Modems - Networking;
Glossary of Terms
A B
C D E F G H I J K L M N O P Q R S T U V W X Y Z
A
Adaptive Speed Leveling (ASL)
A Courier( feature, first used by V.32 bis and V.32 terbo modems in November 1990, that
detect interference on a line or improved line conditions and shift accordingly. This
feature allows the send and receive channels of a modem connection to adapt independently
to varying line conditions. Each channel shifts down in speed when interference is
detected and back upward again when line conditions improve without affecting the
performance of the other channel. The modems at both ends of the connection adapt
independently, each detecting and adjusting to line conditions. ASL keeps the modems
online, always operating at the highest possible speed, and constantly ensuring data
integrity.
ADPCM
Adaptive Differential Pulse Coded Modulation. This is used in voice compression
algorithms.
AEC
Acoustic Echo Cancellation. This is used in Speakerphone technology.
AGC
Automatic Gain Control. This is used in Speakerphone technology.
AIC
Analog Interface Circuit. Used on all modems.
Aiff
One of many sound file formats for the Macintosh computer.
Anonymous FTP
A manner of logging into an FTP site as a public user. Many FTP sites will allow anonymous
logins to access some files.
ANSI
American National Standards Institute - Generic body for U.S. Standards.
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.
ARQ
Automatic Repeat Request. A general term for error control protocols which feature error
detection and automatic retransmission of defective blocks of data. See HST(, MNP, and
V.42.
ASCII
American Standard Code for Information Interchange. The format used for standard
unformatted text. A 7_bit binary code (0's, 1's) used to represent letters, numbers, and
special characters such as $, !, and /. Supported by almost every computer and terminal
manufacturer.
ASIC
Applications Specific Integrated Circuit. Used on all U.S. Robotics modems.
Asymmetrical Modulation
A duplex transmission technique which splits the communications channel into one high
speed channel and one slower channel. During a call under asymmetrical modulation, the
modem with the greatest amount of data to transmit is allocated the high speed channel.
The modem with less data is allocated the slow, or back channel (450 bits per second
(bps)). The modems dynamically reverse the channels during a call if the volume of data
transfer changes.
Asynchronous Transmission
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. Compare to Synchronous
Transmission.
ATM
Asynchronous Transfer Mode. A network technology based on transferring data in cells or
packets of a fixed size. The cell used with ATM is relatively small compared to units used
with older technologies. The small, constant cell size allows ATM equipment to transmit
video, audio, and computer data over the same network, and assure that no single type of
data hogs the lines. Current implementations of ATM support data transfer rates of from 25
to 622 Mbps (megabits per second).
.au
A sound file format for UNIX systems.
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 transmitter.
AWAN
Analog Wide Area Network
B
Baud Rate
The number of discrete signal events per second occurring on a communications channel. The
communications carrier frequency. Due to advanced coding methods, each signal can carry
more than one bit. At 300 baud, approximately 300 bits are transmitted per second. For
speeds higher than 2400, baud rate and bit rate are no longer equivalent. Although not
technically accurate, baud rate is commonly used to mean bit rate (bps). In communications
software, baud rate refers to the computer’s serial port rate. See UART.
BBS
Electronic Bulletin Board System
Bell 103
A standard for modem data communication at 300 bps. See V.21.
Bell 212A
A standard for modem data communications at 1200 bps. See V.22.
Beta Test
Second stage testing performed by dependable customers who volunteer to use a product and
report any problems, before the product is actually released.
Binary Digit
A 0 or 1, reflecting the use of a 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.
Bisync
Binary Synchronous Control. An earlier protocol developed by IBM for software applications
and communicating devices operating in synchronous environments. The protocol defines
operations at the link level of communications, for example, the format of data frames
exchanged between modems over a phone line. See Protocol, HDLC, SDLC.
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 14400.
Bits per Second
The bits (binary digits) per second rate. A 14,400 Sportster(, for example, is capable of
transmitting 14,400 bits per second to another modem capable of at least 14,400 bps.
