I have re-formulated an earlier question with a better explanation (I hope!)
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
2XX/3XX/ 4XX/5XX/6XX
The final response may be available to be 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, with cause code) that should be
conveyed reliably but cannot be sent.
If the final response is 200 OK, the attachment in that response is adequate
and there should be no loss of information by dropping the provisional
responses. But if the final response is a failure response, the attachment
in an earlier 183 will have IEs that are required, for example, to
correctly interpret the cause of the call failure.
Should we queue up a non-200 final response to wait for the first PRACK?
Of course, if the call is going to fail, this should not be a issue.
Any recommendations ?
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