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

Ingemar Johansson S <ingemar.s.johansson@ericsson.com> Mon, 15 November 2021 10:29 UTC

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From: Ingemar Johansson S <ingemar.s.johansson@ericsson.com>
To: "rmcat@ietf.org" <rmcat@ietf.org>
CC: "csp@csperkins.org" <csp@csperkins.org>, Ingemar Johansson S <ingemar.s.johansson@ericsson.com>
Thread-Topic: Comments on draft-ietf-rmcat-rtp-cc-feedback-07
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Date: Mon, 15 Nov 2021 10:29:47 +0000
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Archived-At: <https://mailarchive.ietf.org/arch/msg/rmcat/kWYP0P2MMHflP9zd8pFn1FFbiw0>
Subject: [rmcat] Comments on draft-ietf-rmcat-rtp-cc-feedback-07
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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

RESEARCHER

GFTL ER NAP NCM Netw Proto & E2E Perf

Labratoriegränd 11

977 53, Luleå, Sweden

Phone +46-1071 43042

SMS/MMS +46-73 078 3289

ingemar.s.johansson@ericsson.com

www.ericsson.com <http://www.ericsson.com/> 

 

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=================================