[Asterisk-Users] Asterisk and T38 Fax

[Andy Kuo]

Hi,

I tried to connect two T.38 capable SIP ATA's through Asterisk.
I had canreinvite=yes and the 2 ATA's did talk directly to each other,
but fax still failed.

>From Ethereal captures, I think the problem was when the originating
ATA is ready to set up a T.38 session, it sends a message to the
destination ATA to get ready for receiving T.38 packets. 
Unfortunately, Asterisk did not pass that message to the destination,
so even though the actual T.38 packets did go directly to the
destination, the destination ATA doesn't know it needs to switch to
T.38 mode.

What I am wondering is, if I can somehow configure the ATA's to be
locked to T.38 only, no voice calls allowed, will it work? (since it
is ONLY for receiving T.38 packets, we don't care if Asterisk pass on
the message to the destination to switch to T.38)

Any thoughts on whether this will work or this is just a crazy idea?

Thanks.
Andy




On 2/21/06, Lee Howard <faxguy at howardsilvan.com> wrote:
> Carey Mould wrote:
>
> > How can I get asterisk to work with faxes in my configuration? I have
> > a WAN with Asterisk at the centre and Mediatrix 1104 gateways at the
> > end nodes providing tone to legacy PBX's and fax machines. The
> > Asterisk is connected to the PSTN via a Digium single port t1.
> >
> > The end nodes are connected via frame-relay 128kbps links. I want to
> > use g.729 between the end nodes and the Asterisk box at the centre.
> > TheMediatrix box supports T38.  In my reading I am not seeing where
> > asterisk supports T38.
>
>
> I believe that currently Asterisk SVN supports T.38 pass-through to some
> extent.  Others here would be able to comment on that more fully.
> However, what you're seeking is T.38 gateway support, and Asterisk does
> not support that at the present.  I know that there is some intention
> with spandsp to get T.38 gateway support there (so Asterisk would
> eventually support T.38 gateway via Unicall), but I suspect that's a
> long way off for your present needs.  Again, I'm not really the one to
> be able to comment on this in detail.
>
> I'm not sure if the OpenH323 project (which I know supports at least
> T.38 pass-through) supports T.38 gateway, but even if it did, getting
> OpenH323 and Asterisk to work together may be difficult at best.  I'm
> not really the one to be able to comment on that in detail, either.
>
> So for the time being I would consider that Asterisk does not support
> the T.38 features that you need to make this work and that you look at a
> different approach to getting your faxing working.
>
> > 1) If a fax machine connected to the Meditrix box sends a fax to a
> > location on the PSTN (legacy fax machine) where is the T38 converted
> > back?
>
>
> That's what a T.38 gateway does.  Asterisk doesn't do it.
>
> > 2)Does Asterisk handle this?
>
>
> No.  Not yet anyway.
>
> > 3) How do I configure Asterisk to do this
>
>
> You can't presently.
>
> > 4) What is the significance on the Digium web site where they have a
> > CYA on the T1 board not  supporting faxes ?
>
>
> You probably are referring to these support statements on virtually all
> of their products: "The current state of faxing is incomplete and will
> not be supported."
>
> Well, it pretty much means what it says.  I don't think you'll get any
> significant degree of support from Digium if you run into trouble with
> faxing using their hardware.
>
> All of that said, can you push a fax call through an Asterisk PBX?
> Yes.  Search the archives and you'll see it can be done.
>
> Lee.
>
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