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    ANSWER MODE

        Used by the modem when answering a call from another computer. The
        modem uses "originate mode" when calling another computer. Although
        your modem can operate in either mode, some modems operate only in
        originate mode.  To communicate with these modems, your modem can
        switch to answer mode after placing (originating) a call.

        ASCII (American Standard Code for Information Interchange)
        A standard method of encoding characters that enables text generated by
        one program or computer to be understood by another program or
        computer.


    ASYNCHRONOUS COMMUNICATION

        Communication between computers at irregular intervals.  To handle this
        kind of communication, the modem adds start and stop bits to each
        character it sends.  The start bit lets the receiving computer know
        when a new character has started.  The stop bit indicates the end of
        the character.


    AT COMMAND SET

        The set of industry-standard commands used to control the modem. Each
        command line must start with the two-character attention code AT (or
        at).


    ATTENTION CODE

        The two-character sequence AT or at. Signals the modem that one or more
        modem commands are to follow.


    AUTOMATIC ANSWERING (OR AUTO ANSWER)

        The modem automatically answers the phone after a certain number of
        rings.  This is in contrast to manual answering, where a person sends
        an AT command to the modem to cause the modem to answer a ringing
        telephone.


    AUTOMATIC DIALING

        The modem automatically dials the telephone.  This is in contrast to
        manual dialing, where a person dials the number.



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    AUTO-RELIABLE MODE

        The modem automatically negotiates with the remote modem for a
        connection, determines whether or not it can use error control and data
        compression during a transmission, and determines which error control
        and data compression protocol it can use.


    BAUD RATE

        The number of symbols transmitted per second.  This is not always the
        same as the bps rate (see "Bits per second"), because a given symbol,
        or baud, may have more than one bit.


    BELL 103 AND 212A (AMERICAN BELL STANDARD)

        A North American standard that specifies the way modems transmit
        information.
        *   Version 103 applies to asynchronous modems transmitting at speeds
            up to 300 bps.
        *   Version 212A applies to full duplex asynchronous or synchronous
            modems that transmit at speeds up to 1200 bps.


    BITS PER SECOND (BPS)

        The speed at which a modem sends or receives information. For example,
        a modem that operates at 2400 bits per second can transfer 2400 binary
        digits each second.  A character normally consists of seven or eight of
        these binary digits, plus the start and stop bits that separate the
        character from other transmitted characters.


    BUFFER

        A storage location in its internal RAM where the modem can temporarily
        store data it receives until it can process the data.


    CARRIER

        The base signal used to transmit data across a telephone line. The
        modem modulates this signal (alters its frequency or phase) to encode
        the data to be transmitted.







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    CCITT

        (Consultative Committee for International Telephone and Telegraph)
        An international committee that specifies the way modems and fax
        machines transmit information to ensure compatibility among modems.
        (Note:  bis means the second version of a particular standard.)
        *   CCITT V.21 -- 300 bps modems
        *   CCITT V.22 -- 600 and 1200 bps modems
        *   CCITT V.22bis -- 2400 bps modems
        *   CCITT V.32 -- 4800 and 9600 bps modems
        *   CCITT V.32bis -- 4800, 7200, 9600, 12000, and 14400 bps modems
        *   CCITT V.42 -- error control
        *   CCITT V.42bis -- data compression
        *   CCITT V.54 -- testing


    CLEAR TO SEND (CTS)

        An RS-232C signal that tells the computer it can start sending
        information.  See also Request to send (RTS).


    COMMAND MODE

        One of the two operating modes of the modem, sometimes called local
        mode or terminal mode.  (The other is on-line mode.) In command mode,
        the modem interprets any information it receives from the local
        computer (or terminal) as modem commands.  It tries to perform the
        commands sent to it, and it returns result codes indicating the results
        of the commands.  The modem enters command mode when you turn on or
        reboot your computer (or terminal), or when you type the escape
        sequence (normally +++) while the modem is in on-line mode.


    COMMUNICATION (COM) PORTS

        The connectors and accompanying circuitry on your computer that let you
        connect serial devices (usually serial printers, modems, or mice) to
        your computer and communicate with these devices. Communication ports
        are also called serial ports.  To keep track of the devices, DOS
        assigns names that begin with the letters COM to communication ports
        (such as COM1 and COM2).


    COMMUNICATIONS SOFTWARE

        A program that sets up your modem and gives you a human interface to
        the various functions of your modem.  Examples of DOS-based
        communications programs are Smartcom, Procomm, and Crosstalk. Examples
        of communications programs for the Macintosh are Quick Link II,
        MicroPhone, and Red Ryder.

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    CONFIGURATION PROFILE

        The current operating characteristics of your modem, stored in the
        modem's S-registers.  Whenever you issue a modem command to change one
        of the operational characteristics (such as setting the volume control
        or turning the speaker on or off), the modem changes the values in the
        S-registers to reflect your changes.


    DATA CARRIER DETECT (DCD)

        An RS-232C signal that indicates the modem is receiving a carrier
        signal from a remote modem.