BLAST
Data communications software made by CRG, mainly for file transfer and the name of the
file transfer protocol.
BPS
Bits Per Second.
BRI
Basic Rate Interface - 2B+D ISDN connection
Buffer
A memory area used as temporary storage during input and output operations. An example is
the modem's command buffer. Another is the Transmit Data flow control buffer used for flow
control and to store copies of transmitted frames until they are positively acknowledged
by the receiving modem.
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 (K) is equal to 1,024 bytes or characters; 64K indicates 65,536
bytes or characters.
C
Call Link
Software based phone system
CCITT
Formerly, an international organization that defined standards for telegraphic and
telephone equipment. It has been incorporated into its parent organization, the
International Telecommunication Union (ITU). Telecommunication standards are now covered
under Telecommunications Standards Sector (TSS). ITU-T replaces CCITT. For example, the
Bell 212A standard for 1200 bps communication in North America was referred to as CCITT
V.22. It is now referred to as ITU-T V.22.
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 USR-HST and MNP, 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 Class 1 faxes.
Class 2.0/EIA-592
An American standard used between facsimile application programs and facsimile modems for
sending and receiving Class 2.0 faxes.
Client
A computer that connects to a server which exchanges information.
CSLIP
Compressed Serial Line Internet Protocol- A SLIP protocol that compresses the amount of
information in the packet header. Also see SLIP.
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 protocol implemented in U.S. Robotics high speed
modems, the receiving modem accepts no more data until a defective block is received
correctly.
D
Data Communications
A type of communications in which computers and terminals are able to exchange data over
an electronic medium.
Data Compression (Computer)
Storage of programs, files, and data on a hard drive or other storage device in compressed
format so as to require less storage space. Can be done manually using a compression
utility such as PKZIP, or can be done automatically using a utility such as Stacker or
DoubleSpace.
Data Compression (Modem)
When the transmitting modem detects redundant units of data, it recodes them into shorter
units of fewer bits. The receiving modem then decompresses the redundant data units before
passing them to the receiving computer.
DCE
Data Communication (or Circuit-Terminating) Equipment. In this manual, the term applies to
dial-up modems that establish and control the data link via the telephone network.
Dedicated Line
A user-installed telephone line used to connect a specified number of computers or
terminals within a limited area, for example, one building. The line is a cable rather
than a public-access telephone line. The communications channel may also be referred to as
nonswitched because calls do not go through telephone company switching equipment.
Digital Signals
Discrete, uniform signals. In this manual, the term refers to the binary digits 0 and 1.
Domain
A subsection of the internet of an IP address which is most commonly used to refer to a
group of computers whose hostnames share a common suffix: the domain name. The primary
domains are: .COM, .ORG, .NET, .MIL.
Domain name
The information located to the right of the @ in an address, this is also referred to as
DNS. e.g. support@usr.com In this case usr.com is the domain
DNS
Domain Name Server- A system used to translate hostnames like USR.COM to a numeric
Internet address. The DNS will also provide naming for clients as well as hosts.
DSP
Digital Signal Processor. Frequently called the “data pump.” A chip in the
modem’s circuitry that handles all of the actual work of sending and receiving data.
Duplex
Indicates a communications channel capable of carrying signals in both directions. See
Half Duplex, Full Duplex.
E
EEPROM
(Electronically Eraseable Programmable Read Only Memory) replaced ROM in our new models of
modems. This is permanent memory too. The only way that a user can write to this memory is
through an executable program that erases the code written there and new code files
contained in the program are written to the EEPROM. (Also known as EPROM, which is the way
it is listed under ATI7) This makes flashing a modem for an upgrade or update possible.
EIA Standards Committee
Electronic Industries Association, which defines electronic standards in the U.S.
Error Control
Various techniques which check the reliability of characters (parity) or blocks of data.
V.42, MNP and HST error control protocols use error detection (CRC) and retransmission of
frames in error (ARQ). Error control is a required component of data compression.
Error Detection
The process of determining whether errors have been introduced to transmitted data.
