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RTP Media Congestion Avoidance Techniques (Active WG)
Tsv Area: Mirja K├╝hlewind, Spencer Dawkins | 2012-Sep-25 —  

IETF-100 rmcat minutes

Session 2017-11-15 1330-1500: Orchard - Audio stream - rmcat chatroom


minutes-100-rmcat-00 minutes

          RTP Media Congestion Control Working Group Minutes - IETF 100
          Reported by Colin Perkins and Gorry Fairhurst
          The RMCAT working group met at IETF 100 in Singapore, on 15 November 2017.
          The chairs started the meeting with a review of the working group status:
          - The cc-requirements, coupled-cc, and SCReAM drafts are with the
          RFC Editor
          - The SBD draft has passed WG last call and the write-up is ready, minor
            issues to resolve then will go to the IESG
          - The NADA draft has been updated based on WG last call comments, and is
            on the agenda for this meeting
          - The GCC draft is waiting an update from the authors
          - The eval-test draft is blocked on eval-criteria, and eval-criteria is
            waiting on an update. Varun Singh volunteered to do this update at the
            last meeting, and it's hoped this will be received soon. If not, the
            chairs will try to find an additional editor to complete the work.
          - The wireless tests draft has no open issues. Reviews and implementation
            experience are needed.
          - The video-traffic-model draft is ready for review, and close to WG last
          - The feedback-message draft will be discussed later in the meeting.
          - The cc-feedback draft has expired, but will be updated to track changes
            to the feedback-message.
          - The cc-codec-interactions and framework draft are blocked waiting for a
            proposal for updates that Varun and Zahed volunteered at IETF 99. Zahed
            noted that the framework needs only small updates to align with the RTP
            topologies RFC, but that it's unclear how to align cc-codec-interactions
            and the framework, and he's had no time to review. Thinks the framework
            is in good shape. Xiaoqing Zhu noted that Cisco is open sourcing code
            that implements the framework, but again she has issues finding time.
            Zahed suggested to ship the framework, and leave cc-codec-interactions
            until later: he's not convinced they need to align. Zahed to discuss
            Varun soon, and update the WG on the mailing list with how they plan to
          The status update concluded with a review of the milestones.
          ## NADA
          Xiaoqing Zhu summarised the changes made to the NADA draft based on
          implementation feedback from Julius Flohr, and presented performance
          results to show their benefits and the behaviour of the algorithm.
          She also noted that they'd added Fixed-FPS and Trace-driven codecs
          to their
          synthetic codecs test suite. These are believed to be more realistic than
          the previously implemented models, and have been used for their latest
          experiments. Xiaoqing believes the video-traffic-model draft has now been
          completed, but it needs further review from the working group.
          Xiaoqing noted that their ns3-rmcat RMCAT simulation code, that has been
          previously discussed in the working group, has now been made open source.
          Jonathan Lennox asked if their simulator uses RTCP feedback as in the
          cc-feedback draft? Not yet, since the cc-feedback draft is still changing.
          An update will be submitted to address review comments from Roland Bless
          and Michael Welzl, then they believe the draft will be completed. It's
          expected this will be ready for a second WG last call.
          Ingemar Johansson asked if the evaluations were with CBR-like video, or
          something more realistic. They're a mixture.
          Xiaoqing noted their next steps are to experiment with embedding NADA in
          Mozilla browsers. Jonathan Lennox asked what feedback mechanism they're
          using, and if they could use the cc-feedback draft.
          ## SCReAM
          Ingemar Johansson presented experiments using SCReAM for congestion
          of video over mobile 4G/5G links for remote control of vehicles. This
          low latency and good quality video, so similar requirements to interactive
          video applications that RMCAT has targetted.
          Their implementation uses a non-standard RTCP feedback format, but they
          intend that this will be replaced with the cc-feedback message once it's
          Ingemar noted that video codecs can be challenging to work with, and have
          limited tuning capabilities in many cases. Randell Jesup asked a number of
          questions for clarification on these results.
          The perform strea prioritisation using weighted credit based scheduling.
          Ingemar noted some issues with this priorisation, and it works quite ok,
          but there is room for improvement. He believes use of ECN would improve
          performance (the ECN results presented used a simulated bottleneck, but
          the others use a real network).
          Xiaoqing Zhu asked for clarification on the packet loss rates observed,
          and whether there were self-induced losses as the flows compete. Ingemar
          noted that it was around 0.5% packet loss in the real network tests. It
          would perhaps be interesting to see packet loss traces, and to explore
          the effects of non-congestive packet loss on the algorithms. There was
          some discussion about packet loss patterns, and it seems that it was a
          little bursty.  There was also discussion on the causes of loss in the
          LTE scenario.
          ## RTCP Feedback for Congestion Control
          Zahed Sarker presented the results of the design team on RTCP feedback.
          The design team was formed after IETF 94 to propose a generic congestion
          feedback RTCP message. This has now been done, and the draft has been
          passed to the AVTCORE working group to finalise. Expected outcome is a
          standards track RFC from AVTCORE. The chairs thanked the design team for
          their work.
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