Multi-Tech ISIHI-2S Specifikace stáhnout pdf (Strana 174)

174 MultiModemISI Hybrid Series, ISIHI-2S/2U

Glossary

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 be referred to as a bipolar 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 communica-

tions 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 messages 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 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 electric signals

to be carried on a telephone line.

analog transmissionsOne of two types of telecommunica-

tions 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 nonprofit,

nongovernment 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.

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 hardware. A

software module which provides a uniform interface for

otherwise incompatible programs.

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 charac-

ters. 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 that enables the modem to

go off-hook when it detects an incoming call.

auto dialSome modems provide this feature for asynchro-

nous 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.

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

configure the system.

automatic dialerA device that is programmed to place a

call to a predetermined number any time it is taken off-

hook.

backgroundAn activity that takes place in the PC while

you are running another application. In other words, the

active user interface does not correspond to the back-

ground task. In Windows, the area behind the active

window. Compare with foreground.

backupAdditional resources or duplicate copies of data on

different storage media for emergency purposes.

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