Although some people use the terms “error detection” and error correction”
interchangeably, it is important to note that the modem does not perform error correction.
If errors are detected, the receiving modem sends a request for the sending modem to start
over again where the errors where first encountered. Formerly parity was used as a method
of error detection, but as the speed increased and the amount of data increased, this was
not effective.
F
firewall
A system set up to monitor and block certain types of traffic between a network or
networks and the internet. This is mainly set up for security reasons, to prohibit
unauthorized access of confidential information.
Flash ROM
Read Only Memory that can be erased and reprogrammed with software. Most U.S. Robotics
Courier modems can be updated or upgraded using a program downloadable from the U.S.
Robotics BBS when available.
Flow Control
A feature that compensates for differences in the flow of data input to and output from a
modem or other device. Necessary to keep a modem from sending data faster than a computer
can handle it, to prevent overflow and data loss.
FTP
File Transfer Protocol- A protocol used for sending files from one computer to another.
Full Duplex
Signal flow in both directions at the same time. In microcomputer communications, may
refer to the suppression of the online Local Echo. Telephones operate in full duplex, as
they are capable of sending and receiving signals at the same time. See also Simplex,
Duplex, Half Duplex.
G
Gateway
A system by which two incompatible networks or applications can communicate with each
other.
GUI
Graphical User Interface- An interface that is accessed by icons and other graphical
images. Windows and Macintosh systems use a GUI.
H
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. Walkie
talkies use Half Duplex transmission, because they cannot send and receive signals at the
same time.
Header
The part of a data packet which contains the source and destination address of that data
packet. A header is like an envelope for a letter.
HDLC
High Level Data Link Control. A standard protocol developed by the International Standards
Organization for software applications and communicating devices operating in synchronous
environments. The protocol defines operations at the link level of communications, for
example, the format of data frames exchanged between modems over a phone line. See Bisync,
Protocol, SDLC.
Hostname
A unique name by which a computer is known on a network. The hostname is also used to
identify it in electronic mail or other forms of electronic information interchange over a
network or internet.
HST(High Speed Technology)
U.S. Robotics' proprietary signaling scheme, design and error control protocol for
high-speed modems. HST incorporates trellis-coded modulation, for greater immunity from
variable phone line conditions, and asymmetrical modulation for more efficient use of the
phone channel at speeds of 4800 bps and above. HST also incorporates MNP-compatible error
control procedures adapted to asymmetrical modulation.
HTML
Hyper Text Markup Language- The language or format in which Web pages are written.
HTTP
Hyper Text Transport Protocol- The system used to request HTML documents from the World
Wide Web.
Hz
Hertz, a frequency measurement unit used internationally to indicate one cycle per second.
I
Intranet
Intranet is a TCP/IP network inside a company that links that company to the Internet.
Most Intranets are only accessible from within the location or company that runs that
Intranet.
IP Address
All computers on the Internet use IP address for identification purposes. The format of
this address is three dots and four groups of numbers. There is a network number, host
number, and a subnet address. i.e. 1.22.333.44
IPX
Internetwork Packet eXchange- A protocol used to link Local Area Networks to each other
with a router device.
IRC
Internet Relay Chat- The live chat area of the internet.
ISDN
Integrated Switched Digital Network- A digital telephone system which provides noise free
high speed communications. The service is a custom service that must be installed by the
phone company. You will need a Terminal Adapter, a telephone provider which supports ISDN,
and a service provider. Usually telephone exchange carriers use digital lines to
communicate with one another, but it is possible to have one of these digital lines
installed directly into your home or office. Results in higher speed, fewer errors, and
allows for separate lines and communications channels. No analog signal is modulated (no
modem), but usually a Terminal Adapter is required because digital signals differ.
ISP
Internet Service Provider- A company which provides access to the Internet whether it is a
personal dial-up account or a cooperate networked connection. Most ISPs will provide extra
services include help with design, creation and administration Web sites, and intranet
support for companies.
