Subject: [tcpm] rto-consider: "regularly" taking RTT samples

From: "Mark Allman" <[email-masked]>
Date: Fri, 22 Nov 2019 08:45:34 -0500

Hi Gorry!

Thanks for all the comments.  I am going to work through them and
hack on the document.  I am addressing a couple of the easier
comments today.  But, will address them all soon.

I-D>> In steady state the RTO SHOULD be set based on recent
I-D>> observations of both the FT and the variance of the FT.

Gorry> - I don’t think these are wrong, but I think the advice is
Gorry>   not very crisp for a BCP - how recent? How does this relate
Gorry>   to Comment 3?

The "recent" here is defined in requirement (2b), as you note.  So,
it isn't meant to be crisp here.  I can see two paths:

(1) Remove the word "recent" from here.  The overall point of
    guideline (2a) is really that the RTO SHOULD be based on
    observations---i.e., not statically set.  The notion of "recent"
    isn't hugely important here as it is concretely developed in
    (2b).

OR,

(2) We could leave the "recent" in (2a) with a forward reference to
    indicate we are not leaving this as nebulous somehow.  E.g.,
    "... recent observations---as defined below---of both ..." if
    folks think keeping this notion (colloquially) in (2a) is a good
    idea.

I am pretty indifferent to both options.

I-D>> FT observations SHOULD be taken regularly ...
I-D>>
I-D>> The notion of "regularly" SHOULD be defined as at least once
I-D>> per RTT or as frequently as data is exchanged in cases where
I-D>> that happens less frequently than once per RTT.

Gorry> - To me, reads as impossible RFC2119 text, is this a
Gorry>   definition or something else? or Designs are REQUIRED to
Gorry>   define ... etc.

I really can't parse the complaint here (which is probably because
you well explained it, but since I wasn't there the slide isn't
conveying that to me).  I don't see this impossibility you are
suggesting.

That said,

Gorry> I hope this actually is intended to be:
Gorry> FT observations SHOULD be taken be at least once
Gorry> per RTT or as frequently as data is exchanged in cases where
Gorry> that happens less frequently than once per RTT.

This is in fact the intent and I am happy to use those words.

allman

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From: G Fairhurst <[email-masked]>
Date: Sat, 23 Nov 2019 09:31:14 +0800

Hi Mark!

> I am pretty indifferent to both options.
Omitting the word (a) is indeed easy. I suspect the new formulation of 
(b) effectively defines regularly, so a recent sample should be available.
> conveying that to me).  I don't see this impossibility you are
Sorry, happy to explain why I thiunk this can be misread, but reading-on 
we already have a solution that works for me.
> This is in fact the intent and I am happy to use those words.
Then let's do that.
> allman
Gorry

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From: "Mark Allman" <[email-masked]>
Date: Sun, 24 Nov 2019 09:53:46 -0500

> Omitting the word (a) is indeed easy. I suspect the new
> formulation of (b) effectively defines regularly, so a recent
> sample should be available.

I removed the word from my version.

>> This is in fact the intent and I am happy to use those words.

I tweaked the words ever-so-slightly to be even more specific:

        (b) FT observations SHOULD be taken and incorporated into the
            RTO at least once per RTT or as frequently as data is
            exchanged in cases where that happens less frequently than
            once per RTT.

The supporting (non-normative) text that followed is still there.

Seem OK?

allman

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From: "Gorry (erg)" <[email-masked]>
Date: Mon, 25 Nov 2019 09:02:24 +0000

Yes works for me.

Gorry

> On 24 Nov 2019, at 14:53, Mark Allman <[email-masked]> wrote:
> 
>