[Asterisk-Dev] Fax support?

[John Paul Morrison]

With or without reinvite? With the reininvite, I would expect it to work
because
they can renegotiate to use T.38, independently of Asterisk.  But without
reinvite,
Asterisk doesn't know how to handle the codecs and would just drop fax. 

If canreinvite=no and you run Asterisk with -v you can see how fax gets
(mis)handled. 

I'm not sure how to handle dynamically assigned codecs in Asterisk. Cisco
has some IOS options where you can tell it the payload type but this would
only 
be useful for testing. 

Codecs get checked and dropped as unsupported in:

rtp.c, ast_rtp_read() around line 487 ( "Unknown RTP codec %d received\n" )
and ast_rtp_write() (grep for "Don't know how to send format %s packets with
RTP\n").
Also ast_read() in channel.c ("Dropping incompatible voice frame on %s of
format %s since our native format has changed to %s\n",)   and see
sip_write() in chan_sip.c around line 1838.

It looks like the most important thing to change is in ast_rtp_read() to get
it
to dynamically identify the codec further down in switch(rtp->f.subclass)
and calculate
the correct number of samples.  

I haven't looked any further into the code to see what the samples should be
set to, and 
there may be a better way to do this.




> -----Original Message-----
> From: asterisk-dev-bounces at lists.digium.com 
> [mailto:asterisk-dev-bounces at lists.digium.com] On Behalf Of 
> Elman Efendiyev
> Sent: Monday, September 20, 2004 2:40 PM
> To: 'Asterisk Developers Mailing List'
> Subject: RE: [Asterisk-Dev] Fax support?
> 
> 
> Im very interested in T.38 too. I think T.38 support on ZAP 
> cannels (which as I understand not to easy to implement) 
> isn't first thing asterisk needs but ability to pass T.38 
> trouth asterisk will be VERY useful. BTW, did anybody 
> succesfully used T.38 with SIP REINVITE in asterisk?
> 
> --
> Sincerely,
> Elman Efendiyev
> elman at earlinvest.com 
> 
> -----Original Message-----
> From: asterisk-dev-bounces at lists.digium.com
> [mailto:asterisk-dev-bounces at lists.digium.com] On Behalf Of 
> Andreas Sikkema
> Sent: Tuesday, September 21, 2004 12:29 AM
> To: Asterisk Developers Mailing List
> Subject: RE: Re[2]: [Asterisk-Dev] Fax support?
> 
> 
> On Mon, 2004-09-20 at 23:05, John Paul Morrison wrote:
> > On a related note, has anyone looked at passing T.38 
> through Asterisk?
> 
> > I've looked at traces between a Multitech T.38 adapter and a Cisco
> > gateway being proxied/bridged through Asterisk (I have a situation 
> > where I can't use sip reinvite).
> 
> We've seen this as well. I haven't had the time to look 
> further into this, but I'm still very interested in progress 
> in this area and willing to put some time into it.
> 
> -- 
> Andreas Sikkema <h323 at ramdyne.nl>
> 
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