asterisk users - Feb 2006 - Asterisk and T38 Fax

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.

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?
2)Does Asterisk handle this?
3) How do I configure Asterisk to do this
4) What is the significance on the Digium web site where they have a CYA 
on the T1 board not  supporting faxes ?

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.