[alto] Tsvart early review of draft-ietf-alto-performance-metrics-03

Brian Trammell <ietf@trammell.ch> Mon, 09 April 2018 16:35 UTC

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From: Brian Trammell <ietf@trammell.ch>
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Date: Mon, 09 Apr 2018 09:35:30 -0700
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Subject: [alto] Tsvart early review of draft-ietf-alto-performance-metrics-03
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Reviewer: Brian Trammell
Review result: On the Right Track

I've performed a (late, apologies) early TSV-ART review of
draft-ietf-alto-performance-metrics-03.

The set of metrics chosen by the document seem broadly useful and sane, and the
integration into ALTO makes sense. However, there are a few issues with the
details.

Periodic One Way Delay, RTT, and PDV are defined in terms of section 8, section
4, and section 5, respectively, of draft-ietf-ippm-initial-registry, which
specify active measurement test methodologies at layer 4 for one-way and
round-trip delay using UDP packets. This does not seem it can be measured
directly using the routing  technologies the authors have identified as their
source of information. Is the intention that dedicated active measurement
hardware be used to measure delay using UDP packets, or should these metrics
reference [RFC2679] and [RFC2681] and leave the methodology undefined, instead?

The examples for these don't make much sense: the units are expressed in
seconds, but Internet-scale delays are generally millisecond-scale, and the
examples given contain only integers. Similarly, packet loss rate is given in
percentile, but there are wide variations in usability between a path with 0%,
1%, and 2% packet loss. Is this simply an issue with the examples?

The hop count metric is underspecified: are these IP-experienced hops at layer
3, as can be measured by traceroute?

Nit: section 2.1 refers to [OSPF-TE], [ISIS-TE], [BGP-LS] and [BGP-PM], but
these are not listed as such as references in the references section. Please
use consistent reference labels.

Thanks, cheers,

Brian