[asterisk-users] My Asterisk can not send fax via T.38

[Weiqi]

Hello,

I am a newer on asterisk. when I tried to send fax, I can not get success.
After doing a lot of reseach, I decide to ask my question at here.

Instead of using old fax machine, I want my system can send fax via t.38.
Could anyone  give me some idea to correct my configuration?

Thanks a lot!
Here is the detail:

my system: *ubuntu 14.04 + asterisk 11.7*

I use apt-get to install the ubuntu default version of asterisk 11.7. for
easy debug, I just change a few param value with the default version
sip.conf

t38pt_udptl = yes,redundancy,maxdatagram=400
faxdetect = yes

extension.conf

[sendFAX]
exten => s,1,VERBOSE(sending fax...)
exten => s,n,Set(FAXOPT(headerinfo)=Fax from a Demo test)
exten => s,n,SendFAX(/tmp/demo.tiff,f)
;I get demo.tiff file from "$ gs -q -dNOPAUSE -dBATCH -sDEVICE=tiffg4
-sPAPERSIZE=letter -sOutputFile=<dest> <src>"
exten => s,n,VERBOSE(ok!)
exten => s,n,Hangup

I use AMI to originate a fax call. In the CLI, everything looks well. I
didn't get any error message. When I use wireshark to check the detail of
this comunication, I found Asterisk used G711 instead of using T.38 which
is expected.

however, at the receiver end, I didn't receive the fax, and I just got a
error "Dcn No Dis"
After a research, I got this:

T.30 Fax Signaling Messages In a Voip fax call, T.38 packets are preceded
and succeeded by T.30 fax signaling messages. These messages include:


   1. DIS: Digital Identification Signal indicating terminating fax
   capabilities (for example, data rate)
   2. DCS: Digital Command Signal indicating transmission mode that will be
   used by originating fax (for example, transfer rate)
   3. TCF: Training Check Sequences (sent for 1.5 seconds)
   4. CFR: Confirmation To Receive indicating the receiving fax is ready to
   receive the document
   5. MPS: MultiPage Signal (sent after each page if more than one page is
   sent)
   6. MCF: Message Confirmation indicating the page was received
   7. EOP: End Of Procedure message indicating there are no more pages to
   be sent
   8. DCN: Disconnect message

 Additional optional messages:

1.CSI: Called Subscriber Identification

2.TSI: Transmitting Subscriber Identification

But I am still confused with what "Dcn No Dis" means what's wrong with my
asterisk system.

I am sure of these:

   1. the receiver is working well.
   2. My ISP provider is fully support fax termination both in g711 and t.38
   3. My testing server is not behind any firewall.

The demo.jpg <http://goo.gl/ix8JzY> is my wireshark's screenshot. form 19
to 1841, all traffic are RTP package.

The t.38 png <http://goo.gl/lpD7Z5> diagram illustrates is a typical fax
call.
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