Re: flexfax: modem 1000$ question

["Larry Lipstone" <lrl@stoneware.com>]

Jay R. Ashworth wrote...
> 
> On Mon, Sep 13, 1999 at 04:41:03PM -0700, Larry Lipstone wrote:
> > Jay R. Ashworth wrote...
> > > Apparently some modems can listen for CNG on the line before answering,
> > > to allow them to distinguish incoming fax calls, which they should
> > > answer, from incoming voice calls, which they shouldn't.
> > > 
> > > Inasmuch as most CO switches no longer send transmit audio until the
> > > call is answered, I don't see why this might be useful, but what they
> > > hey...
> > 
> > Probably to share the line with an answering machine (or maybe even a
> > human?), so that it will pick up the line only for a fax call, taking
> > the call away from the machine or other being.
> 
> Yes, Larry, but you missed the thrust of my comment: in most cases, if
> the call coming in is not local, and even sometimes if it is, the CNG
> tones will not be passed to the called line by the switch, so they will
> not be there for the modem to hear, until it goes off hook.

I really thought twice about extending this thread, but what the heck!

While what you say is quite true -- that there is often no forward voice
path from the caller to the called line until the called line answers --
the cases where I have seen this feature used are where the answering
machine and fax device are connected in parallel, and the answering
machine answers the call immediately while the fax device passively
listens.  Since the machine has answered, there is a voice path, and the
fax device will hear the CNG tone if it's being sent.

If it does hear it, generally while the answering machine's greeting is
being played, it answers the call also.  Hopefully you've got the
kind of answering machine that detects that event and releases the call
itself, so the call is effectively switched to the fax box.

OK, that was my 2c.  Now back to real work...

Larry