[SIPForum-discussion] Reg: SDP offer

Ayyanar PK pkayyanar at in.com
Sat Apr 11 15:20:44 UTC 2009

 Hi Tomasz,Can you relate the information you said below with the SDP descriptions gives by the poster. I mean can you say which is the new media stream here and which is existing and finally which will be considered for the negotiation. What I understand is audio line is the existing and it has port zero, hence this will be used for negotiation. Am I right ?Did you see this info by Nils Ohlmeier Yes port zero is absolutely legal. And it is even required, because itis the only way how to reject mlines if there are multiple of them.Note that the reINVITE contains two mlines. So the sender tells youthat he does not want to do audio any longer, but wants to switch toimage (T38 in this case) in this case.I think both of you are not saying the samething. Could you clarify your part ?Best Regards,Ayyanar Original message From:Tomasz Zieleniewski< tzieleniewski at gmail.com >Date: 09 Apr 09 18:39:35Subject:Re: [SIPForumdiscussion] Reg: SDP offerTo: prem ranjan Hi,Yes this RFC compliant
 . Usage of zero port has the following reason. Generally any new media streams are created by new additional media descriptions in the SDP. New stream are added below the existing ones. But in the case when one side want's to utilize and allready existing stream it sets its port to zero. Then any new media descriptions which replace the previous ones must appear below any existing media sections.Kind regards Tomasz Zieleniewski2009/4/8 prem ranjan : > Hi, > I have the following scenario: > A calls B > A sends INVITE with the following SDP: > > v=0 > o=780 409699 409699 IN IP4 > s= > c=IN IP4 > t=0 0 > m=audio 41270 RTP/AVP 8 18 4 96 > a=rtpmap:96 telephoneevent/8000 > a=ptime:20 > a=SilenceSupp:off > a=fmtp:96 015 > a=nortpproxy:yes > > > B answers the following SDP in 180 Ringing: > > v=0 > o= 38000001 1239174750 IN IP4 > s=SDP Data > c=IN IP4 > t=0 0 > m=audio 18990 RTP/AVP 8 96 > a=rtpmap:96 TELEPHONEEVENT/8000 > a=pt
 ime:20 > a=sqn:0 > a=cdsc:1 image udptl t38 > a=cpar: a=T38FaxVersion:0 > a=cpar: a=T38MaxBitRate:14400 > a=cpar: a=T38FaxRateManagement:transferredTCF > a=cpar: a=T38FaxMaxBuffer:280 > a=cpar: a=T38FaxMaxDatagram:260 > a=cpar: a=T38FaxUdpEC:t38UDPRedundancy > > After this Call is successful. > Now B wants to send a FAX. For this it creates a ReInvite with the > following SDP: > > v=0 > o= 38000001 1239174761 IN IP4 > s=SDP Data > c=IN IP4 > t=0 0 > m=audio 0 RTP/AVP 8 > a=ptime:10 > m=image 33815 udptl t38 > a=T38FaxVersion:0 > a=T38MaxBitRate:14400 > a=T38FaxRateManagement:transferredTCF > a=T38FaxMaxBuffer:1800 > a=T38FaxMaxDatagram:260 > a=T38FaxUdpEC:t38UDPRedundancy > > Now my question is, can we have the value "Zero" in the audio port. Is this > RFC compliant??? > > Kind Regards, > Prem Ranjan Behra >  > This is the SIP Forum discussion mailing list > TO UNSUBSCRIBE, or edit your delivery options, please visit > http://sipforum.org/mailman/
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