constellation offers higher encoding density with its "quintbits" (2=32),  
  as opposed to the 16-point constellation with its "quadbit" structure  
  (2=16).  
    
  With a given fixed symbol rate (e.g., 2400), the 16-point constellation can  
  deliver data exchange rates of 9600 bps (2400X4). The more-complicated  
  32-bit constellation offers an intrinsically higher data rate capacity of  
  12,000 bps (2400 symbols/sec X 5).  It's also more susceptible to channel  
  noise because you have to push the individual decision points closer  
  together, and any minor noise perturbation is more likely to cause the  
  distant receiver to make a decoding error.  
    
  However, instead of using the higher density of the 32-point constellation  
  for speed purposes, suppose you use its added complexity for noise immunity  
  purposes to derive a performance boost.  TCM does just that.  
    
  Instead of operating at 12,000 bps, V.32 TCM transmission remains at 9600  
  bps with twice as many constellation points as it needs.  The extra  
  constellation bits produce a redundant bit.  This fifth bit is used as an  
  embedded "checksum" to produce intelligent transmission. Decision rules are  
  used in both the transmitter and the receiver to produce an orderly  
  transmission that is designed to maximize noise immunity.  
    
  The redundant bit serves an error-detection function similar to the ninth  
  bit used for parity in 8-bit PC memory systems.  The memory bit doesn't  
  prevent errors from occurring; however, it flags them and prevents them  
  from propagating.  
    
  With TCM, the fifth bit acts to help the remote receiver make a high-  
  probability choice among possible alternatives when  channel noise has  
  distorted the incoming signal.  It doesn't absolutely guarantee error free  
  communication, but helps reduce the probability of errors. The net result  
  is about 4 decibels (a little more than double) the S/N ratio of a non  
  encoded system.  
    
  TSB38/37A - A network model description and set of testing procedures which  
  are defined in Technical Standard Bulletins of the Telecommunications  
  Industry Association. The TSB37A test suite is used with modem performance  
  test procedures given in TSB38.  It is widely used today for comparisons  
  between modems. It models the network as two independent local loops with a  
  four-wire trunk connection between them.  Impairments primarily found in  
  the digital network are specified in proportion to their believed presence  
  in the network.   For instance, up to three PCM links are included in the  
  tests. ADPCM is also represented.  
    
  There are also minimal tests that represent the older analog equipment in  
  the network. Each loop and trunk connection specified is assigned a  
  Likelihood of Occurrence percentage (LOO).  By multiplying the scores for  
  the loop combination and the trunk, an overall LOO can be assigned to a  
  given test.  A LOO of 4% indicates that the results of that test represent  
  4% of the expected connections in the actual network.  
    
  UART - (U)niversal (A)synchronous (R)eceiver (T)ransmitter - a  
  semiconductor which interfaces serial ports to the processor buss.  
    
      FIFO - (F)irst-(I)n-(F)irst-(O)ut - describes the data handling  
      technique utilized by high-performance buffered UARTs such as the  
      NS16550AFN.  
    
  V.8 - Procedures for starting sessions of data transmission over the  
  general switched telephone network  
    
  V.17 - ITU-T recommendation of Facsimile operation at up to 14400bps.  
    
  V.18 - Operational and inter-working requirements for modems operating in  
  the text telephone mode  
    
  V.21 - ITU-T recommendation for modem communications at 300bps. NOTE: this  
  recommendation is widely utilized outside of the United States and Canada  
  where the Bell 103 protocol is more prevalent.  
    
  V.22 - ITU-T recommendation  for modem communications at 1200bps. NOTE:  
  This recommendation is compatible with the Bell 212A protocol which is  
  prevalent in the US and Canada for devices which operate at 1200bps.  
    
  V.22bis - ITU-T recommendation for modem communications at 2400bps.  
  Includes an automatic link negotiation fall-back to 1200bps and  
  compatibility with Bell 212A/V.22 modems.  
    
  V.25 - ITU-T recommendation which specifies a 2100Hz answer tone which is  
  different from the Bell answer tone used in the US and Canada.  
    
  V.25bis - ITU-T recommended command language for modems.  
    
  V.27ter - ITU-T modulation scheme used in Group 3 Facsimile for image  
  transfer at 2400 and 4800 bps. It is also used for 4-wire leased line  
  modems.  
    
  V.29 - ITU-T modulation scheme used in Group 3 Facsimile for image transfer  
  over dial-up lines at 9600 and 7200 bps.  
    
  V.32 - ITU-T recommendation for modem communications at 9600 and 4800bps.  
  Incorporates fall-back/fall-forward logic for operation on impaired phone  
  lines.  
    
  V.32bis - ITU-T recommendation which extends the V.32 connection range to  
  incorporate link rates of 4800, 7200, 9600, 12000, and 14400bps.  
  Incorporates logic that falls back to the next lower speed when line  
  quality deteriorates, and fall back further as necessary. Also incorporates  
  fall forward and rapid rate negotiation logic.  
    
  V.32terbo - 19200bps, with fall back to 16800bps. Designed by AT&T, and is  
  public domain, so any manufacturer can use this standard and put it into  
  their modems. USR has further extended this to support a proprietary link  
  rate of 21600bps.  
    
  V.32turbo - A modulation protocol developed by Rockwell which extended V.32  
  link rates to 12000bps.  
    
  V.34 - ITU-T recommendation for data signalling rates of up to 33.6kbps for  
  use on the general switched telephone network and on leased point-to-point  
  2-wire telephone-type circuits.  
    
  V.42 - ITU-T recommendation for modem communications that defines a  
    
  --- MPost/2 v2.0a  
   * Origin: Marsh BBS (c) Dawson Creek BC Canada (1:17/23)