Re: [6tisch] Opsdir last call review of draft-ietf-6tisch-architecture-22

["Pascal Thubert (pthubert)" <[e-mail]>]

Hello Qin

I looked at it again and found that it was great to move 

     3.8.  Communication Paradigms and Interaction Models  . . . . .  21

But not such a great idea to move 

     4.2.  Network Access and Addressing . . . . . . . . . . . . . .  23
       4.2.1.  Join Process  . . . . . . . . . . . . . . . . . . . .  23
       4.2.2.  Registration  . . . . . . . . . . . . . . . . . . . .  25

So my suggestion for the latter is to better introduce the join process and the registration in section 3.1.
Proposed text:

'
6TiSCH nodes join a mesh network by attaching to nodes that are
   already members of the mesh (see Section 4.2.1).  The security
   aspects of the join process are further detailed in Section 6.  In a
   mesh network, 6TiSCH nodes are not necessarily reachable from one
   another at Layer-2 and an LLN may span over multiple links.

   This forms an homogeneous non-broadcast multi-access (NBMA) subnet,
   which is beyond the scope of IPv6 Neighbor Discovery (IPv6 ND)
   [RFC4861][RFC4862]. 6LoWPAN Neighbor Discovery (6LoWPAN ND)
   [RFC6775][RFC8505] specifies extensions to IPv6 ND that enable ND
   operations in this type of subnet.

   Once it has joined the 6TiSCH network, a node acquires IPv6 Addresses
   and register them using 6LoWPAN ND.  This guarantees that the
   addresses are unique and protects the address ownership over the
   subnet, more in Section 4.2.2.

'

Does that work?

