Subject: [ippm] comments on draft=mathis-ippm-model-based-metrics-00

From: "Al Morton" <[email-masked]>
Date: Sun, 04 Nov 2012 10:56:01 -0500

Hi Matt,

I finally made time to read one of your new memos on the way down.

I found this new approach for model-based metrics really interesting
and encouraging, and it caused me to think of several ideas on related
work, so thanks for putting the memo together.  I support adoption of this
memo in the WG, and we can talk about ways I might be able to help.

Comments and questions:

Several times you mention progressive loss, I think you mean
some form of early discard before drastic tail drop, but not sure.
Is this a mandatory property of the measured path?

In section 3.3:

target_pipe_size = target_rate * target_RTT / target_MTU

is a unit-less quantity.  octets/sec * sec/octets

I think I know what you're getting at here, but seems odd.

Last, I havent seen any other readers look at this yet, possibly a
consequence of the 00 deadline and revised draft deadline overloads,
but I encourage others to take a look before IPPM meets.

regards,
Al
(hoping my usa.net account is subscribed...)

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From: Matt Mathis <[email-masked]>
Date: Mon, 5 Nov 2012 07:00:32 -0800

Inline
> Is this a mandatory property of the measured path?

It should be (will be).  The dots haven't been connected yet.  The
problem was described in RFC 2309, the most egregious symptoms
described in Jim Getty's talks an buffer bloat, and a much better
solution published here http://queue.acm.org/detail.cfm?id=2209336.

Modern applications function rather poorly on droptail.  Part of the
reason that the "derating" language in in the document is to provide a
phase in strategy when approximately 0% of the gear will be fully
compliant on day 1.

> I think I know what you're getting at here, but seems odd.

If you make MTU "bytes per packet" then target_pipe_size has units packets.

> but I encourage others to take a look before IPPM meets.

Thanks!  I'll see you in IPPM if not sooner.
--MM--
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