Re: [hylafax-users] Fax Extension Numbers

[Joe Phillips <jaiger@acm.org>]

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.
 
> 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 machine port
- PBX rings fax machine port
- fax machine answers
- PBX sends DTMFs for extension (pause?)
- PBX opens line between caller and fax machine
- normal fax transmission ensues

I don't think the receiver hears the CNG until *after* the
extension DTMFs have been sent.

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

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.

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

-joe


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