Software Vault: The Gold Collection

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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.