V.E.R.A. -- Virtual Entity of Relevant Acronyms (February 2016):

VFC
       V. Fast Class (MODEM), "V.FC"


The Free On-line Dictionary of Computing (30 December 2018):

V.FC

    A serial line protocol supported
   by some modems.  Uses symbol rates of 2400, 2800, 3000,
   >3200 and 3429 and up to 28800 baud.

   V.34 modems will also support V.FC if the manufacturer
   currently supports V.FC.

   The first V.FC modems were shipped in November 1993 and there
   have been many thousands sold.  There will probably be in
   excess of a million V.FC modems installed by the end of 1994.

   V.FC was intended to take some of the techniques being
   proposed for V.34 and put them into a real modem that people
   could use.  This also gave a lot of people the opportunity to
   try out 28.8 kilobit per second operation for the first time.
   There was never any intention from Hayes or Rockwell (who
   worked together for two years on V.FC) that V.FC would be
   compatible with V.34 - even if they had wanted it, others
   would have made sure it didn't happen!  In fact, they made the
   start-up deliberately different from V.34 so that it would be
   easy to distinguish between the two and easier to make
   dual-mode V.FC/V.34 modems.

   V.FC is quite different from V.34.  Most of the
   signal-processing algorithms, whilst based on the same
   theory, are implemented in different ways.  V.34 has some
   extra things like a secondary channel and a special mode for
   28.8 kilobit per second fax.

   The Rockwell V.FC implementation uses a single-chip
   mask-programmed DSP for all the signal processing functions.
   You can also buy a modem controller chip from Rockwell to go
   with it which implements AT commands, error-control and
   compression.  Hayes made their own controller using the
   Motorola 68302 processor.  When it comes to an upgrade
   from V.FC to V.34 you have to have a new, masked DSP chip and
   new controller firmware to implement all the V.34-specific
   features.  This means that Rockwell-DSP based modems must be
   returned to the manufacturer for upgrade.  Upgraded modems
   will talk to either V.FC or V.34 modems.