    DATA COMPRESSION

        The encoding of text or data so that it takes up less space (fewer
        bits).  CCITT V.42bis and MNP class 5 are two different data
        compression protocols.  Data compression allows your modem to transmit
        more information in a shorter period of time and thus increases your
        modem's data throughput.


    DATA SET READY (DSR)

        An RS-232C signal that tells the computer (or terminal) the modem is
        connected to the telephone line.


    DATA TERMINAL READY (DTR)

        An RS-232C signal that tells the modem the local computer (or terminal)
        is ready for data transmission.


    DIAL MODIFIERS

        AT commands that you enter along with the AT command D (dial) to
        further instruct the modem when dialing the telephone.  Dial modifiers
        specify things like whether to use pulse or tone dialing, when and how
        long to pause between numbers, and whether to dial a stored number.


    DUPLEX

        The way modems exchange data:  half duplex or full duplex.  With half
        duplex transmissions, only one modem can send data at a time.  Full
        duplex transmissions allow both modems to send data simultaneously.



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    ERROR CONTROL

        The encoding of text or data so that a receiving modem can detect and
        sometimes correct errors in data transmissions.  LAPM and MNP classes 1
        through 4 are two different error control protocols.


    ESCAPE SEQUENCE

        A sequence of three characters (normally +++) that switches the modem
        from the on-line mode to the command mode without breaking the
        telephone connection.


    FILE TRANSFER PROTOCOL

        An error-checking protocol for file transfers (such as KERMIT, XMODEM,
        or YMODEM).  It monitors information sent with each block of data.  If
        the received data doesn't match the information used to check the
        quality of data, the system notifies the sender that an error has
        occurred and asks for a retransmission.


    FLOW CONTROL

        The mechanism that regulates the flow of data between two devices.
        Modems typically have two methods of flow control software flow control
        (XON/XOFF) and hardware flow control (CTS/RTS).


    GUARD TIME

        A period of time during which the modem must not receive characters.
        The escape sequence (normally +++) has a guard time to ensure that data
        sent from a remote modem isn't interpreted as an escape sequence.  The
        factory setting for the guard time is one second.  For the modem to
        interpret an escape code as valid, there must be one second before and
        one second after the escape sequence in which the modem doesn't receive
        any characters.


    HAYES COMPATIBILITY

        Software (and people) communicate with modems using the AT command set
        originally developed by Hayes Corporation.  Modems that use the AT
        command set are said to be Hayes-compatible.


    HOOK FLASH

        The act of hanging up the telephone for a short period of time (one-
        half second).  This operation is useful in PBX systems that interpret a
        hook flash as a signal to perform other services, such as transferring
        a call.

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    LAPM (LINK ACCESS PROCEDURE FOR MODEMS)

        LAPM is an error control protocol specified by CCITT V.42.  LAPM
        provides error control when your modem is communicating with another
        modem that supports LAPM.


    LINE NOISE

        Random signal disturbances that sometimes occur over telephone lines.
        Noise can disrupt communications and corrupt the transmitted data.


    LOOPBACK TEST

        Diagnostic test where characters that are sent to the modem are
        immediately sent back from the modem so the computer can compare the
        characters sent with the characters received.


    MANUAL DIALING

        Dialing a remote modem from a telephone connected to the modem. This is
        in contrast to automatic dialing, where the modem dials the number.


    MNP (MICROCOM NETWORKING PROTOCOL)

        Provides error control and data compression when your modem is
        communicating with another modem that supports MNP.  (MNP classes 1
        through 4 are specified by CCITT V.42 as a backup error control scheme
        for LAPM.)  Your modem supports five MNP classes. Each MNP class has
        all the features of the previous class plus its own.

        *   MNP class 1 (also called block mode):  Sends data in one direction
            at a time.  About 70 percent as fast as data transmissions using no
            error correction.

        *   MNP class 2 (also called stream mode):  Sends data in both
            directions at the same time.  About 84 percent as fast as data
            transmissions using no error correction.

        *   MNP class 3:  Sending modem strips start and stop bits from data
            block before sending it.  Receiving modem adds start and stop bits
            before passing the data to the receiving computer. About 8 percent
            faster than data transmissions using no error correction.




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        *   MNP class 4:  Monitors the quality of the connection and
            streamlines the information in the headers of data blocks. If the
            telephone line is relatively noise-free, the modem sends larger
            blocks of data to increase throughput. If the telephone line is
            noisy, the modem sends smaller blocks of data so that less data
            will have to be resent. This means more successful transmissions on
            the first try. About 20 percent faster than data transmissions
            using no error correction.

        *   MNP class 5:  Provides data compression. Sending modem detects
            redundant data and recodes it to fewer bits to increase the
            effective throughput. Receiving modem decompresses the data before
            passing it to the receiving computer. Up to 100 percent faster than
            data transmissions using no data compression or error correction,
            depending on the kind of data transmitted. (Files that are already
            compressed will seem to contain less redundant data and may
            therefore take longer to transmit using MNP class 5 than they would
            if you were using no data compression.)


