[Freeswitch-users] PROTOCOL_WARNING when sending a fax via T.38

Fri Sep 18 19:06:00 MSD 2015

I was able to reproduce the problem also in our lab environment. Now I have a setup with 3 freeswitches (All have version 1.4.21):

freeswitch1 (Sangoma A200 Card) <—TDM—> freeswitch2 (Sangoma A200 Card) <- SIP/T.38 —> freeswitch3

freeswitch1 and freeswitch2 are connected via TDM with an E1 crossed cable. freeswitch3 has only a SIP profile running. From freeswitch1, I originate the fax with

fs_cli -x "originate freetdm/1/a/02211111111111 &txfax(/tmp/lenna-colour.tif)"

 then freeswitch1 sends the fax via TDM to freeswitch2.

  <extension name="fax-over-ip-test">
      <condition field="destination_number" expression="^(02211111111111)$">
        <action application="log" data="INFO Incoming TEST FAX" />
        <action application="export" data="fax_verbose=true" />
        <action application="export" data="fax_enable_t38=true" />
        <action application="export" data="fax_enable_t38_request=true" />
        <action application="export" data="execute_on_answer=t38_gateway self" />
        <action application="bridge" data="sofia/external/${destination_number}@192.168.1.151" />
        <action application="hangup" data="NORMAL_CLEARING" />
      </condition>
    </extension>

freeswitch2 then sends the fax via SIP/T.38 to freeswitch 3, where the fax is finally received:

<condition field="destination_number" expression="^(02211111111111)$">
        <action application="log" data="INFO Incoming TEST FAX" />
        <action application="answer" />
        <action application="playback" data="silence_stream://2000"/>
        <action application="set" data="fax_enable_t38_request=true"/>
        <action application="set" data="fax_enable_t38=true"/>
        <action application="rxfax" data="/tmp/FAX-${uuid}.tif"/>
        <action application="hangup"/>
      </condition>

On freeswitch2, which acts in this case as TDM->T.38 gateway, I can see the same protocol error. See the full log here: 

freeswitch2: https://pastebin.freeswitch.org/24400 <https://pastebin.freeswitch.org/24400>
freeswitch3: https://pastebin.freeswitch.org/24401 <https://pastebin.freeswitch.org/24401>

Let me know how I can analyze the problem, maybe it helps if I add more log/debug  messages to mod_spandsp and the test again? With debugging freeswitch I’m not familiar yet ...

