Topic: Fax & Asterisk14

[compsos]

Trying to get faxing happening via asterisk. With IAXMODEM getting

Code: [Select]

WARNING[24311]: chan_sip.c:5514 process_sdp: Unsupported SDP media type in offer: image 41118 udptl t38
WARNING[24311]: chan_sip.c:5576 process_sdp: Insufficient information in SDP (c=)...
 NOTICE[24311]: chan_sip.c:5629 process_sdp: No compatible codecs, not accepting this offer!

chan_dahdi.c:4570 dahdi_handle_event: Didn't finish Caller-ID spill.  Cancelling.


This looks like  a problem between spanDSP and T.38. Adding "fax for Asterisk" did not help. From some of the docos that I read Asterisk14 does not support T.38 but only G711.  What is the best way to go with faxing?

[gippsweb]

I normally just set iaxmodem to use slin. It always seems to work for me.
I thought it was only Asterisk 1.6 that had T38 support, although I could be wrong.

[compsos]

Hi Gippsweb

From what I found Asterisk14 users g711 and 16 T.38. This came from "Fax for Asterisk" package. Also found a T38modem which is supposed to use SIP rather than IAX protocol

From http://www.voip-info.org/wiki/view/Asterisk%20T.38

• Asterisk 1.4 supports only T.38 fax pass through; there is however a third party way using HylaFax and OPAL to send and receive fax through Asterisk 1.4. See also rejected patch 12931 that includes a T.38 gateway. Attractel offers a commercial T.38 gateway solution for Asterisk. 
• In Asterisk 1.6 also origination and termination features will be added (with gateway functionality still missing) 
• NEW: In 2009 Digium introduced the commercial "Fax for Asterisk" with T.38 support (free licence for 1 channel) 

So i s the Fax for Asterisk a way to send the fax directly via asterisk without using a pseudo software modem like IAXModem or T38modem?

As I have a choice in modems (ie) ttyS0 and IAXModem sending to the same remote Voip system that has a fax machine on the TDM card via a PSTN incoming (remote end) via my TDM -->VOIP works. But when I use the IAXMODEM it fails to negotiate a speed or a carrier.

[gippsweb]

ttyS0 is for a analog modem on serial port 0, so unless you are faxing across your analog line it won't be of any use to you..

Just having a read of that wiki page you've linked to (and your quote from it) and see that 1.4 only supports T38 pass through. Basically means you need a fax machine with T38 support plugged into your asterisk box to send through it.

When I setup iaxmodem using the wiki, it setup giving the same error you show in the OP. It was due to the iaxmodem config using the wrong codec. I changed it to slin and it's been working fine since..

[compsos]

Thanks gippsweb.

The Analogue modem is working via the TDM card and then out on the VOIP connection. We are receiving faxes on the IAXMODEM ok. The test was from my system to a PSTN line connected to a TDM card with a physical Fax machine attached. We get different messages like "unable to train" or unable to negotiate a speed and the references in the console about T.38.

Client-->Hylafax-->ttyIAX-->Asterisk-->TDM-->VOIP-->PSTN--> TDM--> Asterisk-->TDM--> Fax Machine  Fails
Client-->Hylafax-->ttyS0-->TDM-->Asterisk-->VOIP-->PSTN--> TDM--> Asterisk-->TDM--> Fax Machine  Works

If my path concept is correct then it would appear to be the way it arrives into at Asterisk my end before going out.

This is the extensions conf entries.

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type=friend
username=ext2000
secret=secret
host=dynamic
qualify=3000
context=internal
callerid="ext2000" <2000>
mailbox=2000
pickupgroup=1
callgroup=1
call-limit=99
subscribecontext=extensions
deny=0.0.0.0/0.0.0.0
permit=127.0.0.1/255.255.255.0
disallow=all
allow=slin
requirecalltoken=no

[gippsweb]

your ext.conf entry is identical to mine, so I can't see that being a problem.

I don't have a TDM card in mine atm. Haven't been able to get it to work in the new setup..

Out of curiosity try adding ulaw or alaw to the available codecs

You can also do a udptl debug to see whats happening to the UDP transport layer

and a core show codecs will give you a list of available codecs on your machine..