Re: [6tisch] removing the 'e'

[Pat Kinney <[e-mail]>]

Thanks Kris;

Let's review your points:

- IE IDs:  When 15.4e was introduced, we allowed vendors to freely use 25 non-standardized IDs with the explicit warning that another vendor could be using that ID creating a conflict, destroying coexistence. Since that time we have seen a significant number of requests for IE IDs, so given the limited number of IDs and the fact that there really is no vendor coexistence with the original scheme, we changed to one specific vendor ID where the vendor's OUI is required to make the IE unique.

- macTsRxOffset: the basic intent of macTsRxOffset is to center the transmission start within the range of 2200 µs (macTSRxWait). So the transmitter's macTsTxOffset (2120µs) should be 1100µs (macTsRxWait/2) greater than macTxRxOffset(1020µs).  However, 15.4e mistakenly used the term "frame" when it actually meant "PPDU". The start of the frame occurs 192 µs after the start of the PPDU or packet. 15.4e's value of 1120µs was an extra 100µs to compensate for the PHY components (which are really 192 µs). In summary, we could either continue to use the term frame with macTxRxOffset=1020µs, or use PPDU and add 192 µs.

- use of short addresses in nonce generation: 15.4e changed the nonce requirement of 15.4-2011, from requiring the use of the 8-octet extended address to allowing the usage of the short address (btw - all operations modes not just TSCH). It is generally understood that using the short address in the nonce generation is very problematic. Even if the short address is unique inside the PAN, there could be multiple PANs sharing the same keying material and using same short address for multiple devices. Using only the short address and not a combination of PANId and macShortAddress since it also puts another requirement, that short address needs to be unique over all PANs which use same key, not only unique inside the current PAN.

- TLV vs. LTV: The revision retains the IE formatting from 15.4e, it remains backward compatible.  The statement "the fact that such a change, with little to no practical value, would require continuous debate over many meetings is a sign that backward compatibility is not top of mind for a good part of the WG" is totally incorrect.  All standards organizations require that all individuals and organizations be heard, and they were in a thoughtful manner.

In summary, the changes done in the revision were to correct issues and problems.  The standardized TSCH IE IDs were not changed, rather a method was added to eliminate vendor conflicts in non-standardized IDs and the extra IDs were put back into reserve.  The macTxRxOffset was changed to be consistent with the correct terminology. While using the short address for nonce generation is not compliant to the revision, the group consensus was that it's not appropriate to knowingly degrade security, hence reverting back to the 802.15.4-2011 method.

Pat Kinney
Kinney Consulting LLC
IEEE 802.15 WG vice chair, TG chair
ISA100.11a WG chair
O: +1.847.960.3715
[e-mail]

On 30, Mar2015, at 21:59, Kris Pister <[e-mail]> wrote:

Pat - I'm going by what you presented at IETF91 a few months ago:
http://www.ietf.org/proceedings/91/slides/slides-91-6tisch-8.pdf
* IE regions are moving.  0x00-0x19 were unmanaged, now 0x01-0x18 are reserved
* macTsRxOffset change from 1120 to 1020us
* not allowed to use short addresses in nonce generation
Smart people are making arguments on both sides of these issues.  I would argue
that this means that these are not corrections, they are changes to an existing
standard without clear technical consensus.  The short address change is absolutely
a backward compatibility killer.

In addition, we had a long fight over changing IE format from {Length, Type, Value}
to {Type, Length, Value}.  The last I heard we lost that battle. That is absolutely a
backward compatibility killer.  Perhaps that one did finally get resolved in favor
of 4e, but the fact that such a change, with little to no practical value, would require
continuous debate over many meetings is a sign that backward compatibility is
not top of mind for a good part of the WG.  That's a real concern.

