Hi all, I've been having a problem with a new provider with sending them faxes over T.38. I don't think FreeSWITCH is to blame at all, but maybe FS can fix my issue, or someone here can help me find the cause of the problem ? The call flow is as follows: CPE 1.1.1.1 | V 2.2.2.2 FreeSWITCH 3.3.3.3 | V 4.4.4.4 Provider In FreeSWITCH, I've set t38-passthru to true on the profile where the CPE INVITEs to. Further, I'm doing late negotiation (while offering the a-leg codecs to the b-leg and the other way around). RTP is flowing through FS. In short, this is happening: CPE -> FS -> Provider INVITE (with audio PCMA, PCMU codecs) Provider -> FS -> CPE 200 OK (with audio PCMA) CPE -> FS -> Provider reINVITE (with T.38 in SDP) Provider -> FS -> CPE 200 OK (with T.38 in SDP - although with different error correction, is this a problem?) Provider -> FS -> CPE reINVITE (again with T.38 in SDP) CPE -> FS -> Provider 200 OK (with T.38 in SDP) CPE -> FS -> Provider reINVITE (with T.38 in SDP) Provider -> FS -> CPE BYE (of course, or it'll loop forever) Does a setting in FreeSWITCH exist so that it can change the error correction (because both endpoints seem to want a different one ?) Could that be the cause of the problem ? Hope anyone can help. Thanks, Leon Here's the trace - I left out the tryings, acks, removed some unnecessary sip headers to make things a bit less verbose: U 2012/08/23 15:34:16.334938 3.3.3.3:5060 -> 4.4.4.4:5060 INVITE sip:+888@4.4.4.4 SIP/2.0. From: "+777" <sip:+777@provider.voip.tel>;tag=70aprjj2Z1QKK. To: <sip:+888@4.4.4.4>. Call-ID: 3bf65bb6-ed27-11e1-a810-1d8ba1d695aa. CSeq: 32528364 INVITE. Contact: <sip:gw+provider-voip-tel@3.3.3.3:5060;transport=udp;gw=provider-voip-tel>. Content-Type: application/sdp. Content-Disposition: session. Content-Length: 253. X-Designated-Service: fax/t38. . v=0. o=FreeSWITCH 1345708964 1345708965 IN IP4 3.3.3.3. s=FreeSWITCH. c=IN IP4 3.3.3.3. t=0 0. m=audio 19892 RTP/AVP 8 0 101 13. a=rtpmap:8 PCMA/8000. a=rtpmap:0 PCMU/8000. a=rtpmap:101 telephone-event/8000. a=fmtp:101 0-16. a=ptime:30. U 2012/08/23 15:34:18.192303 4.4.4.4:5060 -> 3.3.3.3:5060 SIP/2.0 180 Ringing. From: "+777" <sip:+777@provider.voip.tel>;tag=70aprjj2Z1QKK. To: <sip:+888@4.4.4.4>;tag=SDkvc5299-1.45.133.551104+1+a1b50004+4166b8ad. Call-ID: 3bf65bb6-ed27-11e1-a810-1d8ba1d695aa. CSeq: 32528364 INVITE. Server: DC-SIP/2.0. Content-Length: 0. Contact: <sip:+888@4.4.4.4:5060;transport=udp>. . U 2012/08/23 15:34:23.904745 4.4.4.4:5060 -> 3.3.3.3:5060 SIP/2.0 200 OK. From: "+777" <sip:+777@provider.voip.tel>;tag=70aprjj2Z1QKK. To: <sip:+888@4.4.4.4>;tag=SDkvc5299-1.45.133.551104+1+a1b50004+4166b8ad. Call-ID: 3bf65bb6-ed27-11e1-a810-1d8ba1d695aa. CSeq: 32528364 INVITE. Server: DC-SIP/2.0. Contact: <sip:+888@4.4.4.4:5060;transport=udp>. Content-Type: application/sdp. Content-Length: 229. . v=0. o=- 3554717663 3554717663 IN IP4 4.4.4.4. s=-. c=IN IP4 4.4.4.4. t=0 0. m=audio 22054 RTP/AVP 8 101. a=ptime:30. a=rtpmap:8 PCMA/8000. a=rtpmap:101 telephone-event/8000. a=fmtp:101 0-15. a=silenceSupp:off - - - -. U 2012/08/23 15:34:23.996849 3.3.3.3:5060 -> 4.4.4.4:5060 INVITE sip:+888@4.4.4.4:5060;transport=udp SIP/2.0. From: "+777" <sip:+777@provider.voip.tel>;tag=70aprjj2Z1QKK. To: <sip:+888@4.4.4.4>;tag=SDkvc5299-1.45.133.551104+1+a1b50004+4166b8ad. Call-ID: 3bf65bb6-ed27-11e1-a810-1d8ba1d695aa. CSeq: 32528365 INVITE. Contact: <sip:gw+provider-voip-tel@3.3.3.3:5060;transport=udp;gw=provider-voip-tel>. Content-Type: application/sdp. Content-Disposition: session. Content-Length: 339. X-Designated-Service: fax/t38. . v=0. o=FreeSWITCH 1345708964 1345708966 IN IP4 3.3.3.3. s=FreeSWITCH. c=IN IP4 3.3.3.3. t=0 0. m=image 19892 