[SIPForum-discussion] Reg: SDP offer

Ayyanar PK pkayyanar at in.com
Thu Apr 9 13:45:07 UTC 2009

 Hi Prem,I have never seen such a SDP.The intention is to send fax over T.38 or G.711.I ask this because, I can see Image as well as a ReINVITE with only G.711 code in ReINVITE's SDP.Also in 180 Ringing the SDP has both audio as well as image. What is the need or purpose to send T.38 information in the initial negotiation even if it is fax call. I dont understand this negotiation. Can you elobrate on this ? or can somebody elobrate on this ?Regards,Ayyanar Original message From:prem ranjan< prem.behera at gmail.com >Date: 08 Apr 09 16:34:52Subject:[SIPForumdiscussion] Reg: SDP offerTo: discussion at sipforum.orgHi,I have the following scenario:A calls BA sends INVITE with the following SDP:v=0o=780 409699 409699 IN IP4 192.168.0..20s=c=IN IP4 0m=audio 41270 RTP/AVP 8 18 4 96 a=rtpmap:96 telephoneevent/8000a=ptime:20a=SilenceSupp:offa=fmtp:96 015a=nortpproxy:yesB answers the following SDP in 180 Ringing:v=0o= 38000001 1239174750 IN IP4 s=SDP Datac=IN I
 P4 0m=audio 18990 RTP/AVP 8 96a=rtpmap:96 TELEPHONEEVENT/8000a=ptime:20a=sqn:0a=cdsc:1 image udptl t38a=cpar: a=T38FaxVersion:0a=cpar: a=T38MaxBitRate:14400 a=cpar: a=T38FaxRateManagement:transferredTCFa=cpar: a=T38FaxMaxBuffer:280a=cpar: a=T38FaxMaxDatagram:260a=cpar: a=T38FaxUdpEC:t38UDPRedundancyAfter this Call is successful.Now B wants to send a FAX. For this it creates a ReInvite with the following SDP: v=0o= 38000001 1239174761 IN IP4 Datac=IN IP4 0m=audio 0 RTP/AVP 8a=ptime:10m=image 33815 udptl t38a=T38FaxVersion:0 a=T38MaxBitRate:14400a=T38FaxRateManagement:transferredTCFa=T38FaxMaxBuffer:1800a=T38FaxMaxDatagram:260a=T38FaxUdpEC:t38UDPRedundancyNow my question is, can we have the value "Zero" in the audio port. Is this RFC compliant??? Kind Regards,Prem Ranjan Behra
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