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OfferToReceive in CreateAnswer

From: Harald Alvestrand <harald@alvestrand.no>
Date: Fri, 26 Oct 2012 13:47:11 +0200
Message-ID: <508A783F.2080006@alvestrand.no>
To: "public-webrtc@w3.org" <public-webrtc@w3.org>
Wearing my implementor's hat, reporting on a discussion:

The text in section 11.1 about OfferToReceiveAudio and 
OfferToReceiveVideo talks about offers, but doesn't say what should be 
done with answers. If the language was interpreted exactly as it stands, 
the result of doing a CreateAnswer without adding any streams would be 
to create an SDP that rejected the Audio and Video m-lines - which 
doesn't make much sense.

A reasonable interpretation should be this (all refer to the responding 
RTCPeerConnection):

- When no OfferToReceive* is present, and no streams are added, all m= 
lines from sender are accepted. (Query: should they be accepted in 
a=recvonly mode?)

- When OfferToReceive* is nandatory false, and no streams are added, the 
corresponding m= line is rejected (by setting the port number to 0).

- I don't think we can add m= lines in an answer, so when the incoming 
offer has no video line, and the OfferToReceiveVideo is true, the 
answerer fires negotiationneeded immediately after returning to the 
no-outstanding-offer state, so that the answerer can offer an upgrade to 
add video.

Does this make sense? If so, can it be added?

               Harald
Received on Friday, 26 October 2012 11:47:40 UTC

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