Re: [rmcat] Comments on draft-ietf-rmcat-rtp-cc-feedback-07

[Anna Brunström <[e-mail]>]

Hi Ingemar,

Thanks for the comments on the draft!

Colin: please consider them as part of the input from the WGLC that was just announced.

BR,
Anna

From: rmcat <[e-mail]> On Behalf Of Ingemar Johansson S
Sent: den 15 november 2021 11:30
To: [e-mail]
Cc: Ingemar Johansson S <[e-mail]>; [e-mail]
Subject: [rmcat] Comments on draft-ietf-rmcat-rtp-cc-feedback-07

Hi

I promised to review draft-ietf-rmcat-rtp-cc-feedback-07
Overall a very well written draft, just a few comments of minor nature, not sure if they are useful but anyway..


Page 3, 3rd para : Unlike "unpaced" TCP, multimedia traffic is naturally paced to the frame rate of the media encoder (for instance 50 frames/second), so issues with coalescing that can occur with TCP and very sparse ACKs, does not occur with multimedia traffic. What instead puts a limit is how fast the algorithm should react to congestion and how it is designed.

Section 3.1 para 3 : Non-compound is mentioned but RFC5506 is referenced later

Section 3.1 equations : I checked the equations and they seem to match. But when I tried to verify the values in the tables I get different values, a simple hack in matlab/octave gives
Table 1
>> n=2;Tf=0.02;Nr=[2,4,8,16];Sc=142;Snc=62;Nnc=0;Brtcp=8*(n*(Sc+Nnc*Snc))./(Nr*Tf*(1+Nnc))/1000
Brtcp =
   56.8000   28.4000   14.2000    7.1000
>> n=2;Tf=0.06;Nr=[2,4,8,16];Sc=142;Snc=62;Nnc=0;Brtcp=8*(n*(Sc+Nnc*Snc))./(Nr*Tf*(1+Nnc))/1000
Brtcp =
   18.9333    9.4667    4.7333    2.3667

Table 2
>> n=2;tf=0.02;Nr=[2,4,8,16];Sc=142;Snc=62;Nnc=1;Brtcp=8*(n*(Sc+Nnc*Snc))./(Nr*tf*(1+Nnc))/1000
Brtcp =
   40.8000   20.4000   10.2000    5.1000
>> n=2;tf=0.06;Nr=[2,4,8,16];Sc=142;Snc=62;Nnc=1;Brtcp=8*(n*(Sc+Nnc*Snc))./(Nr*tf*(1+Nnc))/1000
Brtcp =
   13.6000    6.8000    3.4000    1.7000

Section 3.2 : Here it obviously gets more tricky. What would perhaps have been more helpful is to present the equation for Brtcp here as well.

Section 5: See this more as a question, is a security considerations section needed as this memo does not propose any new feedback format ?

/Ingemar
================================
Ingemar Johansson  M.Sc.
Master Researcher

Ericsson Research
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GFTL ER NAP NCM Netw Proto & E2E Perf
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