Hi All, I am doing the call from the A Endpoint to B Endpoint using FreeSwitch In Between When FreeSwitch Get the INVITE Request from the A Endpoint, I am using the following absolute_codec_string. absolute_codec_string = "PCMU,PCMA,G726-40,G726-32,G726-24,G726-16,G729,GSM,L16,ILBC,G723" FreeSwitch is also sending the INVITE Request to B Leg with the codecs defining in the absolute_codec_string. Which is as below. 592f8a31-4978-1233-90b2-d4ae52cde95f] send 1291 bytes to udp/[192.168.14.68]:5060 at 07:48:32.929086: ------------------------------------------------------------------------ [592f8a31-4978-1233-90b2-d4ae52cde95f] INVITE sip:12191121212@192.168.14.68:5060 SIP/2.0 [592f8a31-4978-1233-90b2-d4ae52cde95f] Via: SIP/2.0/UDP 192.168.2.165;rport;branch=z9hG4bK4mtN7XDy2Xg7B [592f8a31-4978-1233-90b2-d4ae52cde95f] Max-Forwards: 68 [592f8a31-4978-1233-90b2-d4ae52cde95f] From: "dhrupla" <sip:14191121212@192.168.2.165>;tag=4cHc3S7N80tpm [592f8a31-4978-1233-90b2-d4ae52cde95f] To: <sip:12191121212@192.168.14.68:5060> [592f8a31-4978-1233-90b2-d4ae52cde95f] Call-ID: 592f8a31-4978-1233-90b2-d4ae52cde95f [592f8a31-4978-1233-90b2-d4ae52cde95f] CSeq: 73082792 INVITE [592f8a31-4978-1233-90b2-d4ae52cde95f] Contact: <sip:iMAX_SS@192.168.2.165:5060> [592f8a31-4978-1233-90b2-d4ae52cde95f] User-Agent: iMax_SS [592f8a31-4978-1233-90b2-d4ae52cde95f] Allow: INVITE, ACK, BYE, CANCEL, OPTIONS, MESSAGE, INFO, UPDATE, REGISTER, REFER, NOTIFY [592f8a31-4978-1233-90b2-d4ae52cde95f] Supported: precondition, path, replaces [592f8a31-4978-1233-90b2-d4ae52cde95f] Allow-Events: talk, hold, conference, refer [592f8a31-4978-1233-90b2-d4ae52cde95f] Content-Type: application/sdp [592f8a31-4978-1233-90b2-d4ae52cde95f] Content-Disposition: session [592f8a31-4978-1233-90b2-d4ae52cde95f] Content-Length: 653 [592f8a31-4978-1233-90b2-d4ae52cde95f] v=0 [592f8a31-4978-1233-90b2-d4ae52cde95f] o=iMax_SS 1426824519 1426824521 IN IP4 192.168.2.165 [592f8a31-4978-1233-90b2-d4ae52cde95f] s=iMax_SS [592f8a31-4978-1233-90b2-d4ae52cde95f] c=IN IP4 192.168.2.212 [592f8a31-4978-1233-90b2-d4ae52cde95f] t=0 0 [592f8a31-4978-1233-90b2-d4ae52cde95f] m=audio 13193 RTP/AVP 0 8 98 99 100 102 18 3 103 104 101 [592f8a31-4978-1233-90b2-d4ae52cde95f] a=rtpmap:0 PCMU/8000 [592f8a31-4978-1233-90b2-d4ae52cde95f] a=rtpmap:8 PCMA/8000 [592f8a31-4978-1233-90b2-d4ae52cde95f] a=rtpmap:98 G726-40/8000 [592f8a31-4978-1233-90b2-d4ae52cde95f] a=rtpmap:99 G726-32/8000 [592f8a31-4978-1233-90b2-d4ae52cde95f] a=rtpmap:100 G726-24/8000 [592f8a31-4978-1233-90b2-d4ae52cde95f] a=rtpmap:102 G726-16/8000 [592f8a31-4978-1233-90b2-d4ae52cde95f] a=rtpmap:18 G729/8000 [592f8a31-4978-1233-90b2-d4ae52cde95f] a=rtpmap:3 GSM/8000 [592f8a31-4978-1233-90b2-d4ae52cde95f] a=rtpmap:103 L16/8000 [592f8a31-4978-1233-90b2-d4ae52cde95f] a=rtpmap:104 iLBC/8000 [592f8a31-4978-1233-90b2-d4ae52cde95f] a=fmtp:104 mode=30 [592f8a31-4978-1233-90b2-d4ae52cde95f] a=rtpmap:101 telephone-event/8000 [592f8a31-4978-1233-90b2-d4ae52cde95f] a=fmtp:101 0-16 [592f8a31-4978-1233-90b2-d4ae52cde95f] a=silenceSupp:off - - - - [592f8a31-4978-1233-90b2-d4ae52cde95f] a=ptime:20 [592f8a31-4978-1233-90b2-d4ae52cde95f] m=audio 13193 RTP/AVP 4 101 [592f8a31-4978-1233-90b2-d4ae52cde95f] a=rtpmap:4 G723/8000 [592f8a31-4978-1233-90b2-d4ae52cde95f] a=rtpmap:101 telephone-event/8000 [592f8a31-4978-1233-90b2-d4ae52cde95f] a=fmtp:101 0-16 [592f8a31-4978-1233-90b2-d4ae52cde95f] a=silenceSupp:off - - - - [592f8a31-4978-1233-90b2-d4ae52cde95f] a=ptime:30 But Here Strange Behaviour is with G723 Codec. As you can see in SDP there is a separate "m=" Field for the G723 Codec.This SDP is wrong. But when I am using the following absolute_codec_string, I am getting the proper INVITE with proper SDP. (Removing G723 Codec) absolute_codec_string = "PCMU,PCMA,G726-40,G726-32,G726-24,G726-16,G729,GSM,L16,ILBC" 592f8a31-4978-1233-90b2-d4ae52cde95f] send 1291 bytes to udp/[192.168.14.68]:5060 at 07:48:32.929086: ------------------------------------------------------------------------ [592f8a31-4978-1233-90b2-d4ae52cde95f] INVITE sip:12191121212@192.168.14.68:5060 SIP/2.0 [592f8a31-4978-1233-90b2-d4ae52cde95f] Via: SIP/2.0/UDP 192.168.2.165;rport;branch=z9hG4bK4mtN7XDy2Xg7B [592f8a31-4978-1233-90b2-d4ae52cde95f] Max-Forwards: 68 [592f8a31-4978-1233-90b2-d4ae52cde95f] From: "dhrupla" <sip:14191121212@192.168.2.165>;tag=4cHc3S7N80tpm [592f8a31-4978-1233-90b2-d4ae52cde95f] To: <sip:12191121212@192.168.14.68:5060> [592f8a31-4978-1233-90b2-d4ae52cde95f] Call-ID: 592f8a31-4978-1233-90b2-d4ae52cde95f [592f8a31-4978-1233-90b2-d4ae52cde95f] CSeq: 73082792 INVITE [592f8a31-4978-1233-90b2-d4ae52cde95f] Contact: <sip:iMAX_SS@192.168.2.165:5060> [592f8a31-4978-1233-90b2-d4ae52cde95f] User-Agent: iMax_SS [592f8a31-4978-1233-90b2-d4ae52cde95f] Allow: INVITE, ACK, BYE, CANCEL, OPTIONS, MESSAGE, INFO, UPDATE, REGISTER, REFER, NOTIFY [592f8a31-4978-1233-90b2-d4ae52cde95f] Supported: precondition, path, replaces [592f8a31-4978-1233-90b2-d4ae52cde95f] Allow-Events: talk, hold, conference, refer [592f8a31-4978-1233-90b2-d4ae52cde95f] Content-Type: application/sdp [592f8a31-4978-1233-90b2-d4ae52cde95f] Content-Disposition: session [592f8a31-4978-1233-90b2-d4ae52cde95f] Content-Length: 653 [592f8a31-4978-1233-90b2-d4ae52cde95f] v=0 [592f8a31-4978-1233-90b2-d4ae52cde95f] o=iMax_SS 1426824519 1426824521 IN IP4 192.168.2.165 [592f8a31-4978-1233-90b2-d4ae52cde95f] s=iMax_SS [592f8a31-4978-1233-90b2-d4ae52cde95f] c=IN IP4 192.168.2.212 [592f8a31-4978-1233-90b2-d4ae52cde95f] t=0 0 [592f8a31-4978-1233-90b2-d4ae52cde95f] m=audio 13193 RTP/AVP 0 8 98 99 100 102 18 3 103 104 101 [592f8a31-4978-1233-90b2-d4ae52cde95f] a=rtpmap:0 PCMU/8000 [592f8a31-4978-1233-90b2-d4ae52cde95f] a=rtpmap:8 PCMA/8000 [592f8a31-4978-1233-90b2-d4ae52cde95f] a=rtpmap:98 G726-40/8000 [592f8a31-4978-1233-90b2-d4ae52cde95f] a=rtpmap:99 G726-32/8000 [592f8a31-4978-1233-90b2-d4ae52cde95f] a=rtpmap:100 G726-24/8000 [592f8a31-4978-1233-90b2-d4ae52cde95f] a=rtpmap:102 G726-16/8000 [592f8a31-4978-1233-90b2-d4ae52cde95f] a=rtpmap:18 G729/8000 [592f8a31-4978-1233-90b2-d4ae52cde95f] a=rtpmap:3 GSM/8000 [592f8a31-4978-1233-90b2-d4ae52cde95f] a=rtpmap:103 L16/8000 [592f8a31-4978-1233-90b2-d4ae52cde95f] a=rtpmap:104 iLBC/8000 [592f8a31-4978-1233-90b2-d4ae52cde95f] a=fmtp:104 mode=30 [592f8a31-4978-1233-90b2-d4ae52cde95f] a=rtpmap:101 telephone-event/8000 [592f8a31-4978-1233-90b2-d4ae52cde95f] a=fmtp:101 0-16 [592f8a31-4978-1233-90b2-d4ae52cde95f] a=silenceSupp:off - - - - [592f8a31-4978-1233-90b2-d4ae52cde95f] a=ptime:20 So, I am facing the problem when I am using the G723 Codec in the absolute_codec_string. Please help me to resolve this issue. I am using the freeswitch in the Proxy Mode. Thank you for your kind help Regards. Dhrupal Tilava