[Asterisk-Users] Get faxed you faxing faxer!

[Anthony Wood]

On Tue, Aug 12, 2003 at 11:48:31AM +1000, Adam Donnison wrote:
> Fax is not as easy as it may first appear.  First of all there
> are two parts to the protocol, one of which would be relatively
> easy to accomplish if you have built your softmodem as it uses
> flow-controlled error detecting style conversations.  But this
> is just the call setup, and inter-page negotiation.  The
> actual sending of the page data uses a non-flow controlled
> protocol that uses bit stuffing to make sure the receiving fax
> receives a line of data just in time to print it.  The timings
> are _very_ tight, from memory all you need is a delay of well
> under 100ms for the remote machine to give up.  Even with
> TR29.2 modems (where the T.4 data transfer protocol timings
> are handled by the modem) you can get all sorts of problems unless
> you can make sure you keep the modem buffer full.  Doing it
> all in software means you have to manage the timings yourself.
> 
>  From my perspective, unless you are using a real-time OS, you
> may as well forget implementing T.4 as your interrupt latency
> is likely to kill you.  Either that or using a SMP machine
> so that there is always a CPU available. Either way, it is
> a big ask.

I concur.

Even hardware Class 1 faxmodems require a lot of timing dependant stuff
to happen on the server, class 2 and 2.0 can handle most of it
themselves.  My experience is with hylafax, you really want
dedicated hardware (faxcard,faxmodem class 2, or dedicated box),
to handle the fax unless you want a successful fax reception to
be the exception, rather than the rule.

Maybe if you only got faxes at night and only got asterisk calls
during the day, it would be OK, but it is amazingly annoying
that a $20 second hand 15 year old thermal fax machine
recieves every fax perfectly and hylafax still has hiccups now and then.

cheers,
Woody

> 
> Adam
> 
> Eric Wieling wrote:
> > software fax modem dsp
> > 
> > There doesn't seem to be many software fax modems out there, but I found
> > these few when doing a Google search a few months ago and bookmarked
> > them:
> > 
> > http://www.softmodem.org/
> > 
> > http://fabrice.bellard.free.fr/linmodem.html
> > 
> > http://artax.karlin.mff.cuni.cz/~pacoo0bm/archive/new_fischer/
> > 
> > http://www-users.cs.york.ac.uk/~fisher/modem/
> > 
> > I just realized that softmodem.org links to all the other URLs.
> > 
> > On Mon, 2003-08-11 at 19:23, Jamie Carl wrote:
> > 
> >>All this talk of faxing has started me thinking (this is 
> >>always a bad thing) and I've come up with a question.
> >>
> >>Now, I know Asterisk can detect and route faxes, to a 
> >>'fax' extension and all that.  But can Asterisk be used to 
> >>'receive' faxes?  
> >>
> >>I know there was some talk about this just over a year ago 
> >>and I'm wondering if anything came of it.  It would be 
> >>nice to be able to receive faxes with asterisk and then 
> >>have them filer through and AGI script and emailed or 
> >>dumped in a directory/database/whatever.
> >>
> >>I mean for me, currently, I have a fax/modem hooked up to 
> >>the same machine asterisk is on, and it get's sent faxes 
> >>via my FXS port.  It would be nice to be able to pull off 
> >>the modem and throw it away. (or auction it on ebay)
> >>
> >>
> >> --
> >>BTEL Consulting
> >>850-484-4535 x2111 (Office)
> >>504-595-3916 x2111 (Experimental)
> >>877-552-0838 (Backup Phone)
> > 
> > 
> > _______________________________________________
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> > Asterisk-Users at lists.digium.com
> > http://lists.digium.com/mailman/listinfo/asterisk-users
> 
> 
> -- 
> Adam Donnison                                  email: adam at saki.com.au
> Saki Computer Services Pty. Ltd.
> 93 Kallista-Emerald Road                        phone: +61 3 9752 1512
> THE PATCH  VIC 3792    AUSTRALIA                fax:   +61 3 9752 1098
> 
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-- 
Woody