Hi, Seems to me that I'm not configuring something correctly or hitting some bug. Reading https://wiki.freeswitch.org/wiki/Mod_spandsp#t38_gateway I have a T.38 incapable provider that will respond with SIP 488 back. If I leave T.38-passtrough and get 488 back, RTP stops and call is dropped. So I was trying to set up correct transcoding. This is the scenario, with 3 identical FS: 1 - T.38 incapable server - PROVIDER 2 - T.38 capable - PROXY 3 - T.38 capable - PBX PBX sends txfax (file.tiff) to PROXY which forwards call to PROVIDER (g.711). PBX sends T.38 re-Invite, PROXY responds with 200 OK but then I have 2 scenarios: either passtrough T.38 which will invoke 488 and dropped call or I tried sip_execute_on_image=t38_gateway peer nocng" but this doesn't send anything to PROVIDER but also call is dropped after BYE and 486 message. Case that I'm hitting is similar to this: "If you want to transcode t.38 on leg a to audio on leg B when leg a invites t.38, but refuse all t.38 offers from leg b " but to refuse t.38 invites from lag a. The other way around, call from PROVIDER to PBX over PROXY is easely transcoded with sip_execute_on_image=t38_gateway self nocng" on the PROXY side. Is it normal behaviour that After failed t.38 negotiation or 488 message, fax call doesn't fall back to previous codec or t.30? -- Regards, Mirko