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[rtcweb] "pranswer" be applied as an update to a previously sent "answer"?

"Lijing (Jessie)" <lijing80@huawei.com> Wed, 20 November 2013 11:22 UTC

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From: "Lijing (Jessie)" <lijing80@huawei.com>
To: "justin@uberti.name" <justin@uberti.name>
Thread-Topic: "pranswer" be applied as an update to a previously sent "answer"?
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Subject: [rtcweb] "pranswer" be applied as an update to a previously sent "answer"?
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draft-ietf-rtcweb-jsep-05 -----Section 4.1.3 says:

"pranswer" indicates that a description should be parsed as an
   answer, but not a final answer, and so should not result in the
   freeing of allocated resources.  It may result in the start of media
   transmission, if the answer does not specify an inactive media
   direction.  A description used as a "pranswer" may be applied as a
   response to an "offer", or an update to a previously sent "answer".

How can a pranswer be applied as an update to a previously sent answer?  I am not sure what's the corresponding scenario.
>From the state machine perspective, when answer is received, it enters the stable state. At this point, the state machine can not directly jump to local pranswer or remote pranswer state.

My two cents: May be it needs more description or correction here.


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