-mapped approximation of a graphical document and, therefore, cannot be accurately interpreted according to any
character code.
firmware—Software that is stored in read-only memory (ROM). Unlike random access memory (RAM), ROM can retain its content without
electrical power. Some ROM, known as EEPROM, can be reprogrammed electrically while it is in a device.
foreground—The application program currently running on and in control of the PC screen and keyboard. The area of the screen that
occupies the active window. Compare with

background

.
frequency—A characteristic of an electrical or electronic signal which describes the periodic recurrence of cycles. Frequency is inversely
proportional to the wavelength or pulse width of the signal (e.g., long wavelength signals have low frequencies and short wavelength signals
yield high frequencies).
function: A Universal Serial Bus device that provides a capability to the host. For example, an ISDN connection, a digital microphone, or
speakers.
H
handshaking—A process that two modems go through at the time of call setup to establish synchronization over the data communications
link. It is a synchronization and negotiation process accomplished by the exchange of predefined, mutually recognized control codes.
HDLC (High-Level Data Link Control)—An ISO standard, bit-oriented data communications protocol that provides nearly error-free data
transfers.