Orignal description:
And there is a more situation: if the precondition notification with the orignal precondition OK and add another new precondition(it is legitimate, but unordinary). As the precondition of the session is still exist, the session is still in suspending state. And the one is precondition notification.
Chapter 8 of RFC3312:
When a UAS, acting as an answerer, cannot or is not willing to meet the preconditions in the offer, it SHOULD reject the offer by returning a 580 (Precondition-Failure) response.
So, the precondition can be rejected for wishes of user or UA. So, modification of precondition itself(not precondition satisfied state) MUST be treated as a new modification. And it obeys the natural demand of one side to reject the other side's Offer with too much precondition. :)
As a new modification, the session state would be judge by the way as other new modification.
So the original description in the mail to Christer Holmberg is not correct. I apologize for that.
Gaoyang
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