I pulled the latest freeswitch from git this morning, and am still having issues using inherit_codec=true. It seems the only way I can get it to defer to the choice of the b-leg call is to remove the ringback, and thus the need for early media. My setup has 2 phones with the following codecs configured: phone1000: g722, ulaw phone1001: ulaw My goal is to have a call initiated by phone1000 (a-leg) to defer the codec choice until phone1001 (b-leg) chooses one. This would allow them to talk with no transcoding required by freeswitch. With the following dial plan, this fails to work. <extension name="Local_Extension"> <condition field="destination_number" expression="^(10[01][0-9])$"> <action application="export" data="dialed_extension=$1"/> <action application="set" data="ringback=${us-ring}"/> <action application="set" data="transfer_ringback=$${hold_music}"/> <action application="set" data="call_timeout=30"/> <action application="set" data="hangup_after_bridge=true"/> <action application="set" data="inherit_codec=true" /> <action application="bridge" data="user/${dialed_extension}@${domain_name}"/> </condition> </extension> It does log that it is going to defer: 2013-09-17 13:15:10.956535 [DEBUG] mod_sofia.c:4542 [zrtp_passthru] Setting a-leg inherit_codec=true 2013-09-17 13:15:10.956535 [DEBUG] mod_sofia.c:4545 [zrtp_passthru] Setting b-leg absolute_codec_string='G722@8000h@20i@64000b,PCMU@8000h@20i@64000b' then it tries to provide the ringback for the a-leg, and it negotiates to g722 since freeswitch supports that and it is the first match. Later when the b-leg is answered, it also negotiates, this time to ulaw as that is all b supports. My call completes, but freeswitch has to transcode between the two. In an attempt to see inherit_codec work, I then commented out the ringback line from the above dialplan. With only this one change, freeswitch now waits until the b-leg negotiation, and passes that back to the a-leg. The call completes and both handsets are using ulaw and no transcoding is required. The problem being that the calling party never gets a ring while waiting. I can't imagine that the only way to use inherit_codec=true is with all ringing turned off. Can someone tell me if there is an additional option I am missing? All documentation I read seems to indicate that just adding "inherit_codec=true" will fix things, but even the default.xml provided as an example uses ringback and therefore fails.