Multitech MMH900 User Manual page 185

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 bipolar
signal. Contrast with DC.
ACK (ACKnowledgement code) (pro-
nounced "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. Contrast with
NAK.
Address: A numbered location inside a
computer. It's how the computer accesses its
resources, like a video card, serial ports,
memory, etc.
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 continuous 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
electrical signals to be carried on a telephone
line.
Analog Transmission: One of two types of
telecommunications 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) (pronounced "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 punctuation and
the second 128 contain math and foreign
language symbols.
ASCII (American Standard Code for
Information Interchange) (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.
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
transmission between a computer and a
modem. One character at a time, encoded
into a series of electrical pulses, is transmitted
or received. This the oldest method of data
transfer. When it is used with error correcting
software and data compression algorithms,
along with the increase in maximum attainable
speeds, it continues to be a viable alternative
to synchronous transmission..
Auto Dial: Some modems provide this
feature for asynchronous dialing. This feature
is a predefined 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.