Hi,

thanks for the link but I was unable to find information on how to configure my installation of FreeSwitch 1.6 to make things work.

I think I need to explain a little bit more on what I am planning to do:
FreeSwitch will be used as a SBC to the carrier. It's firewall is limited to the carriers network on the first interface.
The second interface is a local subnet where an Asterisk 13 server (PBX) is located, connecting the phones and ATAs (last with T.38 support).
For asterisk it is only necessary so set (FAXOPT(gateway)=yes) to have it detect CNG on audio and query both legs for T.38 (or receive a request in advance).
It then decides if it goes to passthru mode or transcode.

As far as I understand the FreeSwitch docs, there are these options (located in dialplan default before bridge):
<action application="set" data="fax_enable_t38=true"/> <!-- Enable t.38 for this call -->
<action application="set" data="fax_enable_t38_request=true"/> <!-- Enable t38_gateway to send a t.38 reinvite when a fax tone is detected. If using t38_gateway peer then you need to export this variable instead of set -->
<action application="set" data="execute_on_answer=t38_gateway self"/> <!--Execute t38_gateway on answer. self or peer. self: send a reinvite back to the a-leg. peer reinvite forward to the b-leg -->

<action application="export" data="fax_enable_t38=true"/> <!-- Required as of v1.6 -->
<action application="export" data="t38_passthru=true"/>

What I would like to accomplish is getting as much as T.38 I can get. The ATA should always be able to negotiate T.38 with Asterisk (which seems to work atm), FreeSwitch should then negotiate T.38 if Asterisk or the carrier asks for it (no CNG detection).
I am not sure if I can just enable t38_gateway and passthru, this case is not listed on confluence or the old wiki. Even if I do, it does not work.

FreeSwitch might need to transcode T.38 to audio for our backup carrier who does not support T.38.

Kind regards,
Kevin

2017-12-02 9:20 GMT+01:00 Raúl Alexis Betancor Santana <rbetancor@gmail.com>:
Some carriers gateways doesn't like a T.38 invite on advance, usually the order that gives better results for faxing are first invite on PCMU/PCMA (or any other supported codec) and then re-invite to T.38.

Take a look at how gonicus gofaxip do-it (https://github.com/gonicus/gofaxip)

On Fri, Dec 1, 2017 at 10:21 PM, Kevin Olbrich <ko@sv01.de> wrote:
Hi!

Our carrier supports T.38 for outgoing faxes. I am trying to send faxes like this:

originate {origination_caller_id_name='kevin',origination_caller_id_number='+49123456789',ignore_early_media=true,absolute_codec_string='PCMA,PCMU',fax_use_ecm=true,fax_enable_t38=true,fax_enable_t38_request=true}sofia/gateway/carrier_1/+4912121212 &txfax(/opt/faxout.tif)


Log:

668fd128-f2f5-4af5-9536-6780762c2efa 2017-12-01 21:38:57.513164 [DEBUG] sofia_glue.c:1295 sofia/external/+4912121212 sending invite version: 1.6.19 -36-7a77e0b 64bit
668fd128-f2f5-4af5-9536-6780762c2efa Local SDP:
668fd128-f2f5-4af5-9536-6780762c2efa v=0
668fd128-f2f5-4af5-9536-6780762c2efa o=FreeSWITCH 1512130268 1512130270 IN IP4 123.123.123.123
668fd128-f2f5-4af5-9536-6780762c2efa s=FreeSWITCH
668fd128-f2f5-4af5-9536-6780762c2efa c=IN IP4 123.123.123.123
668fd128-f2f5-4af5-9536-6780762c2efa t=0 0
668fd128-f2f5-4af5-9536-6780762c2efa m=image 30466 udptl t38
668fd128-f2f5-4af5-9536-6780762c2efa a=T38FaxVersion:0
668fd128-f2f5-4af5-9536-6780762c2efa a=T38MaxBitRate:14400
668fd128-f2f5-4af5-9536-6780762c2efa a=T38FaxFillBitRemoval
668fd128-f2f5-4af5-9536-6780762c2efa a=T38FaxRateManagement:transferredTCF
668fd128-f2f5-4af5-9536-6780762c2efa a=T38FaxMaxBuffer:2000
668fd128-f2f5-4af5-9536-6780762c2efa a=T38FaxMaxDatagram:400
668fd128-f2f5-4af5-9536-6780762c2efa a=T38FaxUdpEC:t38UDPRedundancy
668fd128-f2f5-4af5-9536-6780762c2efa
668fd128-f2f5-4af5-9536-6780762c2efa 2017-12-01 21:38:57.533158 [DEBUG] sofia.c:7084 Channel sofia/external/+4912121212 entering state [calling][0]
668fd128-f2f5-4af5-9536-6780762c2efa 2017-12-01 21:38:57.673120 [DEBUG] sofia.c:6294 sofia/external/+4912121212 T38 invite failed
668fd128-f2f5-4af5-9536-6780762c2efa 2017-12-01 21:38:57.673120 [DEBUG] sofia.c:7077 Channel sofia/external/+4912121212 skipping state [ready][488]


Carrier confirmed that T.38 is possible... What could be the cause for this? How can I enforce T.38 instead of falling back to g711a (hangup on failed invite)?

Thanks.

Kind regards,
Kevin

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