Thanks and Regards

Markus 

> Am 18.09.2015 um 02:18 schrieb Brian West <brian at freeswitch.org <mailto:brian at freeswitch.org>>:
> 
> The write_frame failed, but without some debugging in there to see why, I could only guess at this point, I don't have the TDM setup you do to verify it.
> 
> On Thu, Sep 17 , 2015 at 5:58 PM, Markus Bönke <mbodbg at gmx.net <mailto:mbodbg at gmx.net>> wrote:
> I just upgraded to 1.4.21, but it is the same issue.
> 
>> Am 18.09.2015 um 00:08 schrieb Brian West <brian at freeswitch.org <mailto:brian at freeswitch.org>>:
>> 
>> Try on 1.4.21?  We did fix an issue in this area where the CNG packets were causing issues with t.38.
>> 
>> /b
>> 
>> On Thursday, September 17, 2015, Markus Bönke <mbodbg at gmx.net <mailto:mbodbg at gmx.net>> wrote:
>> Hello,
>> 
>> I want to send a fax between two freeswitches (1.4.20) via T.38. On the SENDER freeswitch, I have Sangoma A104 TDM card and use the following dialplan:  
>> 
>>         <action application="export" data="fax_enable_t38=true"/>
>>         <action application="export" data="fax_enable_t38_request=true"/>
>>         <action application="export" data="fax_verbose=true"/>
>>         <action application="export" data="execute_on_answer=t38_gateway self"/>
>>         <action application="bridge" data="sofia/external/${destination_number}@${destination_ip}"/>
>> 
>> On the RECEIVER freeswitch I use the this dialplan:
>> 
>>          <action application="answer" />
>>          <action application="playback" data="silence_stream://2000"/>
>>          <action application="set" data="fax_enable_t38_request=false"/>
>>          <action application="export" data="fax_enable_t38=true"/>
>>          <action application="rxfax" data="/tmp/FAX-${uuid}.tiff"/>
>> 
>> When I try to send a fax, on the RECEIVER freeswitch, I can see in the (second) INVITE the T.38 data is present: 
>> 
>> ...
>>   a=T38FaxVersion:0
>>    a=T38MaxBitRate:14400
>>    a=T38FaxFillBitRemoval
>>    a=T38FaxRateManagement:transferredTCF
>>    a=T38FaxMaxBuffer:2000
>>    a=T38FaxMaxDatagram:400
>>    a=T38FaxUdpEC:t38UDPRedundancy
>> …
>> 
>> On the SENDER side I can see that it tries to start the t38_gateway
>> 
>> …
>> 2015-09-17 23:36:51.092799 [DEBUG] mod_spandsp_fax.c:286 FLOW T.38 Rx     2: IFP 00
>> 2015-09-17 23:36:51.092799 [DEBUG] mod_spandsp_fax.c:286 FLOW T.38 Rx     2: indicator no-signal
>> 2015-09-17 23:36:51.092799 [DEBUG] mod_spandsp_fax.c:286 FLOW T.38G Changing - (0) ced -> no-signal
>> 2015-09-17 23:36:51.092799 [DEBUG] mod_spandsp_fax.c:286 FLOW T.38G Changing to no-signal
>> 2015-09-17 23:36:51.092799 [DEBUG] mod_spandsp_fax.c:286 FLOW T.38G Non-ECM mode
>> 2015-09-17 23:36:51.172799 [DEBUG] mod_spandsp_fax.c:286 FLOW T.38 Rx     3: IFP 06
>> 2015-09-17 23:36:51.172799 [DEBUG] mod_spandsp_fax.c:286 FLOW T.38 Rx     3: indicator v21-preamble
>> 2015-09-17 23:36:51.172799 [DEBUG] mod_spandsp_fax.c:286 FLOW T.38G Changing - (0) no-signal -> v21-preamble
>> 2015-09-17 23:36:51.172799 [DEBUG] mod_spandsp_fax.c:286 FLOW T.38G Changing to v21-preamble
>> 2015-09-17 23:36:51.172799 [DEBUG] mod_spandsp_fax.c:286 FLOW T.38G Non-ECM mode
>> 2015-09-17 23:36:52.072799 [DEBUG] mod_spandsp_fax.c:286 FLOW T.38G HDLC underflow at 4
>> 2015-09-17 23:36:52.172799 [DEBUG] mod_spandsp_fax.c:286 FLOW T.38 Rx     4: IFP c0 01 80 00 00 ff
>> 2015-09-17 23:36:52.172799 [DEBUG] mod_spandsp_fax.c:286 FLOW T.38 Rx     4: (0) data v21/hdlc-data + 1 byte(s)
>> …
>> 
>> But then fails with a protocol error
>> 
>> 2015-09-17 23:34:07.652799 [DEBUG] mod_spandsp_fax.c:286 FLOW T.38 Tx     1: indicator v21-preamble
>> 2015-09-17 23:34:07.652799 [ERR] mod_spandsp_fax.c:659 INVALID WRITE: 8:3
>> 2015-09-17 23:34:07.652799 [ERR] mod_spandsp_fax.c:671 TERMINATING T30 STATE
>> …
>> 2015-09-17 23:34:07.652799 [WARNING] mod_spandsp_fax.c:286 PROTOCOL_WARNING T.38 Tx packet handler failure
>> 
>> On the RECEIVER side the fax fails with „result (49) The call dropped prematurely“. Can this be because of a wrong configuration (dialplans/mod_spandsp), or is this a bug?
>> 
>> Thanks and Regards
>> 
>> Markus 
>> 
>> 
>> 
>> -- 
>> Brian West
>> brian at freeswitch.org <mailto:brian at freeswitch.org>
>> 
>> Twitter: @FreeSWITCH , @briankwest
>> http://www.freeswitchbook.com <http://www.freeswitchbook.com/>
>> http://www.freeswitchcookbook.com <http://www.freeswitchcookbook.com/>
>> Got Bugs? Report them here <https://freeswitch.org/jira>! | Reddit: /r/freeswitch <https://www.reddit.com/r/freeswitch>
>> T:+19184209001 <tel:%2B19184209001> | F:+19184209002 <tel:%2B19184209002> | M:+1918424WEST (9378)
>> iNUM:+883 5100 1420 9001 | ISN:410*543 | Skype:briankwest
>> 
>> 
>> _________________________________________________________________________
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> 
> _________________________________________________________________________
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> 
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> 
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> 
> 
> 
> -- 
> Brian West
> brian at freeswitch.org <mailto:brian at freeswitch.org>
> 
> Twitter: @FreeSWITCH , @briankwest
> http://www.freeswitchbook.com <http://www.freeswitchbook.com/>
> http://www.freeswitchcookbook.com <http://www.freeswitchcookbook.com/>
> Got Bugs? Report them here <https://freeswitch.org/jira>! | Reddit: /r/freeswitch <https://www.reddit.com/r/freeswitch>
> T:+19184209001 | F:+19184209002 | M:+1918424WEST (9378)
> iNUM:+883 5100 1420 9001 | ISN:410*543 | Skype:briankwest
> 
> _________________________________________________________________________
> Professional FreeSWITCH Consulting Services: 
> consulting at freeswitch.org <mailto:consulting at freeswitch.org>
> http://www.freeswitchsolutions.com
> 
> Official FreeSWITCH Sites
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> 
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