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170 MultiModem ISI Hybrid Series, ISIHI-2S
Glossary
A
AC (Alternating Current): A power source whose signal
crosses a reference voltage (usually called ground or zero).
Alternating between a maximum and minimum voltage, AC
may also be referred to as a bi-polar signal.Contrast with
DC.
ACK (ACKnowledgment code – pronounced “ack”): A
communications code sent from a receiving modem to a
transmitting modem to indicate that it is ready to accept
data. It is also used to acknowledge the error-free receipt of
transmitted data. Contract with NAK.
ACS (Asynchronous Communications Server): A
communications server that managers a pool of modems
for shared use over the LAN. It directs outgoing messages
to the next available modem and directs incoming mes-
sages to the appropriate workstation. It also provides
conversion between LAN packets and asynchronous
format.
Address: A numbered location inside a computer. It’s how
the computer addresses its resources, like a video card,
serial ports, memory, etc.
Algorithm: A set of ordered steps for solving a problem.
This can be a mathematical formula or the instruction in a
computer program.
Alphanumeric: The basic character set which includes the
letters A to Z (and a to z) and the digits 0 to 9.
Amplitude: The difference between the maximum and
minimum voltages of a waveform expressed as a “peak-to-
peak” voltage.
Amplifier: An active device within a circuit which increases
the voltage level of all signals (desirable and undesirable).
Analog loopback: A modem diagnostic used to test either
the local analog loop (the modem’s internal circuitry) or the
remote analog loop (the telephone line). The local analog
loop test is accomplished by activating the self-test mode
and tying the modem’s modulator to its demodulator and
examining the return stream of data at the PC or terminal it
services. The remote analog loopback can only be activated
on four-wire leased line connections with a remote modem
capable of performing the same test.
Analog signal: A waveform which has amplitude, frequency
and phase, and which takes on a range of values between
its maximum and minimum points. Analog implies continu-
ous movement from point A to point B, as opposed to
discrete jumps. For example, sound is continuously varying
air vibrations and is converted into analogous electric
signals to be carried on a telephone line.
Analog Transmissions: One of two types of telecommuni-
cations which uses an analog signal as a carrier of voice,
data, video, etc. An analog signal becomes a carrier when it
is modulated by altering its phase, amplitude and frequency
to correspond with the source signal. Compare with digital
transmission.
ANSI (American National Standards Institute – pro-
nounced “ansy”): A U.S. standards organization supported
by over 1000 companies and trade organizations. It is a
non-profit, non-government group that is the U.S. member
of the ISO (International Standards Organization).
ANSI character set: An 8-bit character set that contains
256 characters. The first 128 characters are alphanumeric
and the second 128 contain math and foreign language
symbols.
API (Application Programming Interface): The language
and message format used by a program to activate and
interact with functions in another program or in the hard-
ware. A software module which provides a uniform interface
for otherwise incompatible programs.
ASCII (American Standard Code for Information Inter-
change – pronounced “askey”): A binary code for data
that is used in communications and in many computers and
terminals. The code is used to represent numbers, letters,
punctuation and control characters. The basic ASCII code is
a 7-bit character set, which defines 128 possible characters.
The extended ASCII file provides 255 characters.
Associate: Establishing that all files with a given extension
are usable by a certain application.
Asynchronous Transmission: The transmission of data in
which each character is a self-contained unit with its own
start and stop bits. This is a common method of transmis-
sion between a computer and a modem. One character at a
time, encoded into a series of electrical pulses, is transmit-
ted or received. This is the oldest method of data transfer.
When it is used with error correcting software and data
compression algorithms, along with the increase it maxi-
mum attainable speeds, it continues to be a viable alterna-
tive to synchronous transmission.
ATM (Asynchronous Transfer Mode): A high speed
switching technique suitable for MAN’s (Metropolitan Area
Network) and broadband ISDN transmission.
Auto Answer: A modem feature which enables the modem
to “off-hook” when it detects an incoming call.
Auto Dial: Some modems provide this feature for asyn-
chronous dialing. This feature is a pre-defined macro that
allows the user to enter the location of a phone number (i.e.
N0 through N9) and have the modem go off-hook, dial and
establish the connection. With the auto dial feature, an
asynchronous terminal can establish a dialing directory
without running a communication software package.
AUTOEXEC.BAT (AUTOmatic EXECute BATch): A DOS
batch file that executes when the computer is started. This
file contains the basic start-up commands that help config-
ure the system.