[Asterisk-Dev] FAX Subsystem discussion.

[John Harragin]

A couple more thoughts I wanted to mention. It is likely that an existing
fax server would regard it's self as a real-time application. It is possible
that operating this program and asterisk at the same time could lead to
compromised operation of one or both.

Another thing was that I was basing my position on an assumption that fax
protocol handshaking has stringent timing requirements. It is possible that
this is not the case and replys might just be waited for. If so, reliable
fax transmission streams might be accomplished with a special echocan that
takes advantage of the one-sided-ness of a fax transmission. Mark's
daggressive_suppresion might be tweeked for this without too much change.
I'll see what i can find out...

John

> > What I am most interested in is a way to attach a fax to an Asterisk FXS
> > port and then connect through IAX (prefered) to another asterisk system
> > to connect to a T1 card for transmission to the PSTN.
> >
> > Fax - FXS - * - WAN - * T1 - PSTN.
> >
> > While direct conversion of the channel to a bitstream over IAX would be
> nice,
>
> > ...a store and forward would do in most cases.
>
> This is what I am proposing. I think it would be easier and much more
solid
> than attempting to send the fax stream over IP (In your case, it would be
> very simple to apply compression to the intermediate file prior to
> transmission). If we persued the other route of streaming the fax data
> live,there would be issues with handshaking through transmission delay,
echo
> problems, some fax machines would be more stringent regarding handshake
> timings, we would need special echocans, the transmission rate would be
> low - in fact this would probably lead to overall slower faxing, higher
> telco minutes, the list would go on and on. Because of this, building a
> virtual device driver for hylafax would ultimately be a waste of time.
> However, utilizing its functional blocks might be great, as it already
does
> almost all of the things we need...
>
> Additionally, it might be done in a new cvs agtools (asterisk gpled tools)
> we could use big parts of a gpled fax program (providing a suitable one
> exists) - since it would be a separate app wouldn't this approach not
> interfere with the Asterisk licence? Or, if hylafax source lends itself to
> queue then transmit - there would be no problem (see below). We also might
> talk to the hylafax developers - as they might be interested in
maintaining
> asterisk call functionality in their source - * would give them a lot
too...
>
> John