[SIPForum-discussion] 183 Session Progress without SDP

Ayyanar PK pkayyanar at in.com
Sat Apr 11 15:48:14 UTC 2009

 Hi Manish,I don't agree with what you said below.What you quoted from the RFC is correct, because the RFC states that a 200 OK with a SDP can be ignored if a provisional response 180 or 183 has already been received with a SDP. What you said is wrong because, there is a 183 received first without SDP and followed by another 183 with SDP. For your information there is noother 183 response from the UAS to UAC. you points stands invalid. Could you please clarify ?Best Regards,Ayyanar Original message From:Manish Aggarwal< maaggarwal at gmail.com >Date: 10 Apr 09 04:25:13Subject:Re: [SIPForumdiscussion] 183 Session Progress without SDPTo: nitin kapoor Nitin, I feel this behavior is correct, as per RFC 3261. Just for curiosity, I checked yr wireshark logs.....the Tag in "To" header is same for both the 183 repsonses... so its for the same dialog..... In rfc 3261, in section 13.2.1, it says that "The UAC MUST treat the first session description it receives as the answer, and MUST ign
 ore any session descriptions in subsequent responses to the initial INVITE." So, in your case, (1) First 183 just indicates that UAS is still processing the INVITE. And UAC doesnt need to retransmit (2) second 183, "with SDP", is equivalent to an answer. The UAC can assume this SDP to be final. (3) If any further 183 messages are received, "with or without" sdp, they should be ignored (as mentioned in the above rfc extact). I dont have any docs.....just based on my understanding...... Hope it helps Thanks Manish On Thu, Apr 9, 2009 at 5:10 PM, nitin kapoorwrote: Hello Manish,Thanks for the response.Do you have any docs where i can read something about this topic to clear my doubts. Do you think this is the correct behavior.ThanksNitin Kapoor 2009/4/9 Manish Aggarwal Multiple provisional responses is allowed as per the protocol spec. This can be used to create an early dialogue. A UAS will send this, when its taking long time to process INVITE (and before sending 200 OK). Hav
 e heard of this behavior before though. ManishOn Thu, Apr 9, 2009 at 12:26 PM, nitin kapoorwrote:Dear All,We are facing one problem where we are getting two 183 session for 1 INVITE. UAC sending the INVITE to Switch and switch has forwarded the same invite to UAS. Then UAS first send the 183 Session progress without SDP and after 2 Sec its sends the another 183 Session Progress with SDP which is something i am not able to understand.1) Can you please tell me on which cases UAS sends the two 183 Session progress like this.( with SDP & without SDP)?2) Is this the correct behaviour?I checked this on RFC3261 and another sip pdf but unable to search it. Please find the attached Traces.ThanksNitin KapoorThis is the SIP Forum discussion mailing listTO UNSUBSCRIBE, or edit your delivery options, please visit http://sipforum.org/mailman/listinfo/discussion Post to the list at discussion at sipforum.org
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