Hi; I am attempting to get T38 Fax working between two FS/FusionPBX installations using mod_spandsp. I am unable to get into T.38 mode, T.30 used, successful fax. Note that zrtp is disabled for fax calls, due to T38 udpl (not rtp media) incompatibility Thanks Brian West!: "T.38 Fax takes place over UDPTL, There for it can NOT be encrypted as there was never really a standard for doing so." Details (both FS's): SIP Provider: freephoneline.ca (claims T38 capable) freeswitch - 1.4.18 x86_64 Topology: FS#1: rossco.org, using FusionPBX web GUI to send fax FS#2:rossco.duckdns.org, using spandsp extension to receive fax (spandsp txfax, x1020)FS#1 -> cloud -> FS#2(spandsp rxfax, x9000) Key variables for fax sender (FS#1), during call: $domain= rossco.org Spandsp Fax extension: 1020 t38_passthru = false zrtp_secure_media = false fax_enable_t38 = true fax_enable_t38_request = true fax_use_ecm = off inbound-late-negotiation = true ignore_early_media = false Key variables for fax receiver (FS#2), during call: $domain= rossco.duckdns.org Spandsp Fax extension: 9000 t38_passthru = false zrtp_secure_media = false fax_enable_t38 = true fax_enable_t38_request = true fax_use_ecm = off inbound-late-negotiation = true ignore_early_media = false Full Logs w/siptrace: Sender(rossco.org): https://pastebin.freeswitch.org/24115 Receiver(rossco.duckdns.org): https://pastebin.freeswitch.org/24116 Note that the SDP's are correct for T38: 590fc4c4-3035-438e-a4c7-4a9d8e51ee42 v=0 590fc4c4-3035-438e-a4c7-4a9d8e51ee42 o=FreeSWITCH 1428750600 1428750602 IN IP4 198.48.238.130 590fc4c4-3035-438e-a4c7-4a9d8e51ee42 s=FreeSWITCH 590fc4c4-3035-438e-a4c7-4a9d8e51ee42 c=IN IP4 198.48.238.130 590fc4c4-3035-438e-a4c7-4a9d8e51ee42 t=0 0 590fc4c4-3035-438e-a4c7-4a9d8e51ee42 m=image 16448 udptl t38 590fc4c4-3035-438e-a4c7-4a9d8e51ee42 a=T38FaxVersion:0 590fc4c4-3035-438e-a4c7-4a9d8e51ee42 a=T38MaxBitRate:14400 590fc4c4-3035-438e-a4c7-4a9d8e51ee42 a=T38FaxFillBitRemoval 590fc4c4-3035-438e-a4c7-4a9d8e51ee42 a=T38FaxRateManagement:transferredTCF 590fc4c4-3035-438e-a4c7-4a9d8e51ee42 a=T38FaxMaxBuffer:2000 590fc4c4-3035-438e-a4c7-4a9d8e51ee42 a=T38FaxMaxDatagram:400 590fc4c4-3035-438e-a4c7-4a9d8e51ee42 a=T38FaxUdpEC:t38UDPRedundancy Questions: 1 - According to my interpretation of logs, T38 is not negotiated, despite T38 SDP's 2 - What am I missing? Thanks; Bill Ross