Re: [Gen-art] Genart last call review of draft-ietf-rmcat-nada-11

["Joel M. Halpern" <[e-mail]>]

Thank you.  Those changes will address my concerns very effectively.
Yours,
Joel

On 8/13/2019 11:26 AM, Xiaoqing Zhu (xiaoqzhu) wrote:
> Dear Joel,
> 
> Many thanks for your review of this draft.  Please find our responses as below, tagged [Authors].
> 
> Best,
> Xiaoqing (on behalf of all authors)
> 
> On 8/5/19, 5:17 PM, "Joel Halpern via Datatracker" <[e-mail]> wrote:
> 
>      Reviewer: Joel Halpern
>      Review result: Almost Ready
>      
>      I am the assigned Gen-ART reviewer for this draft. The General Area
>      Review Team (Gen-ART) reviews all IETF documents being processed
>      by the IESG for the IETF Chair.  Please treat these comments just
>      like any other last call comments.
>      
>      For more information, please see the FAQ at
>      
>      <https://trac.ietf.org/trac/gen/wiki/GenArtfaq>.
>      
>      Document: draft-ietf-rmcat-nada-11
>      Reviewer: Joel Halpern
>      Review Date: 2019-08-05
>      IETF LC End Date: 2019-08-12
>      IESG Telechat date: Not scheduled for a telechat
>      
>      Summary: This document is almost ready for publication as an Experimental RFC
>      
>      Major issues:
>         It is unclear reading this RFC how the observation information is to be
>         communicated from the receiver to the sender.  At first I thought it was to
>         use the RTP Receiver report.  But there is no description of how to map the
>         fields to that report.   Then section 5.3 describes requirements for a
>         reporting mechanism, but does not seem to actually define one.   Thus, I am
>         left unclear how independent interoperable implementations of this draft can
>         be created.
>      
> [Authors]  Thanks for raising this point. The feedback format is a topic covered
> by another currently pending draft (https://tools.ietf.org/html/draft-ietf-avtcore-cc-feedback-message-04),
> which indeed aims at ensuring interoperability of independent implementations of
> RMCAT congestion control solutions.  Therefore, in this draft we only specified what type
> of information is needed (e.g., receiving rate) and the unit and bit budget it is expressed
> in (e.g., in bps in 32 bits) in the feedback from the receiver.  We also pointed out in Sec. 6.4
> that an alternative way to implement this draft would be to leverage feedback messages
> that contain per-packet information (e.g., delay and loss info) and to move all the calculations
> from the receiver to the sender.
> 
> [Author] Given the above considerations, we refrained from specifying a specific feedback
> format. However, we should perhaps add a reference pointing to the cc-feedback-message draft.
> Will do that in the next revision.
> 
>      Minor issues:
>          The document has 7 front page authors.   The shepherd writeup does not
>          comment on this. The shepherd writeup seems quite sparse.  II would have
>          expected some reference to the experimental behavior described in the draft.
>      
> [Authors] Thanks for raising the concern about long list of front page authors. We got some
> additional guidance from the AD and will make some adjustments accordingly.
> 
> [Authors] As for comments on the experimental behavior: we have presented in recent IETF meetings
> on several sets of real-world evaluations of one implementation of NADA.  But, admittedly, the draft
> is lagging behind in not yet adding pointers to those results. Your suggestion is a great one and we'll add
> corresponding pointer (see links below) and related discussions in the next version.
>   
> * https://datatracker.ietf.org/meeting/103/materials/slides-103-rmcat-nada-implementation-in-mozilla-browser-00
> * https://datatracker.ietf.org/meeting/105/materials/slides-105-rmcat-nada-update-02.pdf
> 
> 
>          This comment is just to confirm that I am reading the draft correctly.  It
>          looks like when the observed delay cross the delay boundary, the reporting
>          system reports using a smaller delay than actually approved (slightly more
>          than 1/9th of observed delay when delay is 3*QTH).  I presume this is
>          intentional, and that the various analysis pointed to evaluate the risks of
>          such false reporting?
> 
> [Authors]  Yes, your understanding is correct. The main motivation for this "delay warping"
> In the presence of persistently high queuing delay *and* presence of loss is to help the flow to
> sustain a more fair rate when competing against aggressive loss-based flows.  Will follow your
> advice and add some discussions on the potential risks involved in performing this "delay warping".
>      
>          Is it intentional in section 4.3 in the pseudo-code that the rate clipping
>          (to keep the rate between RMIN and RMAX) is only applied to the gradual
>          rate change, not to the accelerated rate change?  The later code says that
>          the clipping is always applied, which is what I would expect.
>      
> [Authors]  Thanks to the catch. The clipping is always applied.  Will fix the text accordingly.
> 
>      Nits/editorial comments:
>      
>      
> [Authors]  Thanks again for your above comments. Our next round of revision (version -12) will incorporate
> changes as mentioned in our above response.
>