Sorry Christina to hijack
Paul D.Smith wrote:
Christina,
See RFC3261, section 14.2, page 89. To quote...
If a UAS generates a 2xx response and never receives an ACK, it SHOULD generate a BYE to terminate the dialog.
So UA Y should have BYEd the session.
No. In step 9 a retransmission is received, meaning that it was less than 64*T1 seconds after sending the first 200. Section 13.3.1 says "If the server retransmits the 2xx response for 64*T1 seconds without receiving an ACK, the dialog is confirmed, but the session SHOULD be terminated. This is accomplished with a BYE..."
It is possible that for some reason the BYE never reached X in which case Y believes the session is gone. For the second re-INVITE I would therefore have expected a 481 not a 400.
So to answer your questions, in step 7, the UA (X) can reINVITE because it has no way of knowing that the ACK didn't reach UA Y.
In step 8, I would have expected a 481 error, but a 400 might
occur - I would need to see the actual messages exchanged to comment further.
FYI, if the UA (Y) believed that the reINVITE of step 4 were outstanding, it should have sent a 491 response to the reINVITE of step 7 (as per RFC3261, 14.2).
Paul D.Smith
Network Protocols Group Data Connection Ltd (DCL)
Tel: +44 20 8366 1177 Email: [EMAIL PROTECTED] Fax: +44 20 8363 1039 Web: http://www.dataconnection.com
-----Original Message----- From: [EMAIL PROTECTED] [mailto:[EMAIL PROTECTED] Behalf Of Christina Zhao Sent: 15 July 2004 17:31 To: SIP (E-mail) Subject: [Sip-implementors] question for re-re-invite
I met a problem when I study the SIP Spec. Can anyone give me his/her
advice for that? Thanks a lot.
The scenario is:
1. UA Y invited UA X.
2. UA X 200ed UA Y.
3. UA Y acked UA X. (SIP Session is established)
4. UA X re-invited UA Y. 5. UA Y 200ed UA X. 6. UA X acked UA Y. (It seems that UA Y doesn't get it because UA X receives retransmission of 200 in step 9)
7. UA X re-invited UA Y AGAIN (Is it valid?) 8. UA Y 400ed UA X. (Is it valid?)
9. UA X received retransmission of step 5.
Q1: For UA X, we think step 7 is valid because the first re-invite transaction is already over, is that true? Q2: We are not very clear about step 8. For UA Y, the 2nd re-invite comes before it receives ack of 1st re-invite. What should UA Y do?
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