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A networking standard that utilizes UTP cabling with RJ-45 connectors, and transfers data at up to 10 Mbps. It has the advantage of utilizing economical and easy-to-install cabling.

A networking standard that transfers data at up to an amazing 100 Mbps, and utilizes UTP cabling with RJ-45 connectors.

Original Ethernet using coaxial cable.

A networking standard that utilizes thin coaxial cabling with BNC connectors, and transfers data at up to 10 Mbps. It has the advantage of utilizing cabling with longer maximum lengths (610.5" as opposed to 330" with 10BaseT cabling).

A technology that allows a serial port to transmit compressed data at up to 115.2 Kbps.

A technology that allows a serial port to transmit compressed data at up to 460.8 Kbps.

Defined by the IEEE (Institute of Electrical and Electronics Engineers), these standards regulate the use of the CSMA/CD (Carrier Sense Multiple Access/Collision Detection network access method used by Ethernet networks.

The number of bits which represent each pixel, or point on the screen. An 8-bit per pixel card can generate 256 colors; 24 bits per pixel yields 16.8 million colors.

An IBM color monitor capable of resolutions of 720x400 non-interlaced with a refresh rate of 70MHz; 640x480 non-interlaced at 60MHz; or 1024x768 interlaced at 43.58 MHz. All of these resolutions are in 256 colors.


A formula or procedure which employs various methods defining how data is to be used to give a prescribed result.

The variation in a sound signal producing varying levels of loudness. Measured in decibels (dB).

Analog Signals
Signals which can vary over a continuous range (e.g., the human voice over conventional telephone lines). Analog circuitry is more subject to distortion and noise, but it is more capable of handling complex signals than are digital signals which can have only discrete values.

Analog Sound
Recorded sound depicted by fluctuations in amplitude.

Automatic ReQuest for retransmission. A type of communications link where the receiver asks the transmitter to re-send a block of data when errors are detected.

American National Standards Institute. A non-profit, private industry association which governs most USA-standards setting agencies.

Acronym for American Standard Code for Information Interchange. ASCII is an ANSI character set. The standard ASCII character set consists of 128 decimal numbers (0-127) for letters of the alphabet, numerals, punctuation marks, and common special characters. The extended ASCII character set extends to 255 characters and contains special mathematical, graphics, and foreign characters.

Asynchronous Communications
A method of transmission in which one character is sent one bit at a time; also referred to as serial transmission.

AUI connector
A networking connector that can be used with a transceiver to connect various kinds of cables such as fiber optic (10BaseF), thick coaxial (10Base5), thin coaxial (10Base2) and UTP (10BaseT).

auto-switching power supply
An electrical plug that will work internationally in 110-, 220- or 230-volt outlets by automatically detecting the current and using the appropriate voltage.


Bell standards
Refers to the U. S. modulation protocol standards developed by the former AT&T Bell Systems such as Bell 103 (300bps transmission) and Bell 212A (1200bps transmission).

Basic Input Output System. Provides fundamental services required for the operation of a computer. Permanently present in the machine, these routines are generally stored in ROM (Read Only Memory). The system board contains a ROM BIOS to support all of its standard functions. The Voyager Movie Player also has a BIOS for display features.

Bit Block Transfer
A method of holding a block of graphics, such as Windows dialogue box, in memory so that it can be moved and redrawn quickly by memory-to-memory operations.

Bit-mapped Registers
An S-register which contains multiple bit-oriented values.

Blind Dialing
An automated process whereby the modem goes off-hook and dials without waiting for a dial tone. This is prohibited in many countries.

Block Transfer Control
Determines whether or not the modem uses block or stream mode during an MNP connection. In stream mode, MNP sends data frames in varying length. Block mode sends fixed data frames of 256 characters.

BNC connector
A connector utilized in 10Base2 networks with thin coaxial cabling.

(Boot Programmable Read-Only Memory). A ROM chip usually mounted on the network interface card that enables a personal computer to load the operating system from the network.

Bits per second.

Break Handling
Determines how the modem responds when a BREAK signal is received from either the DTE (Data Terminal Equipment or computer/terminal) or the remote modem. This is controlled by the MNP-based AT extended commands. A break signal is represented on the communications line by a steady space signal for a significant length of time. Break signals may be activated from the keyboard by pressing the BREAK key or the control (CTRL) and C keys.

Bus topology
A network topology in which nodes are connected to a single cable with terminators at each end.


