Glossary
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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)—Upgradable memory chip often
used to store firmware. 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 wit h LT (loop
termination).
exchange—A unit (public or private) that can consist of
one or more central offices established to serv e 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 PBXand PBX.
F
fax (facsimile)—Refers to the bit-mapped rendition of a
graphics-oriented document (fax) or to the electronic
transmis sion of th e 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).
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 accom-
plished 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.
hexadecimal—A base 16 numbering system in which one
character represents a four-bit binary value. Hexadecimal
notation uses the numbers 0–9 and the letters A–F, usually
suffixed by an h (e.g., 4CF h).
I
IDN (Integrated Digital Network)—The culmination of
transmission and switching functions using digital
technology in a circuit-switched telecommunications
network.
IEC (Inter-Exchange Carrier)—A telephone company that is
allowed to provide long distance telephone service between
LATAs, but not within any one LATA. Also called IXC.
IETF(Internet Engineering Task Force)—
A self-organized group of people who make technical and
other contributions to the engineering and evolution of the
Internet and its technologies. It is the principal body engaged
in the development of new Internet standard specifications.
I-mux (inverse multiplexer)—A device that will dial up and
combine several lower speed circuits into a virtual broadband
circuit. It takes any multiple up to an aggregate bandwidth,
giving users bandwidth on demand for videoconferencing,
LAN-to-LAN connections, etc. In ISDN devices, inverse
multiplexing is performed by the BONDING prot ocol.
in-band signaling—A technique in which connection
control information is sent over the same channel as
assigned to the subscriber for end-to-end communication.
Two common examples are DTMF line sig naling and M F
trunk signaling.
Internet—A computer network consisting of many millions
of university, government, and private users around the
world. Internet address—A unique 32-bit address for a
specific TCP/IP host on a network. Normally printed in dotted
decimal format (e.g., 129.128.44.227).
I/O address—A location within the I/O address space of your
computer used by a device, such as an expansion card, a
serial port, or an internal modem. The address is used for
communication between software and a device.
IP address—A unique 32-bit address for a specific TCP/IP host
on a network. Normally printed in dotted decimal format
(e.g., 129.128.44.227).
IRQ (interrupt request)—The notification a processor receives
when another portion of the computer’s hardware requires
its attention. IRQs are numbered so that the device issuing
the IRQ can be identified, and so that IRQs can be
prioritized.
ISA (Industry Standards Architecture)—Pronounced ice-a.
The classic 8- or 16-bit architecture introduced with IBM’s
PC-AT computer. Due to speed constraints, IBM later
introduced a restructured Micro Channel Architecture with a
32-bit bus and increased addressing capabilities.
ISDN (Integrated Services Digital Network)—International
telecommunications standard for transmitting voice, video and
data over a digital communications line.
ITU-T (formerly CCITT)—International Telecommunications
Union–Telecommunications Sector; the United Nations