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

[Brian West]

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> 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


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