Victor Paulsamy wrote:
> Paul,
>
>> -> INVITE w/offer1
>> <- 18x (reliable) w/answer1
>> -> PRACK w/offer2
>> <- 200 PRACK w/answer2
>> <- 200 INVITE w/answer1
>> -> ACK
>>
>> The above is a legal flow. The caller *should not* end up using
>> answer1.
>
>
> How do you say that this is a legal flow when "200 INVITE w/answer1"
> broke the "consistent" view of O/A across UAC & UAS -- the primary goal
> of O/A exchange?
This is a legal flow because the requirement is that if there is sdp in
both a provisional and the final response for the INVITE, then they must
be the same. This is true whether the provisional is reliable or not.
If the provisional is not reliable, then the sdp must also be in the
200. If the provisional is reliable, then the 200 preferably doesn't
have sdp at all, but if it does, then it must be the same as was in the
provisional.
In the above, there have been two offer/answer exchanges in the
*dialog*, with one of them in the INVITE transaction, the other in the
PRACK transaction. The SDP in the 200 must not be considered to be a
change - it really isn't either an offer or an answer, it is just
something to be ignored.
Paul
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