[SIPForum-discussion] 183 Session Progress without SDP

Manish Aggarwal maaggarwal at gmail.com
Thu Apr 9 22:55:13 UTC 2009


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 ignore 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 re-transmit
(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


On Thu, Apr 9, 2009 at 5:10 PM, nitin kapoor <nitinkapoorr at gmail.com> wrote:

> 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.
> Thanks
> Nitin Kapoor
> 2009/4/9 Manish Aggarwal <maaggarwal at gmail.com>
>> 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).
>> Have heard of this behavior before though.
>> -Manish
>>   On Thu, Apr 9, 2009 at 12:26 PM, nitin kapoor <nitinkapoorr at gmail.com>wrote:
>>>  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.
>>> Thanks
>>> Nitin Kapoor
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