[SIPForum-discussion] INVITE without SDP and 1XX provisional answer with SDP

Jean-Sébastien Decubber js.decubber at gmail.com
Thu May 22 08:31:15 UTC 2008

Dear All,

I am currently doing some interworking test between two CPE. For a very
specific scenario I reach the following call flow:

1) User A sends an INVITE without SDP to user B.
2) User B answers with a 183 session progress with SDP.

So user B wants to send early media, but at this stage it doesn't where to
send it because user A doesn't send any SDP in the invite.
I know that PRACK mechanism can be used for this kind of scenario. But I
would like to know if there is any RFC defining scenario?
If the user A doesn't put the 100 rel tag in the INVITE (meaning that it
doesn't support PRACK), is user B allowed to send this 183 SP with SDP?

 Is there any "official way" to support this scenario (so I can try to know
who is the guilty one)??

Thanks and regards,
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