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RTP Media Congestion Avoidance Techniques (Active WG)
Tsv Area: Mirja Kühlewind, Spencer Dawkins | 2012-Sep-25 —  
Chairs
 
 
 


IETF-99 rmcat minutes

Session 2017-07-19 0930-1200: Karlin III - Audio stream - rmcat chatroom

Minutes

minutes-99-rmcat-00 minutes



          RMCAT Working Group, IETF 99
          ============================
          
             Reported based on notes taken by Alan Ford and Colin Perkins.
          
          
          ## Working Group Status
          
             The chairs reviewed the agenda and status of the working group
             documents. The requirements (draft-ietf-rmcat-cc-requirements-09)
             remain in the RFC Editor queue, blocked on a missing normative
             reference.
          
             The group has three candidate congestion control algorithms and two
             related drafts:
          
             - draft-ietf-rmcat-coupled-cc-06 has been submitted to the IESG
             - draft-ietf-rmcat-sbd-08 has been updated to address review comments,
               and is now ready for submission to the IESG
             - draft-ietf-rmcat-scream-cc-09 is ready for submission to the IESG
             - draft-ietf-rmcat-nada-04 is waiting for an update from the authors to
               address working group last call comments, and is expected to be ready
               for submission to the IESG soon
             - draft-ietf-rmcat-gcc-02 is waiting for an update from the authors
          
             The group also has several drafts relating to evaluation of candidate
             algorithms, test criteria, and the like:
          
             - draft-ietf-rmcat-eval-test-05 is ready for working group last call
             - draft-ietf-rmcat-eval-criteria-06 is waiting resolution of an open
               issue around the choice of TCP model; the intent is to send it for
               working group last call along with draft-ietf-rmcat-eval-test-05
               once this has been done
             - draft-ietf-rmcat-wireless-tests-04 has no known open issues, but
               reviews and implementation experience are needed.
             - draft-ietf-rmcat-video-traffic-model-03  has been updated, and needs
               review. The authors believe this is ready for working group last
               call.
          
             The codec interactions (draft-ietf-rmcat-cc-codec-interactions-02) and
             framework (draft-zhu-rmcat-framework-00) drafts have expired. The next
             steps for these were discussed later in the meeting.
          
             The feedback format (draft-dt-rmcat-feedback-message-03) was updated,
             but the feedback timing draft (draft-ietf-rmcat-rtp-cc-feedback-03) has
             expired. These were discussed in the design team status update.
          
          
          
          ## RMCAT feedback design team status update
          
             Zahed Sarker gave a brief review of the design team activities
             since the
             last meeting, and passed over to Colin Perkins who presented an
             analysis
             of the overheads of different congestion feedback mechanisms.
          
             Colin compared the performance of the congestion feedback mechanism
             from
             draft-holmer-rmcat-transport-wide-cc-extensions-01 with the design team
             proposal (draft-dt-rmcat-feedback-message-02), for VoIP and two-party
             video conferencing scenarios. Details are in the slides, but in summary
             the mechanism in transport-wide-cc-extensions has lower overhead than
             the design team proposal for the VoIP scenario, but doesn't provide ECN
             feedback. For the video conferencing scenario, the design team proposal
             generally, but not always, has slightly lower overhead -- and it also
             provides ECN feedback (the results for the video conferencing scenario
             depend heavily on the loss patterns and the number of RTP packets sent
             per report).
          
             Zahed summarised the conclusion of the design team: it's not believed
             the benefits of further optimising draft-dt-rmcat-feedback-message-02
             are worth the complexity.
          
             There were a number of questions for clarification on the analysis.
             Varun Singh and Jonathan Lennox asked about the differences between
             the two mechanisms, and where the variation in overheads came from:
             it's slightly different information being reported, XR vs regular
             RTCP, per-SSRC reporting overheads in RTCP vs RTP header extension
             overheads, and so on.
          
             Varun Singh asked if the group could give guidance on how to reduce
             reporting overheads. Colin Perkins suggested the congestion feedback
             draft (draft-ietf-rmcat-rtp-cc-feedback) would be a good place to do
             this, since it has related analysis already.
          