Pascal

> -----Original Message-----
> From: Pascal Thubert (pthubert)
> Sent: jeudi 27 juin 2019 16:48
> To: Qin Wu <[e-mail]>; [e-mail]
> Cc: [e-mail]; [e-mail]; [e-mail];
> Eliot Lear (elear) <[e-mail]>; Carlos Pignataro (cpignata)
> <[e-mail]>
> Subject: RE: Opsdir last call review of draft-ietf-6tisch-architecture-22
> 
> Hello Qin
> 
> Many thanks for your review and for the important amount of time you
> obviously spent on our work. This is really appreciated.
> Please see below:
> 
> > By looking at high level architecture section, it is hard to create a
> > whole picture for what this architecture looks like and how these
> > architecture component can be put together. Also architecture
> > components defined in architecture component section seem not to align
> > with high level architecture section. For Some architecture
> > component,e.g.,Communication Paradigms and Interaction Models, Network
> > access and addressing haven't appeared in the high level architecture first.
> 
> This is an interesting comment.
> 
> If you look back at say, draft 18, the sections in the high level architecture
> have been modified and quite a bit of text went from section 3 to section 4.
> The reason is that the first reviews we got from outside the WG told us to
> shrink section 3 to the minimum, which caused us to move text to section 4.
> 
> I'm intrigued by your comment " seem not to align with high level architecture
> ". This is certainly something we need to act upon; but there is a difference
> between the fact that a discussion appears only in section 4 and a
> misalignment, which I read as a discrepancy or an inconsistency in the
> architecture. Could you please provide suggestions on where to focus without
> undoing what we did for the previous reviewers?  If this is about moving text
> back to section 3, I generally agree but need to confirm with the original
> reviewers (cc), more below.
> 
> 
> A few editorial comments and suggestions
> > 1.Section 1 IT and OT should be part of terminology section too.
> 
> Expanded both in first use and added a terminology for OT. IT is a bit too
> obvious for a terminology section isn't it?
> "
>                 <t hangText="Operational Technology:">
>                     OT refers to technology used in automation, for instance in
>                     industrial control networks. The convergence of IT and OT is
>                     the main object of the Industrial Internet of Things (IIOT).
> "
> 
> > 2.Section 2
> > ND-proxying and binding should provide reference,e.g.,RFC4389
> 
> Well, this reference would be misleading because it considers specific network
> models that are not the one we need in 6TiSCH. So we refrained from using it.
> Turns out that there is no IPv6 RFC that would be equivalent to ARP proxya
> and that we could reference. That's until now since we are doing the backbone
> router. Which is what the architecture discusses later. Sorry but I have no
> clean path to fix this...
> 
> > 3.Section 3 I
> > think Architecture Components Defined in section 4 should be
> > consistent with high level architecture, e.g.,Network access and
> > Adressing component seems not to be discussed in high level architecture
> section.
> 
> See  https://tools.ietf.org/html/draft-ietf-6tisch-architecture-17 section 3.7,
> that subsection was in section 3. This is how I thought it should be structured.
> But then it was moved to 4 on request of a previous IESG review to improve
> the clarity y making section 3 more concise.  I'm happy to move it back but cc
> the original reviewers to make sure we all agree on the final result.
> 
> Please confirm that this is effectively your recommendation.
> 
> > 4. Section 3.1 figure1
> > NME and PCE should be part of terminology section
> 
> 
> Added terminology + verified that the terms are expanded in first use.
> Note that I got the exact reverse remark from another reviewer, said
> something like expanding in first use is the IETF way and sufficient.
> A hint that there is no perfection ; )
> 
> 5.Section 4.3.1.1,1st
> > paragraph The first sentence should not belong to this section since this
> > section focuses on introduction of Hard cell.
> 
> Agreed; moved above the section boundary.
> 
> 6.Section 4.3.1.1, Section 4.3.1.2
> > Two section seesm only to discuss how to use hard cells or soft cell, but
> > doesn't define what it is. Please clarify the difference between hard cell or
> soft
> > cell
> 
> Actually it does but it could be a lot more clear.
> 
> Proposed text:
> 
> On hard cells
> 
>             "Hard" cells are cells that are
>             are owned and managed by a separate scheduling entity (e.g. a PCE)
>             that specifies the slotOffset/channelOffset of the cells to be
>             added/moved/deleted, in which case 6top can only act as instructed,
>             and may not move hard cells in the TSCH schedule on its own.
> 
> On soft cells
> 
>             In contrast, "soft" cells are cells that 6top can manage locally.
>             6top contains a monitoring process which monitors the performance of
>             cells, and can add, remove soft cells in the TSCH schedule to adapt
>             to the traffic needs, or move one when it performs poorly.
> 
> 
> > 7. Section 4.4 How this section is related to high level architecture
> > described in section 3
> 
> If that is what you have in mind, yes, this section is mostly an introduction to
> sections 4.5 to 4.8.
> If that corrects the issue as you see it, then I agree to move it to section 3.
> Please confirm that this is effectively your recommendation.
> 
> 
> > 8. Section 4.5.3 The content in section 4.5.3 is badly
> > written and hard to understand. By reading the first paragraph of section
> 4.5.3,
> > it is hard to get sense of what remote monitoring and schedule management
> > means and how reproduced figure 10 is related to remote monitoring and
> > schedule management.
> > How Remote monitoring and schedule management is different from other
> > scheduling mechanism. Please rewrite.
> 
> It is effectively a DetNet/SDN model whereby the controller assigns physical
> resources in the form of time slots.
> I can add text at the beginning of the section:
> 
> before
> "
>    The work at the 6TiSCH WG is focused on non-deterministic traffic and
>    does not provide the generic data model that would be necessary to
>    monitor and manage resources of the 6top sublayer.  It is recognized
>    that CoAP can be appropriate to interact with the 6top layer of a
>    node that is multiple hops away across a 6TiSCH mesh.
> 
>    The entity issuing the CoAP requests can be a central scheduling
>    entity (e.g. a PCE), a node multiple hops away with the authority to
>    modify the TSCH schedule (e.g. the head of a local cluster), or a
>    external device monitoring the overall state of the network (e.g.
>    NME).  It is also possible that a mapping entity on the backbone
>    transforms a non-CoAP protocol such as PCEP into the RESTful
>    interfaces that the 6TiSCH devices support.
> "
> After
> 
> "
>    Remote monitoring and Schedule Management refers to a DetNet/SDN
>    model whereby an NME and a scheduling entity, associated with a PCE,
>    reside in a central controller and interact with the 6top layer to
>    control IPv6 Links and Tracks (Section 4.6) in a 6TiSCH network.  The
>    composite centralized entity can assign physical resources (e.g.,
>    buffers and hard cells) to a particular Track so as to optimize the
>    reliability within a bounded latency for a well-specified flow.
> 
>    The work at the 6TiSCH WG focused on non-deterministic traffic and
>    did not provide the generic data model that is necessary for the PCE
>    to monitor and manage resources of the 6top sublayer.  This is
>    deferred to future work, more in Appendix A.2.2.
> 
> "
> 
> Note that since we do not do the work, it is too early to presume that  CoAP
> and PCEP will be finally adopted for this purpose and the references are
> removed.
> 
> 
> 9. Section 7 Too many thanks in the acknowledgment section, suggest to
> simplify it.
> 
> This is the only place where I really disagree. Those people helped. The WG has
> been on this spec for 5+ years. I do not see why it hurts to recognize them.
> 
> > 10.Appendix A not sure the
> > importance of this part and how these related work are related to
> architecture
> > or section 2.3.  Suggest to remove this appendix or consolidate some text
> with
> > section 2.3.
> 
> Then again your suggestion is how I would have done it and actually did in
> earlier versions. The text moved to appendix due to IESG review;  we got a
> concern that the architecture had too many references to incomplete work, so
> the text was moved. Since there were 3+ reviewers indicating the issue, I'd
> rather not undo if that's OK with you.
> 
> Please