Specifications

MultiModem ISI Hybrid Series, ISIHI-2S/2U 175
Glossary
bandRange of frequencies between two defined endpoints.
bandwidthThe transmission capacity of a computer
channel, communications line or bus. It is expressed in
cycles per second (hertz), the bandwidth being the differ-
ence between the lowest and highest frequencies transmit-
ted. The bandwidth of a phone line is about 3000 Hz with
QAM, you get up to 14,400 bps. Bandwidth is often stated
in bits or bytes per second.
baseband signalAn unmodulated signal which is transmit-
ted at its original frequency and may be digital or analog.
baudRate, the signaling rate of a line, the switching speed,
or the number of transitions (voltage or frequency changes)
that are made per second. Transmission speeds are often
expressed in baud, though bits per second is more accurate.
The speed at which your computer talks to your modem.
BCC (block check character)An error control method used
in character-oriented or byte-synchronous protocols. Two 8-
bit BCCs are used to create the CRC (cyclic redundancy
check) field of a synchronous data packet.
Bell 103The U.S. modulation standard for 300bps full-
duplex transmission over dial-up lines.
Bell 201The U.S. modulation standard for 2400bps half-
duplex transmission over dial-up lines or full-duplex
transmission over 4-wire lines. Primarily used in synchro-
nous modems.
Bell 202The U.S. modulation standard for
0-1200bps, half-duplex transmission over 2-wire, or full-
duplex transmission over 4-wire leased lines.
Bell 208The U.S. modulation standard for 4800bps, half-
duplex transmission over dial-up lines, or full-duplex
transmission over 4-wire lines. Primarily used in synchro-
nous modems.
Bell 212AThe U.S. modulation standard for 1200bps full-
duplex transmission over dial-up lines.
binaryA numbering system based on two digits, 1 and 0,
which is conductive to the two-state digital electronics used
within computers. All input to a computer is encoded as a
binary value. Binary also refers to a file format that uses 8-
bit characters , to allow for control characters (i.e., all non-
ASCII files).
BSC (binary synchronous communicationsAlso called
bisync, this communications protocol was the first synchro-
nous data format used by IBM. It is still in use, but is
rapidly being replaced by IBMs newer synchronous data
link control (SDLC). Bisync is a byte-synchronous protocol
that has longer delays and more overhead that the bit-
synchronous SDLC. It uses two synchronization characters
to head every packet.
bit (Binary digIT)A bit is the basis of the binary number
system. It can take the value of 1 or 0. Bits are generally
recognized as the electrical charge generated or stored by a
computer that represents some portion of usable informa-
tion.
bit-synchronous transmissionA synchronous form of data
transmission that focuses on a maximum packet size rather
than the length of the characters the packet contains. SDLC
is a bit-synchronous protocol.
bootStarting or restarting your PC. This term originates
from the saying to pull oneself up by the bootstraps.
bps (bits per second)A unit to measure the speed at which
data bits can be transmitted or received. Bps differs from
baud when more than one bit is represented by a single
cycle of the carrier.
break-out boxAn electronic device which is inserted
between two RS232/V.24 connectors for the monitoring of
pin activity and for the rerouting of lines (crossover).
broadcastTo send information simultaneously to a group of
recipients.
bufferA temporary storage register or random access
memory (RAM) used in all aspects of data communications
that prevents data from being lost due to differences in
transmission speed. Keyboards, serial ports, muxes and
printers are a few examples of the devices that contain
buffers. A buffer allows one device to dump data at a high
speed and for the lower-speed device to accept it at its own
pace. In this way, the high-speed device can continue to
work without having to wait for its data transfer to end.
Buffers are a way of preventing potential data loss.
busA common channel between hardware devices either
internally between components in a computer, or externally,
between stations in a communications network.
byteThe unit of information a computer can handle at one
time. The most common understanding is that a byte consist
of 8 binary digits (bits), because thats what computers
(PCs) can handle. A byte holds the equivalent of a single
character, such as the letter A.
C
CAD (computer aided design, pronounced kad)A comput-
erized system used to design products. CAD systems are
high speed workstations or PCs that use CAD software and
input devices, such as graphic tables and scanners.
callback securityA security feature available in some
intelligent modems that stores phone numbers. When
activated, the user calling the secured modem must furnish
a recognized password and then provide a code that
corresponds to one of the stored phone numbers. When
these security measures are met, the secured modem hangs
up on the caller and dials the appropriate number to
establish a data communications link.
capacitorAn electronic device that stores an electrical
charge. It comes in varying sizes for use in anything from
power supplies to the tiny cells in dynamic RAM chips.
When the device is powered down, its capacitors lose their
charge.
carrier signalAn analog signal with known frequency,
amplitude and phase characteristics used as a transport
facility for useful information. By knowing the original
characteristics, a receiver can interpret any changes as
modulations, and thereby recover the information.
character setOne of a number of coding schemes which
uses binary digits to represent characters, numbers, punc-
tuation, and/or control characters. Common character sets
are ASCII, ANSI, and EBCDIC.