Re: [MMUSIC] What is an m-line?
Colin Perkins <csp@csperkins.org> Wed, 15 May 2013 11:03 UTC
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From: Colin Perkins <csp@csperkins.org>
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Subject: Re: [MMUSIC] What is an m-line?
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On 13 May 2013, at 19:42, Martin Thomson wrote: > We've had a great deal of discussion about plan A and B and the > various interactions of these proposals with bundling. But I still > don't get a good sense that there is a working consensus on what an > m-line actually represents. > > I think that we've each reached our own conclusions, but they > definitely are not consistent. We need a well-understood semantic for > m-lines if we have any chance of resolving these issues; Plan A/B > being only the first RTCWEB problem to address. > > RFC 4566 is helpfully devoid of detail, so we are free to come up with > any interpretation we choose. Here are the ones that I have seen: > > 1. an m-line represents a single RTP session > (or at least the part of the session that touches the client) > This appears to be consistent with the Plan B approach This is closest to my understanding, although an RTP session is defined by a shared SSRC space that can span multiple transport connections, so I don't think it's quite right. Perhaps "an m-line refers to one transport endpoint of a single RTP session"? (For example, in a simple two-party voice-only call with RTCP there are distinct m-lines, with different transport endpoints, in the offer and the answer. But, since there is a shared SSRC space across the sending and receiving RTP flows - which there has to be for RTCP to work - you have one RTP session.) > 2. an m-line represents the set of RTP streams that decode into a > single rendering, including layers, simulcast and FEC > > 3. an m-line represents a single RTP stream; multiple m-lines might > be required to obtain a single rendering if it uses layers, simulcast, > FEC or FID groupings > This appears to be consistent with the Plan A approach > > In the first instance, an m-line can be multiple "things". In the > latter two cases, an m-line is consistently one "thing" (or part > thereof). > > The first interpretation has a natural advantage in terms of signaling > economy and natural bundling. The latter interpretations seem to have > advantages in dealing with call transfer and SSRC renumbering. > > So, which is correct? > _______________________________________________ > mmusic mailing list > mmusic@ietf.org > https://www.ietf.org/mailman/listinfo/mmusic -- Colin Perkins http://csperkins.org/
- Re: [MMUSIC] What is an m-line? Paul Kyzivat
- Re: [MMUSIC] What is an m-line? Colin Perkins
- Re: [MMUSIC] What is an m-line? Bernard Aboba
- [MMUSIC] What is an m-line? Martin Thomson
- Re: [MMUSIC] What is an m-line? Paul Kyzivat
- Re: [MMUSIC] What is an m-line? Bernard Aboba
- Re: [MMUSIC] What is an m-line? Jonathan Lennox
- Re: [MMUSIC] What is an m-line? Martin Thomson
- Re: [MMUSIC] What is an m-line? Martin Thomson
- Re: [MMUSIC] What is an m-line? Cullen Jennings (fluffy)
- Re: [MMUSIC] What is an m-line? Martin Thomson
- Re: [MMUSIC] What is an m-line? Colin Perkins
- Re: [MMUSIC] What is an m-line? Kevin Dempsey
- Re: [MMUSIC] What is an m-line? Martin Thomson
- Re: [MMUSIC] What is an m-line? Colin Perkins
- Re: [MMUSIC] What is an m-line? Harald Alvestrand
- Re: [MMUSIC] What is an m-line? Bernard Aboba
- Re: [MMUSIC] What is an m-line? Martin Thomson
- Re: [MMUSIC] What is an m-line? Emil Ivov
- Re: [MMUSIC] What is an m-line? Martin Thomson
- Re: [MMUSIC] What is an m-line? Emil Ivov
- Re: [MMUSIC] What is an m-line? Martin Thomson
- Re: [MMUSIC] What is an m-line? Emil Ivov
- Re: [MMUSIC] What is an m-line? Paul Kyzivat
- Re: [MMUSIC] What is an m-line? Paul Kyzivat
- Re: [MMUSIC] What is an m-line? Paul Kyzivat
- Re: [MMUSIC] What is an m-line? Harald Alvestrand
- Re: [MMUSIC] What is an m-line? Paul Kyzivat
- Re: [MMUSIC] What is an m-line? Suhas Nandakumar