Consultative Committee for International Telephone and Telegraph. This advisory organization is part of the ITU (International Telecommunication Union) which is an agency of the United Nations. Organization recently renamed International Telecommunications Union-Telecommunications Standard Sector (ITU-T)

CD Quality
Recording quality similar to that of a compact disc player. This means that 16 bits of information are recorded for every sample taken. See Bits Per Sample and Sampling.

Color Graphics Adapter. Medium resolution IBM graphics standard capable of displaying 640 x 200 pixels in 2 colors, or 320 x 200 pixels in 4 colors.

Coaxial Cable
Data transmission medium with a single-wire conductor insulated from electro-magnetic and radio frequency interference.

Command Mode
The modem is in command mode when it is turned on or reset, when it loses its connection to a remote modem, when it is in on-line mode, or when escape characters (+++) are typed. To transmit data, the modem must be in data mode. The modem does not transmit data when in command mode.

Communications Protocol
A set of procedures which controls how a data communications network operates.

See hub.

Carrier Sense Multiple Access with Collision Detection. CSMA/CD is the access method used in Ethernet where nodes contend for the right to send data.


Data Carrier Detect. Indicates to the terminal device that the modem is receiving a valid carrier signal from a remote modem. The carrier is a tone at a specified frequency.

Data Communications Equipment. The local and/or remote modem. A DCE is usually connected to a DTE.

Direct Memory Access. DACK stands for Dma ACKnowledge and DRQ for Dma ReQuest. DMA provides direct access to system memory without adding to CPU overhead. The DACK and DRQ channels govern that communication.

Data Terminal Equipment. The computer or terminal, either local (yours), or the remote (the one you're communicating with). A DTE is usually connected to a DCE.

Dynamic RAM. RAM is random access memory.

Data Terminal Ready. The computer issues this signal to the attached modem indicating that it is ready to receive data.

Data Compression
A technique that examines transmitted data for redundancy and replaces strings (groups) of characters with special codes which the receiving modem interprets and restores to its original form. Transmission of compressed data results in shorter connect times and hence cost savings for connect charges. Data compression is sometimes called "source encoding".

Data Mode
The modem is in data mode when a connection has been established with a remote modem and sends a CONNECT response confirming the connection. User data may then be transmitted or received.

Decibel (dB)
A means of measuring amplitude.

Dial Modifier
Dial modifiers are special characters appended to the ATD command which instruct the modem how to place a call.

Digital Signal
A discrete signal which can only take on one of several (usually only two) discrete levels in contrast to analog signals which can take a continuous range of levels.

Digital Sound
Recorded and stored sound as a series of numerical values rather than fluctuations in amplitude.

dual-line modem
A modem with two 56K modem chips on a single board that connects to two regular phone lines and utilizes bonding software to offer transmission speeds of up to 112 Kbps.


Enhanced Color Display. An EGA specification. TTL monitor capable of displaying video signals with horizontal scan frequencies of 15.750KHz (CGA) or 21.850KHz (EGA) only.

Enhanced Graphics Adapter. High resolution IBM graphics standard capable of displaying 640 x 350 pixels in 16 colors out of a palette of 64 colors.

Error Detection and Correction.
The transmitting modem attaches a special pattern (called a frame check sequence) calculated according to a prescribed algorithm from user-defined data to the end of a block of data. The receiving modem performs the same algorithm and compares it to the one with the transmitted data. If these match, then the block of data has been received correctly. If not, the block of data is re-transmitted until no errors are detected.

Escape Sequence
Also referred to as the escape command. This special command is entered as three plus symbols (+++) and places the modem in command mode and interrupts user data transmission, but does not terminate the data connection. This allows the entering of commands while the connection is maintained.

A 10 megabits-per-second baseband, CSMA/CD network originally designed by the Xerox Corporation.

Extended AT-Command
Extended commands were developed to provide greater functionality and control over modem operations than is available from the basic AT command set.


Fax Mode
The modem is in fax mode when, through use of fax communications software, it can send and receive faxes, print and display fax files, convert files to fax-files, and set certain fax-related features. Note: the modulation protocol used by the modem in fax mode is also different from the usual data mode modulation.

Feature Connector
Used by graphics adapters to give compatibility with VGA text and graphics codes for use with multi-media applications.

File Server
A device on a LAN that provides mass storage of files. A file server can be dedicated (only performs network management functions) or non-dedicated (where user applications can co-exist while the network is available.