ITU-T
International Telecommunication Union-Telecommunication sector. Formerly referred to as
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 observed internationally as ITU-T V.22. For 2400 bps communication, most U.S.
manufacturers observe V.22 bis.
J
K
L
LAN
Local Area Network- A computer network located in one or more buildings.
LAPM
Link Access Procedure for Modems, an error control protocol incorporated in ITU-T
Recommendation V.42. Like the MNP and HST protocols, LAPM uses cyclic redundancy checking
(CRC) and retransmission of corrupted data (ARQ) to ensure data reliability.
Leased Line
A phone line, leased from the phone company, set up specifically as a direct connection
between two fixed locations. There is no dial tone on these lines. Only Courier modems
support leased lines.
Legacy
A term used to describe products that are
Link
A reference point from one site or location which will point you to another location for
that information.
Listserv
Listserv an automatic email server. This server processes electronic mail requests for
addition to or deletion from mailing lists. Some listservs provide facilities such as
retrieving files from archives and a database search.
Local Echo
A modem feature that enables the modem to send copies of keyboard commands and transmitted
data to the screen. When the modem is in Command mode (not online to another system) the
local echo is invoked through the ATE1 command. The command causes the modem to display
your typed commands. When the modem is online to another system, the local echo is invoked
through the ATF0 command. This command causes the modem to display the data it transmits
to the remote system.
M
MIME
Multipurpose Internet Mail Extension- A file format that will allow you to post non-text
data in a mail message. Graphic files, video, audio, and executables file can be sent via
email using this manner.
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. U.S. Robotics modems
use MNP Levels 4 and Level 5 data compression. MNP Levels 4 have been incorporated into
ITU-T Recommendation V.42. Compare HST.
Modem
The word modem is actually an acronym for modulate and demodulate. A modem is a serial
device that modulates the computer’s digital data into analog signals compatible with
the Public Switched Telephone Network (PSTN) to communicate over an analog telephone line
and demodulates analog signals into digital data to communicate with the computer.
MUD
Multi-User Dungeon- This goes by many other names as well. A format in which games are
played over the internet. This is usually a text based game, but it can be used for
conferencing and educational purposes. They are accessed via telnet or other specialized
client programs.
N
Newsgroups
See USENET
Nonvolatile Memory (NVRAM)
User-programmable random access memory whose data is retained when modem power is turned
off. Used in Courier modems to store a user-defined default configuration loaded into
random access memory (RAM) at power on.
Novell
A company that develops software to allow PC’s to link together using today’s
networking hardware.
NVRAM
(Non-volatile Random Access Memory) is user-programmable random access memory whose data
is retained when modem power is turned off. Used in modems to store a user-defined
configuration which can be loaded into RAM at power on.
O
OEM
Original Equipment Manufacturer.
Online Fallback
A feature that allows high speed error-control modems to monitor line quality and fall
back to the next lower speed if line quality degrades. The modems fall forward as line
quality improves.
P
Packets
A unit of data which is sent through a network. A packet will consist of many layers of
information. Each layer of information will address an aspect of that data packet, from
the “where” and “who” information to the type of information that is
being sent.
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 protocol implemented in Courier modems. The
same type of parity must be used by two communicating computers, or both may omit parity.
When parity is used, a parity bit is added to each transmitted character. The bit's value
is 0 or 1, to make the total number of 1's in the character even or odd, depending on
which type of parity is used.
PC
Personal Computer. Generally refers to an IBM compatible computer (386, 486, Pentium,
etc.).
POP
Post Office Protocol- A protocol designed to read electronic mail from a server. There are
three versions: POP, POP2, and POP3 which are commonly used on today’s computers.
PPP
Point to Point Protocol- An internet protocol used to send packets of internet information
over serial points to point links.
Plug-ins
Plug-ins are software programs that extend the capabilities of your Web browser. They
allow you to play audio, video, and view 3D graphics through your browser.
Proprietary
Exclusively owned, made, and sold by one holding a trademark or patent. HST is a
proprietary protocol of U.S. Robotics.
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 operations that may be defined in protocols.
