Multi-Tech ISIHI-2S Specifikace stáhnout pdf (Strana 176)

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

Glossary

checksumA control field found in synchronous data

packets which contain the results of the error control

algorithm used.

chipAlso called integrated circuits (IC), they are squares or

rectangles that contain from a few dozen to a few million

electronic components.

CHKDSK (pronounced check disk)External DOS com-

mand that reports free memory and disk space. CHKDSK

must be run directly from DOS or within a batch file.

circuitAny closed path through which electrical current can

flow.

circuit-switched networkA technology used by the PSTN

that allocates a pair of conductors for the exclusive use of

one communication path. Circuit switching allows multiple

conversations on one talk path only if the end-users

multiplex the signals prior to transmission.

circuit switchingThe temporary connection of two or more

communications channels using a fixed, non-shareable path

through the network. Users have full use of the circuit until

the connection is terminated.

clipboardAn electronic holding place for the most recent

cur or copy made from a document. Whatever is on the

clipboard can be pasted into the current document. Only

one item may be on the clipboard at a time. When new copy

is sent to the clipboard the existing copy is eliminated.

When you shut down your computer, whatever is on the

clipboard is lost.

clockA timing signal generated by an oscillating circuit that

is used to synchronize data transmissions.

commandAn instruction that tells a computer to begin,

continue, or end a specific operation.

command modeOne of two states of an intelligent (pro-

grammable) device. The mode in which commands can be

issued to alter operating parameters.

communications serverAlso known as the Async Gateway,

it is a PC equipped with the appropriate hardware and

software package so it can function as a gateway between a

LAN and its modems or host connections.

COMx portA serial communications port on a PC.

CONFIG.SYS file (pronounced config dot sis)A text file

that contains configuration commands used when you start

your computer. Commands in the CONFIG.SYS file enable

or disable system features, set limits or resources, and

extend the operating systems purpose by loading device

drivers.

cooked dataA term used in UNIX communications to

identify the UNIX command-line data transmitted. This

type of data is noted for a reduction in effective throughput

because it has to be processed, or cooked prior to

transmission. Compare with raw data.

CPU (central processing unit)The computing part of the

computer. It is made up of the control unit and the ALU

(arithmetic logic unit). The CPU, clock and main memory

make up a computer. When you turn on your computer, an

electrical signal follows a permanently programmed path to

the CPU to clear the leftover data from the chips internal

memory registers.

CRC (cyclic redundancy check)A field used in packetized

data that contains two 8-bit BCCs (block check characters)

as the binary result of an algorithm performed on the data

bits in the packet. A CRC is used for error detection by

many synchronous protocols.

CTS (clear to send)With communications between mo-

dems, an RS-232 signal sent from the modem to the DTE

that indicates it is ready to accept data. Contrast with RTS.

DAA (data access arrangement)The circuitry to isolate any

device from phone lines and their associated equipment.

daisy chainA method of connecting multiple devices in a

series, one after another.

data compressionThe process of reducing the data bits

necessary to represent useful information. By compressing

files, less storage is required and higher throughputs are

realized.

data pumpThe DAC (digital-to-analog conversion)

circuitry used within a modem.

DB-25A very common 25-pin connector often referred to

as an RS-232 connector because it is the connector over

which the RS-232 interface commonly occurs.

DB (direct current)Usually understood to mean a constant

voltage supply that fluctuates only a nominal amount. An

analog or digital signal that may vary in voltage level, but it

never crosses the reference voltage (usually called ground).

Contrast with AC.

de facto standardsA de facto standard is one of two types

of voluntary standards recognized by a given market. It is

introduced by a single vendor and becomes a standard by

its widespread use and acceptance by other vendors.

AT&Ts Bell 212A, IBMs Binary Synchronous Protocol,

or DECs VT-100 terminal protocol are examples of de

facto standards. Compare with de jure standards.

de jure standardsA de jure standard is one of two types of

voluntary standards. It represents the collective consensus

of the industry and users for a particular aspect of manufac-

turing. CCITTs V and X standards (V.32 and Xx.25) are

examples of de jure standards. Compare with de factor

standards.

decibel (dB)A unit of measurement for signal strength

based on logarithmic increments, A decibel is a relative

measurement that is derived from an initial reference level

and a final observed level.

defaultA preset value or option in software packages or in

hardware configuration that is used unless you specify

otherwise.

device driverSoftware that controls how a computer

communicates with a device, such as a printer or mouse.

digital signalDigital devices, such as terminals and

computers, transmit data as a series of electrical pulses that

have discrete jumps rather than gradual changes.

digital transmissionA method of electronic information

transmission common between computers and other digital

devices. Analog signals are waveforms: a combination of

many possible voltages. A computers digital signal may be

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