Subject: [sipcore] Why "rollback" and how "rollback" // New revision of the re-INVITE handling draft

From: [email-masked]
Date: Thu, 9 Jul 2009 16:56:05 +0800

[as individual]

Why "rollback"?
Choose the session state is the first step. And the reason is:
1. Obey the original concept of RFC3261;
2. It is the intuitionistic(user point of view) requirement for rejecting 
session modification.

How "rollback"?
Choose the solution of how to reach the state is the second step:
There are more than one solution for this. Widely discussed solutions are:
1. draft-gaoyang-sipping-session-state-criterion-03
2. draft-camarillo-sipcore-reinvite-00 

"draft-gaoyang-sipping-session-state-criterion-03" classify session 
modifications into different categories and specify different rules for 
different categories. This proposal has same merits:
1. Has no violation to current RFCs;
2. Has no racing condition problem.
But Gonzalo pointed out a problem(I remember Paul said something like 
this, but not shocked me at that time): Impossible to understand the 
current state by just looking the call flow; details about the messages 
would be needed. Though we can avoid it by BCP, it is really a problem in 
theory which changes the charts' style for our engineers.

So, I support "draft-camarillo-sipcore-reinvite-00" now. And we really 
need the regulation to making equipment interworking about this problem 
exercisable.

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