Q
Queue
A waiting line. For example, in a print queue, if a document is sent by person A, then by
person B, then by person C, the jobs to be printed would be stored in a queue, job A would
be printed, then job B, then job C.
R
RAM
Random Access Memory. Memory that is available for use when the modem is turned on, but
that clears of all information when the power is turned off. The modem's RAM holds the
current operational settings, a flow control buffer, and a command buffer.
Remote Access
A feature that allows a remotely-located user to view the Courier's configuration screens
and change the Courier's configuration. Password protection is available.
RJ11
Technical name for a standard phone cable used by telephones and modems. One RJ11 cable is
supplied with each of our desktop modem products.
RAM
(Random Access Memory) is available for use when the modem is turned on, but clears of all
information when the power is turned off. User may write to this memory. The modem’s
RAM holds the current settings.
ROM
(Read Only Memory) is permanent memory and the user may not write to this memory. The
modem’s factory settings are stored in ROM and can be read (loaded) into RAM as an
operational configuration or current settings.
Router
A device which passes information from one network to another.
S
Serial Port
A nine- or 25- pin male port found on the back of a computer, which, via an RS-232C cable,
connects to the serial port on a modem. Most computers have two serial ports, COM1 and
COM2. A computer’s serial ports are run by UART chips, which come in different
speeds. See UART.
Serial Transmission
The transfer of data characters one bit at a time, sequentially, using a single electrical
path. See Parallel Transmission.
SG
Signal Ground
Shareware
Software that is offered free to try. If the software is used beyond the trial period, it
will need to be registered with the company or individual that produced it. There is
usually a fee for the registration of the software. Most shareware applications are posted
on the Internet, on-line services, and Bulletin Boards.
Simplex (Transmission)
Indicates a comunications system capable of transmitting a signal in only one direction,
for example, an FM radio channel.
SLIC
Subscriber Line Interface Circuit - A standard RJ11 telephone jack
SLIP
Serial Line Internet Protocol- Is used to connect a remote computer to the Internet using
a modem.
SPORTSTER
U.S. Robotics line of desktop modems.
Start/Stop Bits
The signaling bits attached to a character before the character is transmitted during
Asynchronous Transmission.
SDLC
Synchronous Data Link Control. A protocol developed by IBM for software applications and
communicating devices operating in IBM's Systems Network Architecture (SNA). The protocol
defines operations at the link level of communications, for example, the format of data
frames exchanged between modems over a phone line. See Bisync, Protocol, HDLC.
SMTP
Simple Mail Transfer Protocol- One of the protocols under the TCP/IP group of protocols
used to transfer electronic mail between computers.
Synchronous Transmission
A form of transmission in which blocks of data are sent at strictly timed intervals.
Because the timing is uniform, no Start or Stop bits are required. Compare Asynchronous
Transmission. Some mainframes only support synchronous communications unless their owners
have installed a synchronous adapter and appropriate software.
Sysop
A SYStems OPerator. A person who runs a bulletin board (BBS).
T
TA
Terminal Adapter - Used in ISDN connections
TCP/IP
Transmission Control Protocol / Internet Protocol- A protocol that allows you to access
services on the internet such as Telenet, FTP, email and other services.
Telnet
A TCP/IP application that allows you to connect to other host systems on the internet.
Some Bulletin boards can be access via Telnet.
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 no internal processing
capabilities. Used to enter data into or retrieve processed data from a system or network.
Terminal Mode
An operational 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. The more popular communications software products control Terminal mode as
well as enable more complex operations, including file transmission and saving received
files.
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.
Touchbase
Portable modem company which USR acquired in 1991, therefore giving U.S. Robotics its
WorldPort product line.
Transmission Rate
Same as Bit Rate.
TXD
Transmit Data
U
UART
Universal Asynchronous Receiver- Transmitter. The controlling component of a serial port.
There are three common types of UARTs: 8250, 16450, and 16550, which are capable of safe
transmission speeds of 19,200 bps, 38,400 bps, and 57,600 bps respectively, though higher
speeds are sometimes possible. Our internal modems have 16550 UARTs built in. External
modems do not have UARTs.
