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Adam’s m = line Musings

Adam’s m = line Musings. draft-roach-mmusic-mlines-00 RTCWEB Interim Boston, MA February 5 th , 2013. Three Proposed Approaches. Approach 1a: One m= section per media type, regardless of how many streams of that type in the session Approach 1b: One m= section per session (MMT)

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Adam’s m = line Musings

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  1. Adam’s m= line Musings draft-roach-mmusic-mlines-00 RTCWEB Interim Boston, MA February 5th, 2013

  2. Three Proposed Approaches • Approach 1a: One m= section per media type, regardless of how many streams of that type in the session • Approach 1b: One m= section per session (MMT) • Approach 2: One m= section per media stream

  3. Codec Selection • Handling of preferences in RFC3264 currently assumes one-stream-per-m-section model • This requires fix-up for approaches 1a and 1b (or ambiguity and loss of control) • Favors approach 2

  4. Port Number Handling • SDP syntax does not natively support bundling more than one m= section into a single session (port # is mandatory). • For solutions 1a and 2, we need to choose “the lesser of two evils”: • Indicating the same port in all lines trips up legacy use • Indicating different ports (some bogus) in each line trips up some SBCs • Favors approach 1b

  5. Attribute Handling • Since attributes can roughly apply to either sessions or to streams, creating a distinction requires updates to attribute handling • Approaches 1a and 1b can use RFC5576 for stream-level attributes • Approaches 1a and 2 can indicate transport-level attributes in all relevant m= sections • Because 1a must address both situations, it is more complicated than the either two.

  6. Unknown Unknowns • Problems such as the codec selection problem are yet to be identified for the general case. • Addressing these issues in the future is easiest if we have the most granular control surface possible. • This also makes future extensions more compatible with non-RTCWEB SDP use • This supports selection of the most granular control surface, which is alternative 2.

  7. Problems with all solutions • Offerer and answerer needing different number of streams • Attribute bidirectionality • Implementation complexity

  8. Approach Summary

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