udptl t38. a=T38FaxVersion:0. a=T38MaxBitRate:14400. a=T38FaxTranscodingMMR. a=T38FaxTranscodingJBIG. a=T38FaxRateManagement:transferredTCF. a=T38FaxMaxBuffer:500. a=T38FaxMaxDatagram:512. a=T38FaxUdpEC:t38UDPFEC. U 2012/08/23 15:34:24.093598 4.4.4.4:5060 -> 3.3.3.3:5060 SIP/2.0 200 OK. From: "+777" <sip:+777@provider.voip.tel>;tag=70aprjj2Z1QKK. To: <sip:+888@4.4.4.4>;tag=SDkvc5299-1.45.133.551104+1+a1b50004+4166b8ad. Call-ID: 3bf65bb6-ed27-11e1-a810-1d8ba1d695aa. CSeq: 32528365 INVITE. Server: DC-SIP/2.0. Contact: <sip:+888@4.4.4.4:5060;transport=udp>. Content-Type: application/sdp. Content-Length: 272. . v=0. o=- 3554717663 3554717664 IN IP4 4.4.4.4. s=-. c=IN IP4 4.4.4.4. t=0 0. m=image 22054 udptl t38. a=T38FaxVersion:0. a=T38MaxBitRate:14400. a=T38FaxRateManagement:transferredTCF. a=T38FaxMaxBuffer:72. a=T38FaxMaxDatagram:316. a=T38FaxUdpEC:t38UDPRedundancy. U 2012/08/23 15:34:33.885255 4.4.4.4:5060 -> 3.3.3.3:5060 INVITE sip:gw+provider-voip-tel@3.3.3.3:5060;transport=udp;gw=provider-voip-tel SIP/2.0. Call-ID: 3bf65bb6-ed27-11e1-a810-1d8ba1d695aa. From: <sip:+888@4.4.4.4>;tag=SDkvc5299-1.45.133.551104+1+a1b50004+4166b8ad. To: "+777" <sip:+777@provider.voip.tel>;tag=70aprjj2Z1QKK. CSeq: 693734809 INVITE. Contact: <sip:+888@4.4.4.4:5060;transport=udp>. Content-Type: application/sdp. Content-Length: 272. . v=0. o=- 3554717663 3554717665 IN IP4 4.4.4.4. s=-. c=IN IP4 4.4.4.4. t=0 0. m=image 22054 udptl t38. a=T38FaxVersion:0. a=T38MaxBitRate:14400. a=T38FaxRateManagement:transferredTCF. a=T38FaxMaxBuffer:72. a=T38FaxMaxDatagram:316. a=T38FaxUdpEC:t38UDPRedundancy. U 2012/08/23 15:34:33.939092 3.3.3.3:5060 -> 4.4.4.4:5060 SIP/2.0 200 OK. From: <sip:+888@4.4.4.4>;tag=SDkvc5299-1.45.133.551104+1+a1b50004+4166b8ad. To: "+777" <sip:+777@provider.voip.tel>;tag=70aprjj2Z1QKK. Call-ID: 3bf65bb6-ed27-11e1-a810-1d8ba1d695aa. CSeq: 693734809 INVITE. Contact: <sip:gw+provider-voip-tel@3.3.3.3:5060;transport=udp;gw=provider-voip-tel>. Accept: application/sdp. Content-Type: application/sdp. Content-Disposition: session. Content-Length: 345. . v=0. o=FreeSWITCH 1345708964 1345708967 IN IP4 3.3.3.3. s=FreeSWITCH. c=IN IP4 3.3.3.3. t=0 0. m=image 19892 udptl t38. a=T38FaxVersion:0. a=T38MaxBitRate:14400. a=T38FaxTranscodingMMR. a=T38FaxTranscodingJBIG. a=T38FaxRateManagement:transferredTCF. a=T38FaxMaxBuffer:72. a=T38FaxMaxDatagram:512. a=T38FaxUdpEC:t38UDPRedundancy. U 2012/08/23 15:34:33.950201 3.3.3.3:5060 -> 4.4.4.4:5060 INVITE sip:+888@4.4.4.4:5060;transport=udp SIP/2.0. From: "+777" <sip:+777@provider.voip.tel>;tag=70aprjj2Z1QKK. To: <sip:+888@4.4.4.4>;tag=SDkvc5299-1.45.133.551104+1+a1b50004+4166b8ad. Call-ID: 3bf65bb6-ed27-11e1-a810-1d8ba1d695aa. CSeq: 32528366 INVITE. Contact: <sip:gw+provider-voip-tel@3.3.3.3:5060;transport=udp;gw=provider-voip-tel>. User-Agent: c4-provider-ims-intx. Content-Type: application/sdp. Content-Disposition: session. Content-Length: 338. X-Designated-Service: fax/t38. . v=0. o=FreeSWITCH 1345708964 1345708968 IN IP4 3.3.3.3. s=FreeSWITCH. c=IN IP4 3.3.3.3. t=0 0. m=image 19892 udptl t38. a=T38FaxVersion:0. a=T38MaxBitRate:14400. a=T38FaxTranscodingMMR. a=T38FaxTranscodingJBIG. a=T38FaxRateManagement:transferredTCF. a=T38FaxMaxBuffer:72. a=T38FaxMaxDatagram:512. a=T38FaxUdpEC:t38UDPFEC. U 2012/08/23 15:34:34.043165 4.4.4.4:5060 -> 3.3.3.3:5060 BYE sip:gw+provider-voip-tel@3.3.3.3:5060;transport=udp;gw=provider-voip-tel SIP/2.0. Call-ID: 3bf65bb6-ed27-11e1-a810-1d8ba1d695aa. From: <sip:+888@4.4.4.4>;tag=SDkvc5299-1.45.133.551104+1+a1b50004+4166b8ad. To: "+777" <sip:+777@provider.voip.tel>;tag=70aprjj2Z1QKK. CSeq: 693734810 BYE. Content-Length: 0. Reason: Q.850; cause=41;text="Temporary failure". .