Last Call Review of draft-ietf-6tisch-architecture-20
review-ietf-6tisch-architecture-20-tsvart-lc-fairhurst-2019-06-20-00

TSV-ART Reviewer: Gorry Fairhurst
Review result: Ready with Issues

This document has been reviewed as part of the transport area review team's
ongoing effort to review key IETF documents. These comments were written
primarily for the transport area directors, but are copied to the document's
authors and WG to allow them to address any issues raised and also to 
the IETF
discussion list for information.

When done at the time of IETF Last Call, the authors should consider this
review as part of the last-call comments they receive. Please always CC
tsv-art@ietf.org if you reply to or forward this review.

The document primarily describes an architecture that provides a link 
layer /subnet method to support IPv6 datagrams over the TSCH mode of 
IEEE 802.15.4.

Intended status
-------------

The document is proposed with standards track status, but appears to 
mainly provide informational background about the architecture. There 
are no normative requirements made. This could be published as 
informational.

* Use of References:

I suggest someone checks the presence of a large body of informative 
references to current working group documents - rather than normative 
citation of the published work.
I am concerned about citing individual work in progress within the body 
of the document:

Final para of Section 3.1 makes a reference to an individual draft that 
appears to target the ROLL WG.

Section 3.2 makes reference to an individual draft to describe multicast 
[ID.thubert…]
Section 4.1.1 makes a reference to an individual draft that appears to 
target the ROLL WG,
mentioned twice as defining something,
Section 4.1.1 makes a reference to an individual draft that appears to 
target the ROLL WG.

* References to unchartered individual work in Appendix.

Appendix A describes a set of architectural dependencies that depend on 
non-adopted (individual) documents or work not formally chartered by the 
IETF. This description raises concerns about what happens when the 
present document is published, and this work is not taken-up or some 
alternative proposal is instead pursued, it would be safer to remove 
these references - or at least to confine them to an appendix that 
clearly sets out that this work is individual work in progress.


Transport issues
--------------

* "Transport Mode"

Section 4.7.1 describes a "transport mode”, but from the perspective of 
the IETF transport area is not a transport. While there have been many 
interpretations of “transports” by SDOs and IETF Specs, I suggest it 
would beneficial to add a few words refining the meaning of the words in 
the present usage: e.g. that this does not provide a “transport 
protocol”, but provides a way to send and receive IPv6 packets that 
carry a transport protocol.

* The IPv6 Flow Label may be zero

Section 4.7.1.1 seems to imply that IPv6 packets carry a non-zero flow 
label value. Whilst I would support that desire, there are still cases 
where no flow label is set, and this casts should be described (or 
noted) in the text.

* Assumption about IPv6 MTU

Section 4.7.3 notes the IPv6 MTU is 1280 B. This is not true, please 
rewrite this sentence. It could be that the intentional was to state the 
minimum IPv6 MTU or something else was intended?

* Possible PHB - reference to not chartered transport work.

Section 4.8.3 describes a transport feature (diffserv PHB) and appears 
to promote an individual draft. The particular drafts appear to target 
tsvwg, but I do not recall these being proposed to that WG for adoption, 
and therefore this seems a little presumptuous to appear in the main 
body of text or within the architecture. The reference is also out-of-date.
- I suggest it would be sufficient to explain that a future document 
could define a PHB for this purpose and refer to the IANA registry as 
the place where IETF-defined PHBs are listed.
- Please this without citing a ref to an individual spec.?
- In addition, I think if this sections retained, it needs to be moved 
to the appendix.


Editorial Issues
-------------

The following editorial issues should be addressed:

The document makes frequent use of the phrase “in order to”, which in 
most (all?) cases could be replaced more simply by “to” without loss of 
meaning. This would remove several cases where the sentence could 
currently be mis-interpreted as requiring temporal ordering of the actions.

Section 4.3.3: “infoirmation” should be “information”.

Section 1, Sentence “Distributed is a concurrent model that..”. i could 
not understand the intended meaning of this sentence.

“such a Advance metering”. “a” maybe should be “as”? Why is Advanced 
capitalised, I think this sentence lacks some necessary explanation, 
please add, and provide a reference.

CoJP - no reference is provided to where this is specified.