Re: [hylafax-users] Fax Extension Numbers

["Jay R. Ashworth" <jra@baylink.com>]

On Thu, Feb 15, 2001 at 12:48:12PM -0500, Joe Phillips wrote:
> On Thu, Feb 15, 2001 at 11:47:12AM -0500, Jay R. Ashworth wrote:
> > Can any of the protocol gurus comment on how much slack there is
> > between 'faxgetty answers phone' and '[something] gives up because it
> > hasn't heard a carrier from the other end yet'?
> 
> I think this is normally a pretty long time (30s maybe?)  I'm far from
> a protocol expert but a few years back I did work on NT fax software.

Ok, that's certainly long enough.

> > You know, come to think of it, the *real* problem is going to be
> > getting the receiving modem *not* to hear CNG tone, and automagically
> > *answer* the incoming call before listening for the DTMF tones, this
> > might require originally answering with ATO so that the tones could be
> > interpreted, and then re-answering with ATA... and I don't know that
> > you can do that without ATHing in the middle... which may drop calls on
> > some lines or modems.
> 
> The thing is, I think this works (in the PBX case) like so:
> - user calls fax number
> - PBX decides to route to fax modem port
> - PBX rings fax modem port
> - fax modem answers
> - PBX sends DTMFs for extension (pause?)
> - PBX opens line between caller and fax modem
> - normal fax transmission ensues
> 
> I don't think the receiver hears the CNG until *after* the
> extension DTMFs have been sent.

I've modified 'machine' to 'modem' for clarity in that paragraph.

> Thinking it through, I'd expect that the sender doesn't
> even know the call was answered until after the DTMFs were 
> sent.

See, this is the thing: if you were using a PBX, it would be
translating *incoming* DID info into DTMF, and handing it to the port
the modem was on.  If you didn't have a PBX, it would be the *user's
DTMF* that came through.  If you had a PBX, you wouldn't have to depend
on the remote sending tones at all; they'd *dial a different number*
and the PBX would translate.  But in either case, those tones have to
be sent the modem *after it goes off hook*, but *before it generates
answer tone*.  I don't know if you can do that.

> I had done some research on this a couple years back but the
> client ran out of funding before I got to implement anything
> like this.
> 
> In the non-PBX case I'd bet the user would call and send the
> DTMFs manually and hit their fax machine 'SEND' button to
> start the transmission.

Yeah, likely.  The question: what's their prompt?

> Unfortunately, I no longer have access to a PBX to test this
> so this is just a guess.

This assumes that a PBX could send DID related digits to a *station*
anyway, something I'm not at all sanguine about.

The depth of the ugliness here, obviously, is the reason why this is
still a wishlist item.  If you can't get the modem to present the
information on or after the "RING" message, before getty answers, it's
*really* ugly.

Cheers,
-- jra
-- 
Jay R. Ashworth                                                jra@baylink.com
Member of the Technical Staff     Baylink
The Suncoast Freenet         The Things I Think
Tampa Bay, Florida        http://baylink.pitas.com             +1 727 804 5015


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