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