First call: FreeSWITCH 192.168.10.70 send invite to 140112971507247227@85.15.0.154 offers: m=audio 26616 RTP/AVP 9 0 8 18 3 101 13 Cisco 85.15.0.154 replies with 18/SDP: m=audio 18218 RTP/AVP 0 13 101 Cisco 85.15.0.154 replies with 500 Internal Server Error Second call: FreeSWITCH 192.168.10.70 send invite to 140112971507247227@85.15.0.154 offers: m=audio 25814 RTP/AVP 18 101 13 Cisco 85.15.0.154 replied with 488 Not Acceptable Media Your Cisco is either misconfigured or is rejecting the INVITE/SDP from FreeSWITCH - you'll need to check the logs on the Cisco to see why. You should try Stevens suggestion of verbose_sdp=true and do the same two tests, but it looks like your Cisco should be happy to set the call up as G711 (PCMU) or G729 if you can get it to accept the INVITE/SDP. Regards,