Re: [rtcweb] SDP is not suitable for WebRTC
Silvia Pfeiffer <silviapfeiffer1@gmail.com> Mon, 29 July 2013 22:53 UTC
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From: Silvia Pfeiffer <silviapfeiffer1@gmail.com>
Date: Tue, 30 Jul 2013 08:52:51 +1000
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To: Iñaki Baz Castillo <ibc@aliax.net>
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Cc: "rtcweb@ietf.org" <rtcweb@ietf.org>, "public-webrtc@w3.org" <public-webrtc@w3.org>
Subject: Re: [rtcweb] SDP is not suitable for WebRTC
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On Tue, Jul 30, 2013 at 3:31 AM, Iñaki Baz Castillo <ibc@aliax.net> wrote: > Hi, I initiated a thread [*] about Plan-Unified and multiple m lines, > but it was moved to MMUSIC maillist (don't know why since it is about > WebRTC applications design): > > http://www.ietf.org/mail-archive/web/mmusic/current/msg11966.html > > Sorry for the cross-posting but at this point I'm a bit lost and do > not know which is the appropriate group for my concern. > > > > So my concern is: > > > - Web application with a SIP over WebSocket client running in the web. > > - The web user is provided with a conference SIP URI in which there > are *already* 8 participants (5 of them emitting audio and video and 3 > just emitting audio). > > - The user calls, from his webphone, to the given URI to join the conference. > > > > Let's imagine that the JS app knows the number of participant in the conference. > Let's imagine my browser have mic and webcam. > > > > QUESTION: > > How can my browser join the conference without requiring SDP > renegotiation from the server and, at the same time, being able to > send audio/video and receive audio/video from others (different tracks > / m=lines)? > > > > > "SOLUTIONS": > > > > 1) > > I tell my browser to generate a SDP offer with: > > - 1 send/receive m=audio line. > - 7 recvonly m=audio line. > - 1 send/only m=video line. > - 4 recvonly m=video line. > > (Obviously this is a joke) Since you seem to be doing a full mesh and you seem to be wanting to receive from everyone and be able to talk back to everyone, wouldn't this need to be 8 different SDP offers in a full mesh network rather than one SDP offer with 13 different m-lines? I don't follow how each of the recipients would pick the right m-line for themselves... > 2) > > SDP seems to allow that the offer and the answer have different number > of m lines (I'm not aware of that but I believe that SDP can do > "everything"). So my browser generates a SDP offer with 1 m=audio line > and 1 m=video line, and the server replies with 8 m=audio lines and 4 > m=video lines. > > Will my browser understand such a SDP answer with more m lines than > its generated offer? I assume NOT. I'm don't understand SDP, but logic would tell me that it would send a single SDP offer with its own capabilities to each of the other 8 participants: m=audio send/receive (not sure if it also needs m=video, since it's not a video capable device IIUC) > 3) > > My browser generates a SDP offer with 1 m=audio line and 1 m=video > line and the server too. And later the server sends re-INVITE with all > the m lines. > > Oppss, SDP renegotiation... Yes, I would expect a negotiation to happen between each of the 8 current participants and the one new participant individually. It would end up in 8 O/A negotiations that should all end up with 5 m=audio send/receive and 3 m=audio receive-only (from the POV of the webphone. I'm taking a stab at this because I want to understand more about how it works, but I actually have no idea if I am correct. Please, somebody with SDP knowlege, clarify how this would actually work. I, too, am very curious. Thanks, Silvia.
- [rtcweb] SDP is not suitable for WebRTC Iñaki Baz Castillo
- Re: [rtcweb] SDP is not suitable for WebRTC piranna@gmail.com
- Re: [rtcweb] SDP is not suitable for WebRTC Bossiel thioriguel
- Re: [rtcweb] SDP is not suitable for WebRTC Iñaki Baz Castillo
- Re: [rtcweb] SDP is not suitable for WebRTC Silvia Pfeiffer
- Re: [rtcweb] SDP is not suitable for WebRTC Ron
- Re: [rtcweb] SDP is not suitable for WebRTC Christer Holmberg
- Re: [rtcweb] SDP is not suitable for WebRTC Iñaki Baz Castillo
- Re: [rtcweb] SDP is not suitable for WebRTC Iñaki Baz Castillo
- Re: [rtcweb] SDP is not suitable for WebRTC Christer Holmberg
- Re: [rtcweb] SDP is not suitable for WebRTC Iñaki Baz Castillo
- Re: [rtcweb] SDP is not suitable for WebRTC (UNCL… Roy, Radhika R CIV USARMY (US)