[SIPForum-discussion] 183 Session Progress without SDP

Vivek Batra Vivek.Batra at matrixtelesol.com
Fri Apr 10 06:32:51 UTC 2009

Although multiple provisional responses are allowed, 183 Session Progress is
used to connect early media. How this will be achieved without having SDP in
183 Session Progress? So, no use to send 183 Session Progress without SDP.
Application can be understood when 180 Ringing (w/o SDP) is sent followed by
183 Session Progress (with SDP). But, I don't see the real application of
sending 183 Session Progress (w/o SDP) followed by 183 Session Progress
(with SDP), except might be allowed by standard. 
Best Regards,
Vivek Batra


From: discussion-bounces at sipforum.org
[mailto:discussion-bounces at sipforum.org] On Behalf Of Manish Aggarwal
Sent: Friday, April 10, 2009 12:53 AM
To: nitin kapoor
Cc: discussion
Subject: Re: [SIPForum-discussion] 183 Session Progress without SDP

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.

On Thu, Apr 9, 2009 at 12:26 PM, nitin kapoor <nitinkapoorr at gmail.com>

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.

Nitin Kapoor

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