Subject: [Gen-art] Gen-ART review of draft-ietf-pmol-sip-perf-metrics-03.txt

From: Suresh Krishnan <[email-masked]>
Date: Wed, 19 Aug 2009 17:59:34 -0400

I am the assigned Gen-ART reviewer for
draft-ietf-pmol-sip-perf-metrics-03.txt

For background on Gen-ART, please see the FAQ at
<http://www.alvestrand.no/ietf/gen/art/gen-art-FAQ.html>.

Please resolve these comments along with any other Last Call comments
you may receive.

Summary: This draft has a few issues that need to be fixed before 
publication as a Proposed Standard.

Substantial
===========

* Section 3 Page 7

"Clock correction SHOULD be suspended during a T1 to T4 measurement 
interval, unless the time interval accuracy requirement above will be met."

I think it is inappropriate for this document to specify normative 
requirements on other protocols (e.g. NTP). e.g. Something like

"A T1 to T4 measurement SHOULD NOT be performed during clock correction, 
unless the time interval accuracy requirement above will be met."

* Section 4.1 RRD

The text describing the RRD measurement in the following figure is 
ambiguous. Why is the RRD measured from the first REGISTER and not from 
the second one?

                   UA1                 Registrar
                    |                      |
                    |REGISTER              |
             T1---->|--------------------->|
                /\  |                   401|
                ||  |<---------------------|
               RRD  |REGISTER              |
                ||  |--------------------->|
                \/  |                   200|
             T4---->|<---------------------|
                    |                      |

The text reads "...first bit of the initial REGISTER message
*containing the necessary information* (emphasis mine)..." which 
pertains more to the second REGISTER than the first.

* Section 4.6. Hops per Request

It is not clear how or where this measurement is performed. The way I 
see it, this measurement requires co-ordination between the two 
endpoints and this makes it very different from the other metrics in 
this document. I think this needs to be highlighted and/or clarified.

Minor
=====

* Section 4.12.2. Failed Session Completion

This does not seem to be used anywhere. Is there a missing metric or is 
this section redundant? Also this does not seem to be the complement of 
the Successful Session Completion metric.

Thanks
Suresh