Hi all, i'm using FS in the middle of a fax call in Default media mode without loading mod_spandsp.so `t38-passthru` profile param is enabled, and `fax_enable_t38` channel variables are exported. `Asterisk SendFax() -> FreeSWITCH -> Asterisk ReceiveFax()` call flow applied, the codec ulaw was used in all cases All Faxes are succeeded if T.38 involved but when either party is configured intentionally NOT to support T.38, g711 fax was used as expected but nearly all faxes failed (a very few fax calls success in audio mode). I tried removing FS out of the path and the g711 faxes was working fine directly. I'm not sure why so i tweaked some rtp options in FS without knowing very well what they do <param name="auto-rtp-bugs" value="clear"/> <param name="rtp-autofix-timing" value="false"/> <param name="rtp-rewrite-timestamps" value="false"/> when i tried `<param name="rtp-notimer-during-bridge" value="true"/>`, the audio faxes has higher rate of success, but the T.38 failed completely. My version is 1.6.17, tried 1.8.6 without any luck any idea or experience for making g711 fax work with FS in my case? thanks thanks Also tried Proxy media mode to let FS stayed in the path but do not touch the stream,, g711 faxes was working properly, so i guess there was some tweaks by FS default media mode into the rtp stream causing the g711 fax failure rgds, Loi Dang