[Gen-art] Genart last call review of draft-ietf-rmcat-eval-test-08

Stewart Bryant <stewart.bryant@gmail.com> Mon, 04 February 2019 19:28 UTC

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From: Stewart Bryant <stewart.bryant@gmail.com>
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Subject: [Gen-art] Genart last call review of draft-ietf-rmcat-eval-test-08
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Reviewer: Stewart Bryant
Review result: Almost Ready

I am the assigned Gen-ART reviewer for this draft. The General Area
Review Team (Gen-ART) reviews all IETF documents being processed
by the IESG for the IETF Chair.  Please treat these comments just
like any other last call comments.

For more information, please see the FAQ at


Document: draft-ietf-rmcat-eval-test-08
Reviewer: Stewart Bryant
Review Date: 2019-02-04
IETF LC End Date: 2019-02-11
IESG Telechat date: Not scheduled for a telechat


A well written documents an close to being ready for publication.

I am concerned that the Security section is weak on use outside a
controlled environment.

There are a fair number of minor issues and nits that need attention,
but most of them are simple to fix.

One concern that I have that I doubt is readily fixable is that long
multi-nested lists do not work well in paginated ASCII with line spaces
and sometimes it is difficult to be sure of the context of a test element note.

Major issues:

8.  Security Considerations

   The security considerations in [I-D.ietf-rmcat-eval-criteria] and the
   relevant congestion control algorithms apply.  The principles for
   congestion control are described in [RFC2914], and in particular any
   new method MUST implement safeguards to avoid congestion collapse of
   the Internet.

   The evaluation of the test cases are intended to be run in a
   controlled lab environment.

SB> I wonder if there shouldn't me a MUST in that sentence?
SB> There have been issues on SP networks with users running unsuitable
SB> performance benchmarks on live networks, including complaints to the
SB> operators concerning the results achieved.

   Hence, the applications, simulators and
   network nodes ought to be well-behaved and should not impact the
   desired results.  It is important to take appropriate caution to
   avoid leaking non-responsive traffic from unproven congestion
   avoidance techniques onto the open Internet.

SB> Again I am surprised this is not much stronger in prohibiting
SB> use on the Internet.


Minor issues:

   This memo describes a set of test cases for evaluating congestion
   control algorithm proposals for real-time interactive media.

SB> It would be useful to add here the statement in the abstract that
SB> these tests should be done in a controlled environment.


   Expected behavior: depending on the convergence observed in test case
   5.1 and 5.2, the candidate algorithm may be able to avoid congestion
   collapse.  In the worst case, the media stream will fall to the
   minimum media bit rate.

SB> Do you need to specify the variant of TCP? You do state it later, but some
comment here would be useful. SB> What behaviour do you expect the TCP to show.
It would be bad if SB> an aggressive media application kill the TCP completely.

   the first flow
   (S1) MUST arrive at a steady-state rate approximately twice of that
   of the other two flows (S2 and S3).

SB> I am not sure what you mean by priority I assume that you mean
SB> QoS ranking in the routing system. In which case I don't see
SB> how you can expect the result you specify.


   Expected behavior: the candidate algorithm is expected to achieve
   full utilization at both bottleneck links without starving any of the
   three congestion controlled media flows.

SB> I am not sure what you mean by this. Do you mean that the bottlenecks
SB> will saturate, but make no comment about how much of the bottleneck
SB> capacity each flow gets for itself?


Nits/editorial comments:

 Checking nits according to https://www.ietf.org/id-info/checklist :

  ** There are 9 instances of too long lines in the document, the longest one
     being 4 characters in excess of 72.

  == Outdated reference: A later version (-06) exists of


3.  Structure of Test cases

SB> In the text below it was sometimes hard to get the context right in the
SB> triple (or more) nested list. Please consider using subsections or some
other SB> demarcation.


         +  Bottleneck queue type: for example, Droptail, FQ-CoDel, or

SB> There need references, and by convention expansion on first use.


         +  Path loss ratio: characterizes the non-congested, additive,
            losses to be generated on the end-to-end path.  MUST
SB> s/MUST/This MUST/ ?


       B.  Variation in sending bit rate and goodput.  Mainly observing
           the frequency and magnitude of oscillations.

SB> goodput needs a reference or a definition. I don't think it is a
universally known term.


   Expected behavior: the candidate algorithm is expected to detect the
   path capacity constraint, converges to the bottleneck link's capacity
SB> s/converges/converge/


Due to asymmetric nature of the link

SB> s/Due to/Due to the/


SB> Is there a diagram error in the figure above?

     Figure 6: Testbed Topology for TCP vs congestion controlled media


   have the same bandwidth share on the link.  It has to make it's way


The candidate algorithm MUST reflect the relative priorities
   assigned to each media flow.  In the previous example,
SB> An explicit reference to the test would help the reader