vfc
     v. fast class modem, "v.fc"
     
     

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.
     
     
see also:
protocol modems symbol rates baud v.34 hayes 
rockwell algorithm secondary channel dsp compression 
motorola 68302 firmware