Subject: [ippm] I-D ACTION:draft-ietf-ippm-owmetric-as-00.txt

From: [email-masked]
Date: Mon, 01 Jul 2002 06:35:04 -0400

A New Internet-Draft is available from the on-line Internet-Drafts directories.
This draft is a work item of the IP Performance Metrics Working Group of the IETF.

	Title		: One-Way Metric Applicability Statement
	Author(s)	: H. Uijterwaal, M. Kaeo
	Filename	: draft-ietf-ippm-owmetric-as-00.txt
	Pages		: 7
	Date		: 28-Jun-02
	
Active traffic measurements are starting to become more widely used to
ascertain network performance characteristics.  All active measurement
systems have the capability to measure one-way delay and one-way loss
metrics, as defined in RFC2679 [1] A One- way Delay Metric for IPPM and
RFC 2680 [2] A One-way Packet Loss Metric for IPPM, respectively.  To
ensure that the resulting numbers have some meaning, we attempt to
characterize how the measurements are taken and what would ensure that
the end numbers are indeed meaningful.  This document describes an
applicability statement (formerly known as best current practices) for
measuring the one-way delay and one-way loss metrics in operational
networks.

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From: stanislav shalunov <[email-masked]>
Date: 03 Jul 2002 12:35:04 -0400

I have a few nit-picks about the document:

Section 3.4 `Test duration' makes an assertion about desirability of
continuous monitoring that on the surface is obvious but in fact
involves a subtle trade-off with ability to differentiate between
losses and measurement device failures when periods of extended losses
are involved.

Section 3.5 `Data volumes' appears to fail to explain why the
measurement traffic needs to be low volume.  In fact, for some
measurements it needs to be low and for some it must be comparable
with link capacity.  It should be made clear that specific metrics
(such as one-way loss and delay) and specific methodology is
discussed.  Further, the number 3% is pulled out of the hat: 300Mb/s
of active delay and loss measurement traffic on a 10Gb/s network is
surely excessive, isn't it?

Section 5.0 `Reporting the IPDV metric' says that `the distribution
generally is not Gaussian and the sigma is not well defined'.  Many
non-Gaussian distributions happen to have finite standard deviation.
Reporting standard deviation makes sense for more than Gaussian
distribution, too.

-- 
Stanislav Shalunov		http://www.internet2.edu/~shalunov/

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From: "Henk Uijterwaal (RIPE-NCC)" <[email-masked]>
Date: Thu, 4 Jul 2002 10:40:31 +0200 (CEST)

Hi Stas,

> losses and measurement device failures when periods of extended losses

I'm not quite sure if I understand this comment.

> with link capacity.

Such as?

> It should be made clear that specific metrics (such as one-way loss and
> delay) and specific methodology is discussed. Further, the number 3% is
> pulled out of the hat: 300Mb/s of active delay and loss measurement
> traffic on a 10Gb/s network is surely excessive, isn't it?

Yes and no. The 3% number comes from discussions with providers, who
typically claim that "using a few percent" of the total capacity to
monitor the performance of their equipment.  If you have a better number,
then I'd like to hear it. Also see section 3.1, if we send 3% of 10 Gb/s
measurement traffic, will we see all interesting variations in traffic?

> Reporting standard deviation makes sense for more than Gaussian

Yes.  However, look in our latest PAM paper (or wait until my Yokohama
presentation) to see some of the typical IPDV distributions.  Reporting
sigma for these distributions simply doesn't make sense.

Henk

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