I noticed that recent freeswitch versions could send SDP with 2 m=audio lines. Per RFC 3388, the behavior is undefined this case. I don't know how to reproduce the problem, I see such packets coming from my customers. Here is an example: INVITE sip:xxxxxxxxxxxx@sip.callwithus.com SIP/2.0 ... User-Agent: FreeSWITCH-mod_sofia/1.0.head-git-eeeaf41 2012-02-10 17-27-50 -0600 .... v=0 o=FreeSWITCH 1329167961 1329167962 IN IP4 xx.xx.xx.xx s=FreeSWITCH c=IN IP4 xx.xx.xx.xx t=0 0 m=audio 24598 RTP/AVP 0 101 13 a=rtpmap:101 telephone-event/8000 a=fmtp:101 0-16 a=ptime:30 m=audio 24598 RTP/AVP 98 0 8 3 101 13 a=rtpmap:98 SILK/8000 a=fmtp:98 useinbandfec=1; usedtx=0 a=rtpmap:101 telephone-event/8000 a=fmtp:101 0-16 a=ptime:20 Hmm, I just realized that this SDP is buggy - 2 audio streams on the same port, with common codecs, but with different ptime :-)