JSEP-01: SDP_PRANSWER and FEDEX use-case

Hi,

Section 6.1.4 of jsep-01 says:

        "SDP_PRANSWER indicates that a description should be parsed as an
        answer, but not a final answer, and so should not result in the
        starting of media transmission. A description used as a SDP_PRANSWER
        may be applied as a response to a SDP_OFFER, or an update to a
        previously sent SDP_PRANSWER."


Section 7.6 shows a SIP early media (FEDEX) use-case, where an SDP answer received in a SIP 18x response is provided to the browser as a SDP_PRANSWER.


Q1: Since SDP_PRANSWER is not supposed to start media transmission, how will the use-case work? As far as I know, media transmission is needed for the FEDEX use-case.

Q2: The draft doesn't really specify what SDP_PRANSWER is used for. I understand that it means that a "final" answer may be provided later, but it doesn't really say what the a browser would do with an SDP_PRANSWER - especially since it doesn't seem to enable media.

Q3: Assuming we would allow multiple SDP_ANSWER (see separate thread), is there a need for SDP_PRANSWER?

Regards,

Christer