UNIX
One of many computer operating systems which are used to control a computer. UNIX was the
main operating system of the Internet at one time. There are other operating systems used
on the Internet however UNIX is still popular with many Web developers. UNIX is offered in
many different varieties some are OSF, Version 7, Linux, Xenix, and GNU.
UPDATES
Fixes to existing code of the modem and there is no charge associated with updates.
USENET
User’s Network also referred to as “Newsgroups.” A large collection of
discussion groups on all topics. Messages are posted to these groups as mail messages.
URL
Uniform Resource Locator - Used to point to a particular internet site
USB
Universal Serial Bus - Specification for increasing serial bus throughput.
V
V.8
An ITU-T standard, included with V.34, that sends a signal to the receiving modem to make
the process of connecting faster.
V.17
An ITU-T standard for facsimile operations that specifies modulation at 14.4K bps, with
fallback to 12K bps.
V.21 190 Fax
An ITU-T standard for facsimile operations at 300 bps. U.S. Robotics or compatible fax
devices then transmit or receive at higher speeds.
V.21 190 Modem
An ITU-T 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 ITU-T standard for modem communications at 1200 bps, compatible with the Bell 212A
standard observed in the U.S. and Canada.
V.22 bis
An ITU-T 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
An ITU-T standard for modem communications at 1200 bps with a 75 bps back channel. Used in
the U.K.
V.25
An ITU-T standard for modem communications. Among other things, V.25 specifies an answer
tone different from the Bell answer tone. All U.S. Robotics modems can be set with the B0
command so that they use the V.25 2100 Hz tone when answering overseas calls.
V.25 bis
An ITU-T standard for synchronous communications between the mainframe or host and the
modem using the HDLC or character-oriented protocol. Modulation depends on the serial port
rate and setting of the transmitting clock source, &X.
V.27 terbo
An ITU-T standard for facsimile operations that specifies modulation at 4800 bps, with
fallback to 2400 bps.
V.29
An ITU-T standard for facsimile operations that specifies modulation at 9600 bps, with
fallback to 7200 bps.
V.32
An ITU-T standard for modem communications at 9600 bps and 4800 bps. V.32 modems fall back
to 4800 bps when line quality is impaired, and fall forward again to 9600 bps when line
quality improves.
V.32 bis
An ITU-T 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, and
fall back further as necessary. They fall forward to the next higher speed when line
quality improves.
V.32 terbo
Modulation scheme that extends the V.32 connection range: 4800, 7200, 9600, 12K, 14.4K,
16.8K, 19.2K, and 21.6K bps. V.32 terbo modems fall back to the next lower speed when line
quality is impaired, and fall back further as necessary. They fall forward to the next
higher speed when line quality improves.
V.34
An ITU-T standard that allows data rates as high as 28.8K bps. See V.8.
V.42
An ITU-T 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 4.
V.42 bis
An extension of ITU-T V.42 that defines a specific data compression scheme for use with
V.42 and MNP error control.
V.Fast Class (V.FC)
Proprietary modulation scheme developed by Rockwell International for data communication
speeds up to 28.8K bps.
VAC
Voltage, Alternating Current
W
WAN
Wide Area Network- A network that is not limited to a specific location. A WAN may link up
several LANs together as one network.
Word Length
The number of bits in a data character without parity, start or stop bits.
WORLD PORT
Portable fax and data modems that are designed for business people who travel.
X
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. Other related protocols are Ymodem and Zmodem.
XON/XOFF
Standard ASCII control characters used to tell an intelligent device to stop/resume
transmitting data. In most systems typing <Ctrl>-S sends the XOFF character. Some
devices, including the Courier, understand <Ctrl>-Q as XON; others interpret the
pressing of any key after <Ctrl>-S as XON.
Y
Z
X.75
X.75 defines the connection between public networks such as larger computers and
mainframes.
Xon/Xoff
Standard ASCII control characters used to tell an intelligent device to stop/resume
transmitting data.
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