DUPLEX - Indicates a communications channel that is capable of carrying   
   signals in both directions.   
      
      FULL-DUPLEX - Signal flow in both directions at the same time.   
      
      HALF-DUPLEX - Signal flow in both directions, but in only one   
      direction at a time.   
      
        SYMMETRICAL/ASYMMETRICAL - Describes whether    data flow in a   
        communications channel is balanced or unbalanced (ie. data flow   
        rate is the same in both channels or different).   
      
         Eg. The USR 16.8K HST protocol is full-duplex asymmetrical, it   
             employs one 16800bps channel and a second 450bps channel.   
             ITU-T V.32bis is full-duplex symmetrical, both channels   
             operate at 14400bps.   
      
   ENCODING - The process of impressing data onto a carrier. By varying the   
   frequency, amplitude, and phase of the data carrier, it is possible to   
   generate signals which are equivalent to one or more data bits per change   
   of state. Devices which operate above 300bps employ modulation technology   
   which encodes more than one bit per transition. 1200 and 2400bps modems   
   operate at 600 symbols/sec using data encoding techniques that yield 2 and   
   4 bits per symbol element respectively. Similarly, 9600 and 14400bps modems   
   operate at 2400 symbols/sec using techniques which yield 4 and 6 bits per   
   symbol element.   
      
   ERROR-CORRECTING MODEM - describes a modem which incorporates data   
   integrity checking protocols in its hardware (eg. MNP4 or V.42 capable   
   modems). When two such modems connect, they transmit data synchronously,   
   obviating the necessity of framing start and stop bits for transmitted   
   data; such modems are thereby able to achieve a 25 per cent increase in   
   throughput relative to non-error-correcting modems.   
      
   ESCAPE SEQUENCE - A command sent to a modem that will place it in command   
   mode.   
      
   EXPRESS-96 - A proprietary high-speed modulation protocol developed by   
   Hayes.   
      
   FLOW CONTROL -  A mechanism for compensating for differences in the flow of   
   data input to and output from a a modem.   
      
   FOSSIL - (F)ido-(O)pus-(S)eadog-(S)tandard-(I)nterface-(L)ayer. A   
   specification detailing the interface between a communications application   
   and a PC's serial communications hardware. Originally conceived to allow   
   programmers to implement common low-level serial I/O functions for their   
   applications on platforms that were not 100% compatible.   
      
   FSK - [F]requency [S]hift [K]eying. FSK describes the modulation of a   
   carrier (or two carriers) by using a different frequency for a 1 or 0. The   
   resultant modulated signal may be regarded as the sum of two amplitude   
   modulated signals of different carrier frequency.   
      
   GROUP - the standards that govern the way fax devices communicate with each   
   other across the phone line. Group 3 is defined in ITU-T Recommendations   
   T.4 and T.30, and is the set of capabilities implemented in the vast   
   majority of present fax devices that operate on analog telephone lines   
   (although some recent additions will also permit Group 3 protocols to be   
   used over digital circuits such as ISDN).   
      
   GSTN - The (G)eneral (S)witched (T)elephone (N)etwork, also referred to as   
   the (P)ublic (S)witched (T)elephone (N)etwork. The PSTN is, by definition,   
   the analog telephone network that provides voice and data access around the   
   world. Digital signals can also be sent after being modulated and sent as   
   an analog signal. When received, the analog signals are then demodulated   
   back into digital signals. This modulation/demodulation by a modem is   
   necessary, as dial-up PSTN lines are not as suitable for digital   
   communications as for voice communications. In actuality, this analog   
   telephone network is now mostly digital, except for the lines from the end   
   offices to the telephone or modem. However, since the connections at both   
   ends are analog, the PSTN can be considered to be essentially analog in   
   nature.   
      
   "HAYES COMPATIBLE" - A term that implies that a modem implements the   
   [AT]tention command set first utilized on the Hayes Smartmodem 1200.   
   Standardized as EIA602, but varies between manufacturers.   
      
       Basic "AT" Commands:   
      
       ATA - force answer mode   
      
       ATB - select Bell or CCITT modes (all but obsolete now)   
             B or B0 = CCITT   
             B1 = Bell   
      
       ATD - dial - see your manual for details as this is a flexible and   
             powerful command with lots of neat options.   
      
       ATE - echo on/off - echo is the copying of a command from the   
             terminal or computer back to it   
             E1 = on   
             E0 = off   
      
       ATH - hook status, ie. line state   
             H1 = off hook   
             H0 = on-hook   
      
       ATI - product code or identity code, some manufacturers put in   
             options to provide more or less information about the modem   
             being interrogated, for example:   
             I or I0 = ID and version number   
             I1 = checksum of EPROM   
             I2 = OK or ERROR on validity of checksum   
      
       ATL - speaker volume   
              L0 = low volume   
              L1 = medium volume   
              L2 = high volume   
      
       ATM - speaker function   
              M or M0 = speaker off   
              M1 = speaker on until carrier detected (normal)   
              M2 = speaker on while modem on line   
      
       ATO - originate - force originate mode or resume data state when on   
             line.   
      
       ATQ - result code output   
             Q or Q0 - normal result codes sent to terminal   
             Q1 - result codes not returned to terminal   
      
       ATS - set or read S register - see below   
      
       ATV - result code format output   
             V or V0 - single digit result codes generally most suitable   
             for a computer to interpret   
             V1 - "English" result codes suitable for human interpretation   
      
      
   --- MPost/2 v2.0a   
    * Origin: Marsh BBS (c) Dawson Creek BC Canada (1:17/23)