Flow Control
Compensates for the difference between the rate at which data reaches a device and the rate at which the device processes and transmits. The two common types of flow control are RTS/CTS signaling (a hardware based method, employing an electrical signal) and XON/XOFF (a software-based method using standard ASCII control characters to pause or resume transmission). The \G command controls XON/XOFF flow control.

full duplex
The ability to send and receive data at the same time. (A full duplex speakerphone allows you to hear what is going on at the other end of the line while you are talking.)


Guard Tone
Guard tones are used in the United Kingdom and other countries. This requires that the modem transmit an 1800-Hz tone after it sends an answer tone. The guard tone is controlled by the &G command. Guard tones are not used in the U.S.A.

Graphical User Interface.


half duplex
The ability to send data in only one direction at a time.

Hayes Microcomputer Products, Inc. developed the AT command set which has become a de facto industry standard. Hayes commands are always initiated with an AT (attention code) prefix.

Hardware Graphics Cursor
Provides a faster method of displaying/moving a cursor (GUI arrow) on the screen. The video adapter's main chipset controls this function which resides in system memory, as opposed to slower handling by the application software.

Hercules Graphics Card. Compatible with MDA, but also capable of displaying 720 x 348 pixels in a 4-bank graphics mode.

Short for High Resolution, this term should be only applied to a minimum of 640 x 350 resolution and above.

Hook Flash
The dial modifier "!" causes the modem to go on-hook (hang-up) for one-half second. Also controlled by the ATH command.

Horizontal Scan Rate
The frequency in KHz (kilohertz) at which the monitor is scanned in a horizontal direction; high horizontal scan rates produce higher resolution. The EGA horizontal scan rate is 21.8 KHz, while the extended EGA horizontal scan rate is 30.1 KHz.

A networking device with multiple ports that allows you to connect workstations, servers or peripherals to a network.


IEEE 802.3 compliant
Complying to the standards for 10 Mbps networks established by the Institute of Electrical and Electronic Engineers (IEEE)

A method of scanning a screen which results in alternate lines being drawn with each full pass of the electron beam. The resulting display is less stable than a flicker-free non-interlaced display.

I/O card
An abbreviation for input/output card. A board in your PC with a serial or parallel port that allows you to connect peripherals to your computer. I/O cards can also have multiple serial or parallel ports or a combination of both.


This occurs when there are excessively long data packets being transmitted from the node (i.e., workstation, server). At that point, the hub, or concentrator, partitions (isolates) the node from the network until the condition is corrected.

jabber protection
A feature of some networking hubs that ensures your network won't go down due to excessively long data packets.

A set of tiny switches used to select one of various options such as a particular hardware configuration.


An abbreviation for kilobits per second. A measurement of the transmission speed of data measured in 1,024 bits per second.


(Local Area Network) A data communications network confined to a limited geographic area, with moderate to high data rates (100kbps to 100Mbps). The area served may consist of a single building or campus-type arrangement. It is owned by it's use, includes some type of switching technology, and does not use common carrier circuits - although it may have gateways or bridges to other public or private networks.

Link Access Protocol Modem. A V.42 ARQ type of error correction protocol where LAPM may be activated with or without V.42bis data compression.

Leased Line
Also referred to as a private line. A leased line is obtained from a communications company (carrier) to provide a transmission medium between two points. The line consists of a permanent dedicated circuit between two points, or to set of previously arranged points. The cost of the line is usually based on the distance between locations. This is in contrast to switched or dial-up lines, which can be connected to any point on the network.

Light-emitting diode.

Line Modulation
The means by which a carrier is varied to represent a signal carrying information. In a modem, the user's digital data is used to modulate the modem's transmitter's carrier or carrier to allow the digital signal to be carried over analog facilities.

A connector on audio equipment to which a device like a CD-player or tape cassette player may be attached. See also Line Out.

A connector on audio equipment to which audio components can be attached such as stereo speakers. See also Line In.

Long Space Disconnect
Determines whether or not modem disconnects when it receives a continuous break from a remote modem. Controlled by the ATY command.

Loopback Tests
There are four types of loopback tests which are as follows: (1) the local digital loopback tests the operation of the DTE, including whether or not data is leaving the terminal or computer port; (2) the local analog loopback tests the digital and analog circuits of the modem; (3) the remote digital loopback checks the operating condition of the line and remote modem; (4) the remote analog loopback tests the line to the remote modem.


