                                                                 
                                            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 <Ctrl>-S sends the XOFF
      character.  Some devices, including the
      Sportster 14,400, understand <Ctrl>-Q as
      XON; others interpret the pressing of
      any key after <Ctrl>-S as XON.

