Vendor-specific Notes
                                       
   Exar seems to be similar to ZyXEL in that they implement only a
   portion of the de facto Class 2 specification. Exar implements Class1
   in it's newer firmware.
   
   Rockwell has adopted the Hayes ATI4 extensions documented in the Hayes
   Technical Reference for listing product features and supported speeds
   Rockwell seems to be implementing Class1 in all of it's firmware for
   more recent firmware. Rockwell is not implementing as much of the de
   facto Class 2 specification in the newer firmware for 144DP and 2496
   models as in the older firmware for the 2496 models
   
   Sierra has a strange error reporting technique for commands like
   AT+FJUNK since what they return is '000\r\nOK' which doesn't really
   make much sense but seems to be consitant in any Sierra based
   products.
   
   ZyXEL has a problem with returning OK for commands which they don't
   implement. This makes it hard to determine if a command works or not.
   ZyXEL implements the following commands only: +FAA=, +FCLASS=,
   +FCLASS=?, +FCLASS?, +FCR=, +FDCC=, +FDCS:, +FDIS=, +FDR, +FDT, +FET=,
   +FLID=, +FMDL?, +FMFR?, +FREV? They had bugs with the handling of
   +FLID and the handling of "s. They also had bugs with the reporting of
   the +FCSI: string in that it was truncated to 19 characters. These
   have all been fixed in later ROM releases.
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    Sam Leffler. Last updated $Date: 1994/10/19
    23:53:53 $.