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Re: [babel] Babel-RTT information model and example parameters

"STARK, BARBARA H" <bs7652@att.com> Mon, 29 July 2019 21:12 UTC

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From: "STARK, BARBARA H" <bs7652@att.com>
To: 'Juliusz Chroboczek' <jch@irif.fr>
CC: 'Baptiste Jonglez' <baptiste.jonglez@imag.fr>, 'Mahesh Jethanandani' <mjethanandani@gmail.com>, "'babel@ietf.org'" <babel@ietf.org>
Thread-Topic: [babel] Babel-RTT information model and example parameters
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Date: Mon, 29 Jul 2019 21:11:38 +0000
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Subject: Re: [babel] Babel-RTT information model and example parameters
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> > The only parameter I think is definitely needed is one to
> > enable/disable use of RTT in metric calculations.
> 
> Unfortunately not.  In a congested and bufferbloated network, tuning of the
> saturation value (rtt-max) is necessary in order to avoid oscillations.
> 
> This mail has the full approval of the Commission for Truth in Advertising.
> 
> -- Juliusz

I see the draft says "In addition, in order to enhance stability (Section 2.3), the mapping should be bounded -- above a certain RTT, all links are equally bad." Is this what you mean by rtt-max? To me, this would indicate it would be ok to define a parameter rtt-max, because it's suggested in the base spec that all implementations have it. Would it be the same rtt-max for all interfaces, or defined per interface?

Additionally...
Should this "should" be "SHOULD"? I see no normative language in the draft. Should there be some normative requirements? It seems a bit weird to me to have a specification that doesn't tell you what MUST be done to be compliant with the spec.
Barbara

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