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List:       sip-implementors
Subject:    [Sip-implementors] Clarification on scenario with CSeq reordering
From:       "Jeroen van Bemmel" <jbemmel () zonnet ! nl>
Date:       2005-07-30 22:55:58
Message-ID: 003201c59559$d9e1a980$6502a8c0 () BEMBUSTER
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All,

Is the following scenario possible?

UAC A establishes a dialog by INVITING UAC B, 100, 180, 200, ACK as usual.
- UAC A sends a re-INVITE (CSeq 2)
- UAC A sends another request UPDATE (CSeq 3) [ "a UA MAY initiate a regular 
transaction while an INVITE transaction is in progress" ]
- UAC B receives the re-INVITE, sends a provisional response 180 ringing
- UAC A then decides to CANCEL (CSeq 2) the re-INVITE
- UAC B receives UPDATE (CSeq 3)
- UAC B receives CANCEL (CSeq 2), sends 500 since it is out of order

I am trying to get a clarification on section 12.2.2, and was wondering if 
an exception should be made for CANCEL and ACK since they carry the sequence 
number of the request they refer to, which is lower than the most recent one 
in case any new requests are sent in between the original request and the 
CANCEL or ACK

Regards,

jeroen 


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