[ippm] Éric Vyncke's Discuss on draft-ietf-ippm-rfc8321bis-02: (with DISCUSS and COMMENT)

[Éric Vyncke via Datatracker <[e-mail]>]

Éric Vyncke has entered the following ballot position for
draft-ietf-ippm-rfc8321bis-02: Discuss

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DISCUSS:
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# Éric Vyncke, INT AD, comments for draft-ietf-ippm-rfc8321bis-02
CC @evyncke

Thank you for the work put into this document.

Please find below one blocking DISCUSS points (easy to address), some
non-blocking COMMENT points (but replies would be appreciated even if only for
my own education), and some nits.

Please note that Tim Winters is the Internet directorate reviewer (at my
request) and you may want to consider this int-dir review as well when Tim will
complete the review (no need to wait for it though):
https://datatracker.ietf.org/doc/draft-ietf-ippm-rfc8321bis/reviewrequest/16061/

Special thanks to Tommy Pauly for the shepherd's detailed write-up including
the WG consensus and the justification of the intended status.

I hope that this review helps to improve the document,

Regards,

-éric

## DISCUSS

As noted in https://www.ietf.org/blog/handling-iesg-ballot-positions/, a
DISCUSS ballot is a request to have a discussion on the following topics:

### Section 5

Unsure whether I understand correctly:
```
   Color switching is the reference for all the network devices, and the
   only requirement to be achieved is that all network devices have to
   recognize the right batch along the path.
```
Why do *all network devices* have to recognize the right batch? Isn't this
transparent for them?


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COMMENT:
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## COMMENTS

### Roman's DISCUSS

Just to let you know that I support Roman Danyliw's DISCUSS point.

But, I also wonder why there is a recommendation to use this method only within
controlled domains (except to falsify measurements).

### Changes of reference types between RFC 8321 and the -bis

What is the reason why some references (e.g., RFC 3393) moved from the
normative (in RFC 8321) to the informative section (in this document).

### Section 1

```
   RFC 7799 [RFC7799] defines Passive and Hybrid Methods of Measurement.
   In particular, Passive Methods of Measurement are based solely on
   observations of an undisturbed and unmodified packet stream of
   interest; Hybrid Methods are Methods of Measurement that use a
   combination of Active Methods and Passive Methods.
```

This short summary would benefit of an "active methods" definition.

### Section 3.1

In `A safe choice is to wait L/2 time units`, some experimental feedbacks or a
theoretical reasoning would be welcome. (I am not a transport expert, but a
packet delayed a lot is probably worse than a packet loss).

### Section 3.2.1.1 using the mean

Just wondering whether the authors have experimented with other statistical
metrics, e.g., the median (more 'complex' to compute of course) or taking into
account the standard deviation ?

Also, what is the impact of the arrival rate distribution on using the mean ?

### Section 3.2.2

While this section answers my previous comment, may I suggest moving the
description of "double-marking" earlier in the flow ? It now appears "out of
the blue" ;-)

Moreover, the description is rather opaque, e.g., some examples would be
welcome.

### Section 4.3 telemetry

Is there a YANG model specified (or under specification) for data collection ?

### Section 5

```
   Additionally, in practice, besides clock
   errors, packet reordering is also very common in a packet network due
   to equal-cost multipath (ECMP).
```
Unsure whether ECMP really causes a "very common packet re-ordering". Suggest
to s/very common/common/ at least ;-)

### Section 5 bound

```
   The network delay between the network devices can be represented as a
   data set and 99.7% of the samples are within 3 standard deviation of
   the average
```
Does the above assume a specific packet distribution ?

### Section 6 fragmentation

Should there be a note about:

* IPv6 routers never fragment
* use of DF bit for IPv4

## NITS

### Capitalized Passive

Unsure whether "Passive" needs to be capitalized in the text.

### Section 3.2

s/There are three alternatives, as described hereinafter./There are three
methodologies, as described hereinafter./ ? (notably because there can only be
*TWO* alternatives AFAIK)

## Notes

This review is in the ["IETF Comments" Markdown format][ICMF], You can use the
[`ietf-comments` tool][ICT] to automatically convert this review into
individual GitHub issues.

[ICMF]: https://github.com/mnot/ietf-comments/blob/main/format.md
[ICT]: https://github.com/mnot/ietf-comments