Make/Break Ratio
The &P command controls the ratio of the off-hook (make) to on-hook (break) interval used by the modem when it pulse dials. &P0 selects a 39%/61% make/break ratio for use in the U.S. &P1 selects a 33%/67% make/break ratio for use in the United Kingdom and Hong Kong. The &P command is NOT allowed in some countries.

Monochrome Display Adapter. Early IBM Video display board designed for use with IBM monochrome text standard.

Musical Instrument Digital Interface. A standard which allows for the exchange of data between two music synthesizers or a synthesizer and a computer. Sound data may be communicated from the synthesizer to the computer and stored as a MIDI file. Or, a MIDI file can be transmitted to the synthesizer for playback.

Microcom Networking Protocol. A series of data communications protocols developed by Microcom for full-duplex, error-free communications.

Modulation Handshake
Also referred to as Automode Enable and is controlled by the ATN command. This determines whether or not the modem must connect at a particular speed, or allow connection at any speed supported by both modems.

A UART on the MIDI port which allows MIDI interface to transmit and receive at 32.5K baud (see Appendix E for more information).

(Motion Pictures Expert Group). A type of data compression storage and playback of video and audio data.

An abbreviation for megabits per second. A measurement of the transmission speed of data measured in 1,048,576 bits per second.

Multiple Frequency Monitor
Monitor capable of displaying video signals over a wide range of horizontal scan frequencies. This may include a horizontal capture range from 5.5KHz to 35KHz or wider. Examples of monitors in this class are the NEC MultiSync and the Sony Multiscan. The Multiscan has a wide horizontal scan capture range which enables it to display monochrome signals.


Negotiation Fallback
Controlled by S-Register 36 as part of the V.42 protocol. Setting this register indicates what action to take when a desired connection cannot be made (e.g., hang-up, direct mode connect, normal mode connect).

network adapter card
A board in your PC that has one or more ports for connection to a network.

Network topology
The arrangement of nodes usually forming a star, ring, tree, or bus pattern.

Any device including servers and workstations connected to a network; also the point where devices are connected.

Non-Volatile RAM
Also NVRAM. Random access memory whose data is retained when power is turned off. This is especially useful for modems to store user-defined default configuration settings and frequently used telephone numbers. This information would be loaded into modem RAM at power-up.


On-Line State
Same as data mode. To transmit or receive data, the modem must be in the on-line state. When placing a call, the modem is put on-line with the dial command.


A collection of bits comprising data and control information formatted for transmission from one node to another.

The range of colors from which you can select the actual colors that the video adapter will display simultaneously.

parallel port
One of several kinds of connectors found on the back of computers used to connect peripherals. Peripherals that connect to parallel ports include printers, Zip drives, tape drives and CD-ROM drives.

Private Branch Exchange. A telephone switch at a customer site.

A sound's tone, usually determined by the sound's frequency

A single dot on the CRT display. This word is derived from the words 'picture' and 'element'.

Plug and Play
An industry-wide standard for add-on hardware which indicates that it will configure itself, thus eliminating the need to set jumpers, and making installation of the product quick and easy.

A standardized set of rules that specify the format, timing, sequencing, and/or error checking for data transmissions.

Pulse Dialing
Also referred to as rotary dialing, i.e., dialing with the older-style rotary dial wheel. The dial modifier ATDP sets the modem to pulse dialing, which is the default method as opposed to tone dialing (push-button touch-tone) which is enabled with ATDT. All telephone exchanges will accept older-style pulse dialing and most exchanges will accept modern tone-dialing. Tone dialing is faster and more reliable since mechanical relays and their inherent failure mechanisms are avoided.



RAM Digital to Analog Converter.

Refresh Rate
Also called Vertical Scan Rate, the speed at which the screen is repainted. Typically, color displays must be refreshed at 60 times per second. Usually, the faster the refresh rate, the less flicker a monitor has (normally defined in Hz).

Register Level Compatibility
Complete compatibility to the hardware level.

Used to extend the topology, allowing two or more cable segments to be joined. In a 10Base-T network, the repeater provides the central connection point where the gathering of statistics and network management functions take place.

Result Code
A response sent by the modem after executing a command. The response reports the modem's status or the progress of a call and can take the form of either digits (numeric) or words (verbose). Issuing a V1 command enables word responses. A V0 (V-zero) command enables numeric responses. The Q1 command disables their use entirely. Example: "OK" (word), or 0 (numeric) indicates that the modem successfully executed a command.

