V.FC

communications, protocol 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.