Re: [rtcweb] Symmetric RTP and uni-directional media streams

Bernard Aboba <> Thu, 01 September 2011 14:34 UTC

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Subject: Re: [rtcweb] Symmetric RTP and uni-directional media streams
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I think Christer's question related to the following text from the W3C WEBRTC editor's draft ( Section 4:

All streams represented by MediaStream objects must be
  marked as "sendonly" by the peer that initially adds the stream to
  the session. The PeerConnection API does not support
  bidirectional ("sendrecv") audio or video media streams. [SDPOFFERANSWER]

Date: Thu, 1 Sep 2011 13:30:55 +0200
Subject: Re: [rtcweb] Symmetric RTP and uni-directional media streams


    On 09/01/11 13:23, Christer Holmberg wrote:
        There has been
            much talk about the usage of symmetric RTP. Also,
            draft-perkins-rtcweb-rtp-usage suggests that symmetric RTP
            is required.
        However, the
            PeerConnection API currently only supports the establishment
            of uni-directional streams, so for a single two way
            communication one needs to create two separate
            uni-directional streams.
        So, I assume
            that one requirement from RTCWEB to W3C will be to add
            support of the establishment of bi-directional streams to
            the PeerConnection API.
    To be precise:


    I think (and we're implementing) that between two PeerConnections,
    there will be a small number of *RTP sessions*  (ideally one). These
    will be bidirectional.


    These will be used for transporting any number of *MediaStreams* (a
    WEBRTC API concept), each of which corresponds to a CNAME (RTP
    protocol concept). These are unidirectional.


    So the right answer is "yes" and "no", as far as I can see.

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