Re: Using Asterisk 10.6 as a T38 Fax gateway

[Steve Underwood <steveu@xxxxxxxxxxx>]

On 07/18/2012 09:43 PM, Matthew Jordan wrote:
> ----- Original Message -----
> > From: "Alejandro Recarey" <alex@xxxxxxxxxxx>
> > To: "Asterisk Users Mailing List" <asterisk-users@xxxxxxxxxxxxxxxx>
> > Sent: Wednesday, July 18, 2012 6:30:26 AM
> > Subject:  Using Asterisk 10.6 as a T38 Fax gateway
> >
> > Hi all, and thanks for taking the time to read this.
> >
> > I am trying to configure Asterisk 10.6 as a T38 Fax gateway. I am
> > receiving calls through the PSTN and want to send them to my VoIP
> > carriers as T38. This is my dialplan:
> >
> > [fax]
> > exten => _X.,1,Set(FAXOPT(t38gateway)=yes,20)
> > exten => _X.,n,Dial(SIP/${EXTEN}@x.x.x.x)
> The correct setting is not FAXOPT(t38gateway) - that is not a valid parameter
> to pass to the FAXOPT function.  As you mention below, the correct setting
> is Set(FAXOPT(gateway)=yes).  The optional timeout is fine.
>
> https://wiki.asterisk.org/wiki/display/AST/Asterisk+10+Function_FAXOPT
>
> > I have tried with both FAXOPT(t38gateway) and FAXOPT(gateway). I have
> > also tried setting t38pt_udptl = yes,redundancy in sip.conf. None of
> > these things work. When we send a fax:
> >
> > 1. Asterisk does NOT send a REINVITE with the t38 offered. Reading
> > the
> > documentation, it should detect the fax tone with the audiohook and
> > then send a REINVITE with t38 capability.
> Have you confirmed that Asterisk does not send the re-INVITE using either
> a packet sniffer or by monitoring the log with 'sip set debug on'?  Without
> seeing the SIP message traffic and a DEBUG log, its hard to say what
> might be the cause of your issues.
>
> Typically, I would expect to see something like the following in a DEBUG log:
>
> [Jul 18 08:29:18] DEBUG[20234] res_fax.c: detected v21 preamble from SIP/ast1-g711-00000001
> [Jul 18 08:29:18] DEBUG[20234] res_fax.c: requesting T.38 for gateway session for SIP/ast1-t38-00000000
>   
> Note that this also answers your question in a subsequent e-mail: you
> should be using res_fax, with either res_fax_spandsp or Fax for Asterisk.
>
> > 2. Asterisk does not offer t38 in the SDP of the initial INVITE. This
> > is not a problem if it correctly detects and REINVITES for faxes, but
> > our destination carriers tell us that they cannot do the REINVITE
> > themselves because we do not offer t38 in our SDP, so they believe we
> > do not have that capability.
> >
> > Obviously I would prefer to just detect the fax myself and have
> > asterisk do the REINVITE.
> >
> > I have read all of the documentation on the asterisk wiki (which is
> > rather short) and anything else I could find online. Unfortunately
> > most of it is out of date and refers to asterisk versions 1.4 to 1.8,
> > which do not have T38 Gateway capability.
> There typically isn't a lot of configuration that is needed for T.38
> gateway support.  The necessary dialplan configuration is documented
> here:
>
> https://wiki.asterisk.org/wiki/display/AST/T.38+Fax+Gateway
One thing that page doesn't mention is only spandsp supports T.38 
gateway right now. The Digium FAX module does not.

Regards,
Steve


--
_____________________________________________________________________
-- Bandwidth and Colocation Provided by http://www.api-digital.com --
New to Asterisk? Join us for a live introductory webinar every Thurs:
              http://www.asterisk.org/hello

asterisk-users mailing list
To UNSUBSCRIBE or update options visit:
  http://lists.digium.com/mailman/listinfo/asterisk-users