Shareware Grab Bag/Shareware Grab Bag.iso/007/tbullets.arc/QBLT9

Text File | 1987-11-10 | 2KB | 35 lines

   WHAT IS AN "ERROR-CORRECTING MODEM?"

   Error-correcting modems perform error correction and recovery on
   incoming data by themselves.  This is a feature usually implemented
   in the modem's internal firmware (ROM, for example).  The accepted
   standard for internal modem error correction is MNP (Microcom
   Networking Protocol), names after the company (Microcom) who
   developed it.  MNP is not a "Fixed" standard, it is available in
   levels 1 thru 6, with MNP level 3 being the most commonly available
   implementation.

   For two modems to establish an error-free connection, they must
   both support the same MNP level.  Higher levels of MNP, however,
   are compatible with lower levels of the standard.  Two modems
   supporting MNP level 3 and communicating at 2400 (using the Bell
   2400 standard) should establish an error-free connection.  Error-
   free connections are usually indicated by the modem's verbal or
   numeric return code upon connect.

   A Multitech MNP-equipped modem may, for example, return a CONNECT
   2400/RELIABLE message, while a USRobotics HST modem would return a
   CONNECT 2400/ARQ message upon connect. Although many high-speed
   modems (ie, 9600bps and above) from different manufacturers may
   support the same level of MNP, they may use radically different
   encodingor modulation schemes to yield high data transfer rates,
   which makes them incompatible at high speeds.

   For example, the Hayes, Microcom, and USR 9600 modems all support
   MNP level 3, but are unable to communicate with each other at
   speeds higher than 2400 due to the incompatibility of their
   proprietary modulation techniques.  Most of these modems will
   automatically "fall back" to the lower speed (ie, 2400) where a
   reliable error-correcting connection can be made.