Category : Communication (modem) tools and utilities
Archive   : SP144MAN.ZIP
Filename : APG.TXT

APPENDIX G. GLOSSARY


Cross-references in the following
definitions are printed in boldface.
Analog Loopback
A modem self-test in which data from the
keyboard or an internal test pattern is
sent to the modem's transmitter,
modulated into analog form, looped back
to the receiver, and demodulated into
digital form.
Analog Signals
Continuous, varying waveforms such as
the voice tones carried over phone
lines. Contrast with digital signals.
Answer Mode
A state in which the modem transmits at
the predefined high frequency of the
communications channel and receives at
the low frequency. The transmit/receive
frequencies are the reverse of the
calling modem, which is in Originate
mode.
Application (application program)
A computer program designed to perform a
specific function, such as a word
processor or a spreadsheet.
ARQ
Automatic Repeat Request. A general
term for error control protocols that
feature error detection and automatic
retransmission of corrupted blocks of
data. See MNP and V.42.
ASCII
American Standard Code for Information
Interchange. A 7-bit binary code (0's,
1's) used to represent letters, numbers,
and special characters such as $, !,
and /.
Asynchronous Transmission
Data transmission in which the length of
time between transmitted characters may
vary. Because the time lapses between
transmitted characters are not uniform,
the receiving modem must be signaled as
to when the data bits of a character
begin and when they end. The addition
of Start and Stop bits to each character
serves this purpose.
Auto Answer
A feature in modems enabling them to
answer incoming calls over the phone
lines without the use of a telephone
receiver.
Auto Dial
A feature in modems enabling them to
dial phone numbers over the phone system
without the use of a telephone trans
mitter.
Baud Rate
The number of discrete signal events per
second occurring on a communications
channel. Although not technically
accurate, baud rate is commonly used to
mean bit rate.
Binary Digit
A 0 or 1, reflecting the use of the
binary numbering system (only two
digits). Used because the computer
recognizes either of two states, OFF or
ON. Shortened form of binary digit is
bit.
Bit Rate
The number of binary digits, or bits,
transmitted per second (bps).
Communications channels using telephone
channel modems are established at set
bit rates, commonly 300, 1200, 2400,
4800, 9600, and 14,400.
BPS
The bits (binary digits) per second
rate. Thousands of bits per second are
expressed as kilobits.
Buffer
A memory area used as temporary storage
during input and output operations. An
example is the modem's command buffer.
Byte
A group of binary digits stored and
operated upon as a unit. A byte may
have a coded value equal to a character
in the ASCII code (letters, numbers), or
have some other value meaningful to the
computer. In user documentation, the
term usually refers to 8-bit units or
characters. 1 kilobyte (Kbyte) is equal
to 1,024 bytes or characters; 640 Kbytes
indicates 655,360 bytes or characters.
Carrier
A continuous frequency that can either
be modulated or impressed with another
information-carrying signal. Carriers
are generated and maintained by modems
via the transmission lines of the
telephone companies.
CCITT
An international organization that
defines standards for telegraphic and
telephone equipment. For example, the
Bell 212A standard for 1200-bps
communication in North America is ob
served internationally as CCITT V.22.
For 2400-bps communication, most U.S.
manufacturers observe V.22 bis. The ini
tials CCITT represent the French name;
in English it's known as the
International Telegraph and Telephone
Consultative Committee.
Character
A representation, coded in binary
digits, of a letter, number, or other
symbol.
Characters Per Second
A data transfer rate generally estimated
from the bit rate and the character
length. For example, at 2400 bps, 8-bit
characters with Start and Stop bits (for
a total of ten bits per character) will
be transmitted at a rate of
approximately 240 characters per second
(cps). Some protocols, such as the
Sportster's error-control protocols,
employ advanced techniques such as
longer transmission frames and data
compression to increase cps.
Class 1/EIA-578
An American standard used between
facsimile application programs and
facsimile modems for sending and
receiving faxes.
Cyclic Redundancy Checking (CRC)
An error-detection technique consisting
of a cyclic algorithm performed on each
block or frame of data by both sending
and receiving modems. The sending modem
inserts the results of its computation
in each data block in the form of a CRC
code. The receiving modem compares its
results with the received CRC code and
responds with either a positive or
negative acknowledgment. In the ARQ
protocols implemented in the Sportster
14,400, the receiving modem accepts no
more data until a defective block is
received correctly.
Data Communications
A type of communications in which
computers and terminals are able to
exchange data over an electronic medium.
Data Compression Table
A table of values assigned for each
character during a call under MNP5 data
compression. Default values in the
table are continually altered and built
during each call: the longer the table,
the more efficient throughput gained.