             Jonathan Lennox asked if signalling was needed for the RTCP extensions
             we propose. Colin Perkins believes it is needed, but that we have the
             mechanisms required already if the design team proposal is used.
          
             The chairs asked if there was agreement to move the design team draft
             on to AVTCORE for further development. In a hum, the consensus of the
             room was strongly to do so.
          
          
          
          ## Next steps for the RMCAT WG
          
             The chairs led a discussion of the next steps for the working group,
             now the initial candidate congestion control algorithms are complete.
          
             The group first considered interactions between applications and RTP
             flows (draft-ietf-rmcat-app-interaction-01) and between applications
             and codecs (draft-ietf-rmcat-cc-codec-interactions-02), and also the
             overall congestion control framework (draft-zhu-rmcat-framework-00).
          
             Varun Singh noted that the cc-codec-interactions draft is relatively
             mature, but the app-interaction draft has been overtaken by events
             and may no longer be useful to complete. Zahed Sarker suggested that
             the framework tried to lay the groundwork, and implicitly says what
             the app-interaction draft was going to say. Mirja Kuehlewind slightly
             disagreed, stating that the framework is for people who want to work
             on congestion control, codec-interactions is for codec people, and
             app-interaction is for applications authors - they have different
             audiences and should address different things.
          
             Varun Singh reminded that the goal was that the framework should be
             adopted by the candidates but this never happened. Mirja Kuehlewind
             agreed, but noted that this was because the group didn't want to
             delay the candidates waiting for the framework to be complete. Anna
             Brunstrom suggested that there's value in aligning with the framework
             if we move several candidates to proposed standard but perhaps not at
             the stage of experimental RFCs.
          
             The chairs asked if the group could see benefit in completing these
             drafts. Varun Singh and Zahed Sarker agreed that there was, for the
             cc-codec-interactions and the framework, but perhaps not for the
             app-interactions. Zahed noted that there's probably not a huge amount
             of work to align the framework and cc-codec-interactions. Overall,
             there seemed general agreement that we should keep these two drafts,
             mostly for when we take things to proposed standard, but there was
             less interest in app-interactions. Varun Singh and Zahed Sarker will
             review cc-codec-interactions and the framework and come back to the
             mailing list with a proposal on how to proceed with these documents.
          
             The group then discussed how to evaluate the candidate and progress
             the candidate algorithms to standards track. Varun Singh and Sergio
             Mena discussed the benefits and trade-offs of simulations, noting
             that they're useful to compare algorithms and to go from ideas to
             experimental drafts, but perhaps insufficient to go the Proposed
             Standard.
          
             Colin Perkins asked if we need formalised experiments to perform to
             judge if work is ready for Proposed, or if deployment results are
             needed.  Mirja Kuehlewind noted that we're looking to collect real
             world
             experiences with the candidates. Randell Jesup agreed that we should be
             trying the candidates in the wild, and stated that Mozilla was willing
             to help integrate candidates for testing. Varun Singh also noted that
             callstats.io was willing to help with evaluation.
          
             Anna Brunstrom noted that we still need comparison of the proposals
             since much of the evaluation is individual. She also reminded the group
             that don't have evaluations showing behaviour with the common feedback
             format, and that these will be needed before candidates can progress to
             Proposed standard.
          
             Mirja Kuehlewind noted that the bar for publishing as Experimental is
             not high but for Proposed Standard it's much higher: "we're sure this
             works well and are recommending it". The chairs concluded by suggesting
             that next steps should be to collect deployment results and experiences
             with the candidate algorithms and common feedback format, to allow
             us to
             make an informed decision on how to proceed. Proponents of the various
             candidates are encouraged to bring their evaluation results, however
             preliminary, to the group for discussion in future meetings.
          
          
          ## Other Business
          
             Varun Singh reminded the group that he presented work on a FEC-based
             congestion control algorithm to the group some years ago. They intend
             to re-submit this work soon, for consideration as an experimental RFC.
          
          
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