An adjustment process performed when one of the modems detects signal distortion or line noise which threaten data integrity.

RGB Monitor
Red/Green/Blue. A CGA compatible monitor limited to a 15.750KHz horizontal scan rate.

Ring Topology
A network topology in which nodes are connected in a closed loop; no terminators are required because there are no unconnected ends.

RJ-45 connector
A connector utilized in 10BaseT and 100BaseTX networks with UTP cabling.

Request to Send/Clear to Send. RTS and CTS are two control signal lines between the modem (DCE) and terminal (DTE) which allow the terminal to control the flow of information. See also flow control.


A measurement of sound taken during a certain duration. In digital recording, sampling means recording voltages which make a sound as a sequence of numerical values representing the sound's amplitude.

Scan Rate
The frequency in Hertz (Hz) at which the monitor is scanned horizontally. Generally, the higher the scan rate, the higher the resolution.

serial port
One of several kinds of connectors found on the back of computers used to connect peripherals. Peripherals that connect to serial ports include external modems, ISDN terminal adapters and mice.

A computer that provides shared resources, such as files and printers, to the network.

Sleep Inactivity Timer
Determines the length of time the modem operates in normal mode with no activity before entering low-power "sleep" mode.

software configurable
The ability of an add-on product to be configured by its software, thus eliminating the need to set jumpers, and making installation of the product quick and easy.

Sound File
Any file which holds sound data. Examples: files with .MID file name extensions are compatible with the MIDI standard (see above); a file with a .WAV file name extension is a standard Microsoft file format for storing waveform audio data. See Waveform and wave file.

Split-Speed Direction
Determines which direction (transmit or receive) has the 75bps channel and which has the 1200bps channel.

Standard AT-Command
The basic AT command set, originated by Hayes Microcomputer Products, Inc.

Star Topology
A network topology in which nodes are connected to a common device such as hub or concentrator.

Synchronous Communications
A method of transmission in which data bits are sent continuously at the same rate under the control of a fixed frequency clock signal.


A T-shaped device with two female and one male BNC connectors.

50-ohm coaxial plug used to attach to one end of a BNC T-connector when the associated station is first or last in the group.

thin coaxial cable
A networking cable with BNC terminators used on 10Base2 networks.

How the ear identifies and classifies sound. Example: the timbre of the same note played by two different instruments (flute and tuba) will not be the same.

Touch-Tone Dialing
Push-button tone dialing as used on contemporary phone sets. The dial modifier ATDT sets the modem to "tone" mode. Tone dialing is faster and more reliable than older-style pulse dialing.

The physical layout of a network. The principal LAN topologies are bus, ring, and star.

An AUI (Attachment Unit Interface) device for receiving and transmitting data that often provides collision detection as well.

Trellis Coding
A method of modulation which targets specific modulation points. Signals falling outside of these points are treated as line noise, thus ensuring greater noise immunity over a given line. QAM (Quadrature Amplitude Modulation) functions similarly, but has a broader tolerance and results in lesser noise immunity than trellis coding.

Terminate and Stay Resident. A program that remains in memory after it has been loaded.

Transistor-Transistor Logic; a fast, reasonable-cost type of integrated circuit used in some monitors.

TTL Monitor
Video and synchronization signals (all digital) are on separate lines and have TTL compatible voltage levels

Twisted-Pair cable
A wiring scheme with one or more pairs of 18 to 24- gauge copper strands.


UTP cable
An abbreviation for unshielded twisted-pair cable. A networking cable with RJ-45 connectors used on 10BaseT and 100BaseTX networks.


Video Electronics Standards Association.

(Video Graphics Array) Analog graphics standard introduced with the IBM PS/2 series. Backwards compatible with EGA at the BIOS level, but provides higher resolutions. Supports a maximum resolution of 640 x 480 pixels in 16 colors out of a palette of 262,144 colors.

Voice Annotation
Embedding of a voice message into a document for later playback.

A modem standard established by the ITU which assures that 56K modems that comply with the standard will be able to communicate with one another regardless of the manufacturer of the modem.


(Wide-Area Network) A network which uses common carrier-provided lines; contrast with LAN.

Wave File
A standard Microsoft file format for storing waveform audio data.

A graph showing the amplitude of a sound over a particular interval of time. Any portion of that interval is a sample.


XON and XOFF are the names of two different flow control characters. See also flow control.