Data Mode
The mode in which the fax modem is
capable of sending and receiving data
files. A standard modem without fax
capabilites is always in data mode.
DCE
Data Communication (or Circuit-
Terminating) Equipment, such as dial-up
modems that establish and control the
data link via the telephone network.
Default
Any setting assumed, at startup or
reset, by the computer's software and
attached devices, and operational until
changed by the user.
Detect Phase
In the CCITT V.42 error-control
protocol, the first stage in estab
lishing if both modems attempting to
connect have V.42 capability.
Dictionary
The term used for compression codes
built by the V.42 bis data compression
algorithm.
Digital Loopback
A test that allows a remote user to run
a diagnostic of your modem's receiver
and transmitter. The Transmit and
Receive circuits at your modem's serial
port are not used.
Digital Signals
Discrete, uniform signals. In this
manual, the term refers to the binary
digits 0 and 1.
DTE
Data Terminal (or Terminating)
Equipment. Usually, a computer or
terminal that generates or is the final
destination of data.
Duplex
Indicates a communications channel
capable of carrying signals in both
directions. See Half Duplex, Full
Duplex.
EIA
Electronic Industries Association, which
defines electronic standards in the U.S.
Error Control
Various techniques that check the
reliability of characters (parity) or
blocks of data. V.42 and MNP error-
control protocols use error detection
(CRC) and retransmission of errored
frames (ARQ).
Facsimile
A method for transmitting the image on a
printed page from one point to another.
Commonly referred to as Fax.
Fax Mode
The mode in which the fax modem is
capable of sending and receiving files
in a facsimile format.
Flow Control
A mechanism that compensates for
differences in the flow of data input to
and output from a modem or other device.
Frame
A data communications term for a block
of data with header and trailer
information attached. The added
information usually includes a frame
number, block size data, error-check
codes, and Start/End indicators.
Full Duplex
Signal flow in both directions at the
same time. In microcomputer
communications, may refer to the
suppression of the online Local Echo.
Half Duplex
Signal flow in both directions, but only
one way at a time. In microcomputer
communications, may refer to activation
of the online Local Echo, which causes
the modem to send a copy of the
transmitted data to the screen of the
sending computer.
Hz
Hertz, a frequency measurement unit used
internationally to indicate one cycle
per second.
IRQ
Interrupt ReQuest. IRQs in the computer
are used to interrupt hardware and
software when there is an event that
requires attention, such as data
arriving at the serial port.
LAPM
Link Access Procedure for Modems, an
error-control protocol defined in CCITT
Recommendation V.42. Like the MNP proto
cols, LAPM uses cyclic redundancy
checking (CRC) and retransmission of
corrupted data (ARQ) to ensure data
reliability.
Local Echo
A modem feature that enables the modem
to display keyboard commands and
transmitted data on the screen.
MNP
Microcom Networking Protocol, an
asynchronous error-control protocol
developed by Microcom, Inc., and now in
the public domain. The protocol ensures
error-free transmission through error
detection (CRC) and retransmission of
errored frames. The Sportster 14,400
uses MNP Levels 2O4 and Level 5 data
compression, which are incorporated into
CCITT Recommendation V.42.
Modem
A device that transmits/receives
computer data through a communications
channel such as radio or telephone
lines. The Sportster 14,400 is a
telephone channel modem that modulates,
or transforms, digital signals from a
computer into the analog form that can
be carried successfully on a phone line.
It also demodulates signals received
from the phone line back to digital
signals before passing them to the
receiving computer.
Nonvolatile Memory (NVRAM)
User-programmable random access memory
whose data is retained when power is
turned off. Used in Sportster 14,400
modems to store a user-defined default
configuration loaded into random access
memory (RAM) at power-on and reset, and
including a stored phone number.
OFF/ON Hook
Modem operations that are the equivalent
of manually lifting a phone receiver
(taking it off hook) and replacing it
(going on hook).
Online Fallback/Fall Forward
A feature that allows high-speed, error-
control modems to monitor line quality
and fall back to the next lower speed in
a defined range if line quality
degrades; as line conditions improve,
the modems switch up to the next higher
speed.
Originate Mode
A state in which the modem transmits at
the predefined low frequency of the
communications channel and receives at
the high frequency. The
transmit/receive frequencies are the
reverse of the called modem, which is in
Answer mode.
Parallel Transmission
The transfer of data characters using
parallel electrical paths for each bit
of the character, for example, 8 paths
for 8-bit characters. Data is stored in
computers in parallel form, but may be
converted to serial form for certain
operations. See Serial Transmission.
Parity
An error-detection method that checks
the validity of a transmitted character.
