Subject: [Sipping] Explanation for "draft-gaoyang-sipping-session-state-criterion-01.txt"-2009/02/16-2

From: [email-masked]
Date: Mon, 16 Feb 2009 15:33:49 +0800

"draft-gaoyang-sipping-session-state-criterion-01.txt" has given out a 
precise definition of session state. And what forms a nested transaction 
is application level issue, and it is opened for evolution and extension.

Precondition forms a famous nested transaction which can have more than 
one Offer/Answer pair.
 
3GPP usage of offer/answer in PRACK/200OK or UPDATE/200OK pair to 
refine(reduce) the codec set is also a famous nested transaction which can 
have more than one Offer/Answer pair.
But we should point out that UPDATE/200OK pair changing codec set beyond 
the refine use-case MUST be treated as a new modification.

I think that considering current SIP/SDP usage in RFCs and 3GPP, the 
classification(a new modification or part of previous one) of Offer/Answer 
pairs is clear.
But if we do not adopt the precise definition of session state, it will be 
confused.

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