    MODEM (DERIVED FROM MODULATOR/DEMODULATOR)

        A modem transforms (modulates) digital information into an analog
        signal that can be sent across a telephone line. It also demodulates an
        analog signal it receives from the telephone line, converting the
        information contained in the signal back into digital information.


    NONVOLATILE MEMORY

        Memory that retains the information stored in it even if you turn off
        the computer.  There are two kinds: ROM and NVRAM.  ROM is programmed
        with information at the factory, and you can't change it.  NVRAM is
        used to store configuration information, and you can changed it with
        modem commands.


    NVRAM (NONVOLATILE RAM)

        See Nonvolatile memory.


    OFF-HOOK

        The condition of a telephone line that corresponds to picking up the
        telephone receiver.  A modem creates an off-hook condition when it
        tries to communicate on a telephone line.





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    ON-HOOK

        The condition of a telephone line that corresponds to hanging up the
        telephone receiver.  A modem creates an on-hook condition to break its
        connection to a telephone line.


    ON-LINE MODE

        One of the two operating modes of the modem, also called data mode.
        (The other is command mode.) In on-line mode, the modem interprets all
        information sent to it as data, not commands.  The only exception is
        the escape sequence (normally +++), which returns the modem to command
        mode without breaking the connection.  The modem is placed in on-line
        mode when it makes a connection with a remote modem, or when you enter
        the O command to return to a previously established connection.


    ORIGINATE MODE

        The mode used by the modem when calling another computer. See also
        "Answer mode."


    PARITY

        A data encoding scheme that computers (and terminals) use to check the
        validity of transmitted characters.  This scheme adds an extra bit to
        each character, which the transmitting computer sets or clears based on
        the type of parity the computers agree to use (odd or even).  For
        example, if the computers use even parity, the transmitting computer
        sets or clears the parity bit so that there are an even number of bits
        set in each character it transmits.  The receiving computer checks each
        character and flags a parity error if any character has an odd number
        of bits set.


    PROTOCOL

        A set of rules that governs how data is transmitted.  To communicate
        successfully, two computers must use the same protocol.


    PULSE DIALING

        A method of dialing the telephone where the modem sends pulses (which
        you hear through the handset as clicks) to represent the telephone
        numbers (one pulse for a one, two pulses for a two, etc.). Pulse
        dialing is normally associated with rotary-dial phones. See also "tone
        dialing."


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    RELIABLE CONNECTION

        A connection between two modems where they communicate using an error
        control protocol (such as LAPM or MNP).


    REQUEST TO SEND (RTS)

        An RS-232C signal that requests the modem to send data. It initiates
        any data transmission between the computer (or terminal) and the modem.
        It is answered by a Clear to send (CTS) signal.  See also "Clear to
        send."


    RESULT CODES

        When you enter most modem commands, the modem displays a message on
        your screen, called a result code, that tells you the results of the
        command. In the factory setting, result codes are returned as English
        words that describe the conditions.  You can also set the modem to
        display corresponding numbers instead of words.


    RS-232C

        A standardized connection system for connecting a device to the serial
        port of a computer or terminal.  This is the recommended standard of
        the Electronic Industries Association (EIA) for exchanging information
        between Data Terminal Equipment (such as computers) and Data
        Communications Equipment (such as modems).


    S-REGISTERS

        RAM in your modem that is used to store the current configuration
        profile (operating characteristics) of your modem.


    SERIAL PORT

        The circuits and connector that let your computer communicate with
        serial devices such as printers, modems, plotters, mice, and custom
        laboratory equipment.  (Also called a COM or communications port.)


    SOFTWARE FLOW CONTROL

        See XON/XOFF.




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    START/STOP BITS

        The bits at the beginning and end of a data block when using
        asynchronous data transmission.  See also "Asynchronous Data
        Transmission."


    THROUGHPUT

        The total useful information processed or communicated in a specified
        amount of time.  Data compression increases the throughput of your
        modem by allowing you to send more information in the same number of
        bits.


    TONE DIALING

        One of two methods of dialing the telephone.  (The other is pulse
        dialing.)  With tone dialing, the modem sends tones of different
        frequencies to represent the telephone numbers.  Tone dialing is
        normally associated with push-button (touch-tone) phones and is also
        called Dual Tone Multi-Frequency (DTMF) dialing.


    V.21, V.22, V.22BIS, V.32, V.32BIS, V.42, V.42BIS, V.54

        CCITT specifications for modems.  For details, see "CCITT."


    XON/XOFF

        A way of controlling the flow of data between a modem and its host
        computer and between two modems, also called software flow control.
        XON stands for "Transmitter On," and XOFF stands for "Transmitter Off."
        If the modem receiving data needs time to process the data or do some
        other task, it sends an XOFF signal to the host computer (or sending
        modem).  The host computer (or sending modem) then waits until it
        receives an XON signal before sending more data.














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