Re: [bmwg] Eric Rescorla's No Objection on draft-ietf-bmwg-sdn-controller-benchmark-meth-08: (with COMMENT)

bhuvaneswaran.vengainathan@veryxtech.com Wed, 18 April 2018 08:27 UTC

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Subject: Re: [bmwg] Eric Rescorla's No Objection on draft-ietf-bmwg-sdn-controller-benchmark-meth-08: (with COMMENT)
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Hi Eric,
Thank you for your feedback on this draft. Please find below my response inline with tag [Bhuvan] 

@Al, Thanks for taking care of Eric's last feedback.
Best regards,
Bhuvan

On Wed, Apr 18, 2018 at 02:44 AM, Eric Rescorla  wrote:
Eric Rescorla has entered the following ballot position for
draft-ietf-bmwg-sdn-controller-benchmark-meth-08: No Objection

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----------------------------------------------------------------------
COMMENT:
----------------------------------------------------------------------

Rich version of this review at:
https://mozphab-ietf.devsvcdev.mozaws.net/D3948 (https://mozphab-ietf.devsvcdev.mozaws.net/D3948)

COMMENTS
reported.

4.7. Test Repeatability

To increase the confidence in measured result, it is recommended
that each test SHOULD be repeated a minimum of 10 times.

Nit: you might be happier with "RECOMMENDED that each test be repeated
...."

Also, where does 10 come from? Generally, the number of trials you
need depends on the variance of each trial.
[Bhuvan] The RECOMMENDED number 10 was arrived based on our experience during the benchmarking. I will discuss with other authors for changing SHOULD to RECOMMENDED. 
Test Reporting

Each test has a reporting format that contains some global and
identical reporting components, and some individual components that
are specific to individual tests. The following test configuration
parameters and controller settings parameters MUST be reflected in

This is an odd MUST, as it's not required for interop.[Bhuvan] The intent of specifying MUST is to capture relevant test parameters to enable Apple to Apple comparison of test test results across two testers/test runs. 
5. Stop the trial when the discovered topology information matches
the deployed network topology, or when the discovered topology
information return the same details for 3 consecutive queries.
6. Record the time last discovery message (Tmn) sent to controller
from the forwarding plane test emulator interface (I1) when the
trial completed successfully. (e.g., the topology matches).

How large is the TD usually? How much does 3 seconds compare to that?
[Bhuvan] The test duration varies depends on the size of the test topology. For a smaller topology (3 - 10) the TD was within a minute. So we kept the query interval of 3 seconds to accomodate smaller and larger topologies.
Total Trials

SUM[SQUAREOF(Tri-TDm)]
Topology Discovery Time Variance (TDv)  ----------------------
Total Trials -1

You probably don't need to specify individual formulas for mean and
variance. However, you probably do want to explain why you are using
the n-1 sample variance formula. 

[Bhuvan] We have added both formulas based on the feedback received in the mailing list.  We are using n-1, as it is commonly used variance measure. Do we need an explanation here or providing any reference to this is sufficient?
Measurement:

(R1-T1) + (R2-T2)..(Rn-Tn)
Asynchronous Message Processing Time Tr1 = -----------------------
Nrx

Incidentally, this formula is the same as sum_i{R_i} - sum_i{T_i} 

[Bhuvan]  Good suggestion, we will incorporate in the next revision. 

messages transmitted to the controller.

If this test is repeated with varying number of nodes with same
topology, the results SHOULD be reported in the form of a graph. The
X coordinate SHOULD be the Number of nodes (N), the Y coordinate
SHOULD be the average Asynchronous Message Processing Time.

This is an odd metric because an implementation which handled overload
by dropping every other message would look better than one which
handled overload by queuing. 

[Bhuvan] Believe Al has clarified this feedback. As suggested by Al, we will update the BCP language in the reporting section.
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