In Section 6.3 of the 100-rel draft's 03 version, it is said -

The UAS MUST NOT send a second reliable provisional
   response until the first is acknowledged. After the first, it is
   RECOMMENDED that the UAS not send an additional reliable provisional
   response until the previous is acknowledged.


It is also said in the same section -

A UAS MUST NOT send new
   reliable provisional responses (as opposed to retransmissions of
   outstanding ones) after sending a final response to a request.


Suppose a UAS receives the following in rapid succession (or any other valid
sequence of provisionals followed by 200)

182 2 in Queue
182 1 in Queue
183 Session Progress
180 Ringing
200 OK

The 200 may get sent even before the PRACK to the first one is received. In
that case, (based on the above extracts from the draft) the other
provisional responses MUST not be sent. However, there may be useful
information in the attachments (eg. ISUP INFO for SIP-T)  that should be
conveyed reliably but cannot be sent.

Would it be better to send all pending provisionals unreliably before
transmitting the 200? What is the recommendation?






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