Character checking has been surpassed by
more reliable and efficient forms of
block-checking, including Xmodem-type
protocols and the ARQ protocols
implemented in Sportster 14,400 modems.
The same type of parity must be used by
two communicating computers, or both may
omit parity.
Protocol
A system of rules and procedures
governing communications between two or
more devices. Protocols vary, but
communicating devices must follow the
same protocol in order to exchange data.
The format of the data, readiness to
receive or send, error detection and
error correction are some of the opera
tions that may be defined in protocols.
RAM
Random Access Memory. Memory that is
available for use when the modem is
turned on, but that clears of all infor
mation when the power is turned off.
The modem's RAM holds the current
operational settings, a flow control
buffer, and a command buffer.
Remote Digital Loopback
A test that checks the phone link and a
remote modem's transmitter and receiver.
Remote Echo
A copy of the data received by the
remote system, returned to the sending
system and displayed on the screen.
Remote echoing is a function of the
remote system.
ROM
Read Only Memory. Permanent memory, not
user-programmable. The Sportster
14,400's factory settings are stored in
ROM and can be read (loaded) into RAM as
an operational configuration if DIP
switch 7 is DOWN at power on or reset.
Serial Transmission
The transfer of data characters one bit
at a time, sequentially, using a single
electrical path. See Parallel
Transmission.
Start/Stop Bits
The signaling bits attached to a
character before the character is
transmitted during Asynchronous
Transmission.
Terminal
A device whose keyboard and display are
used for sending and receiving data over
a communications link. Differs from a
microcomputer in that it has little or
no internal processing capabilities.
Terminal Mode
A simulation mode required for
microcomputers to transmit data. In
Terminal mode the computer acts as if it
were a standard terminal such as a
teletypewriter, rather than a data
processor. Keyboard entries go directly
to the modem, whether the entry is a
modem command or data to be transmitted
over the phone lines. Received data is
output directly to the screen.
Throughput
The amount of actual user data
transmitted per second without the
overhead of protocol information such as
Start and Stop bits or frame headers and
trailers. Compare characters per
second.
Transmission Rate
Same as Bit Rate.
V.21_Fax
A CCITT standard for making facsimile
connections at 300 bps. U.S. Robotics
and compatible fax devices then transmit
or receive at higher speeds.
V.21_Modem
A CCITT standard for modem
communications at 300 bps. Modems made
in the U.S. or Canada follow the Bell
103 standard. However, the modem can be
set to answer V.21 calls from overseas.
V.22
A CCITT standard for modem
communications at 1200 bps, compatible
with the Bell 212A standard observed in
the U.S. and Canada.
V.22 bis
A CCITT standard for modem
communications at 2400 bps. The
standard includes an automatic link
negotiation fallback to 1200 bps and
compatibility with Bell 212A/V.22
modems.
V.23
A CCITT standard for modem
communications at 1200 bps with a 75-bps
back channel. Sometimes used in the
United Kingdom.
V.25
A CCITT standard for modem
communications that specifies an answer
sequence (2100 Hz and 2250 Hz; also
requiring an 1800-Hz guard tone)
different from the Bell answer tone
(2225 Hz) used in the U.S. and Canada.
V.27 ter
A CCITT standard for facsimile
operations that specifies modulation at
4800 bps, with fallback to 2400 bps.
V.29
A CCITT standard for facsimile
operations that specifies modulation at
9600 bps, with fallback to 7200 bps.
V.32
A CCITT standard for modem
communications at 9600 bps and 4800 bps.
V.32 modems fall back to 4800 bps when
line quality is impaired.
V.32 bis
A CCITT standard that extends the V.32
connection range: 4800, 7200, 9600, 12K
and 14.4K bps. V.32 bis modems fall
back to the next lower speed when line
quality is impaired, fall back further
as necessary, and also fall forward
(switch back up) when line conditions
improve.
V.42
A CCITT standard for modem
communications that defines a two-stage
process of detection and negotiation for
LAPM error control. V.42 also supports
the MNP error control protocol levels
2O4 and MNP5 data compression.
V.42 bis
An extension of CCITT V.42 that defines
a specific data compression scheme for
use during V.42 connections.
Word Length
The number of bits in a data character
without parity, start or stop bits.
Xmodem
The first of a family of error control
software protocols used to transfer
files between modems. These protocols
are in the public domain and are
available from many bulletin board
services.
XON/XOFF
Standard ASCII control characters used
to tell an intelligent device to
stop/resume transmitting data. In most
systems typing -S sends the XOFF
character. Some devices, including the
Sportster 14,400, understand -Q as
XON; others interpret the pressing of
any key after -S as XON.