ksjp

On 3/30/2015 12:06 PM, Pat Kinney wrote:
> I disagree with both Kris' and Rene's objections.
> 
> Addressing Kris' objections first:
> - If the roll-up from 15.4e to  15.4-2015 were just corrections of real problems it would be a no-brainer.
> <PK> the element here is "just corrections", indeed there are corrections, but many non-TSCH and security corrections have been made as well
> - Unfortunately, there are numerous cases where IEEE members with "good ideas" have pushed for changes that have little or no practical value, but do require a re-write of existing code, and mandate non-interoperability between the existing 15.4e and the forthcoming 15.4-2015.
> <PK> '"good ideas" with little or no practical value' is a personal opinion, to which I disagree whole heartedly.'Requiring a rewrite of existing code and mandating non-interoperability between existing 15.4e and forthcoming 15.4-2015' is unfounded, the changes we have implemented have been critiqued for backward compatibility, I am not aware of any change that would make the two versions of devices non-interoperable. I ask that Kris quantify his statement with evidence.
> 
> Addressing Rene's objections:
> - To me, it is not a given that the revision effort of 802.15.4 that is currently on its way will automatically satisfy requirements 6TiSCH has.
> <PK> to what TSCH requirements does Rene refer? I ask that Rene to not critique without giving evidence
> - I am wondering how we would know, since so far technical changes have never been discussed/socialized within 6TiSCH itself (see also http://www.ietf.org/mail-archive/web/6tisch/current/msg02853.html). Anecdotal evidence regarding extensive changes makes me somewhat pessimistic here.
> <PK> the url provided by Rene merely restates his objections in the past, they absolutely have no evidence supporting them, e.g. "this does not necessarily mean they can speak for 6tisch's interests, at least not without consensus." I ask Rene again, what 6tisch interests with a consensus have been ignored or disregarded? Please stop referring to past innuendos but instead let's discuss specific technical questions
> - So, I am not in favor of implicit, blind trust; only in favor of explicit, verified trust. Unfortunately, this means I think the recommendation you put forward below is imprudent.
> <PK> I addressed the aspect of "the explicit verified trust" at the meeting in Dallas, the latest draft revision will be made publicly available at the start of the Sponsor Ballot which could start as early as 8 April 2015. Until then, I ask that anyone in the 6tisch group to address specific questions to this ML to which I can specifically reply.
> 
> Pat
> 
> Pat Kinney
> Kinney Consulting LLC
> IEEE 802.15 WG vice chair, TG chair
> ISA100.11a WG chair
> O: +1.847.960.3715
> [e-mail]
> 
> 
> 
> 
> 
> 
> On 30, Mar2015, at 13:22, Rene Struik <[e-mail]> wrote:
> 
> Hi Pascal:
> 
> I think the proper approach is that one investigates whether an updated version of a cross-referenced specification is suitable and, if so, one can adopt this.
> 
> To me, it is not a given that the revision effort of 802.15.4 that is currently on its way will automatically satisfy requirements 6TiSCH has. I am wondering how we would know, since so far technical changes have never been discussed/socialized within 6TiSCH itself (see also http://www.ietf.org/mail-archive/web/6tisch/current/msg02853.html). Anecdotal evidence regarding extensive changes makes me somewhat pessimistic here.
> 
> We should use a "trust but verify" approach here. Anything else would be imprudent. I think this more or less reiterates Subir Das's point.
> 
> So, I am not in favor of implicit, blind trust; only in favor of explicit, verified trust. Unfortunately, this means I think the recommendation you put forward below is imprudent.
> 
> As a final note:
> a) not sure why the 802.15.4e amendment would be incomplete. This seems to be in direct conflict with the note on page 1 of the 802.15.4e-2012 standard (NOTE—The editing instructions contained in this amendment define how to merge the material contained therein into the existing base standard and its amendments to form the comprehensive standard).
> b) Not sure how one can already predict now when the current revision work will be end and result in a revised standard. Assuming that this will be in 2015 (with sponsor ballot not having started yet) seems somewhat premature.
> 
> Rene
> 
> On 3/30/2015 11:23 AM, Pascal Thubert (pthubert) wrote:
>> Dear all:
>> 
>> Pat presented at the WG on Thursday his recommendation to remove the 'e' after IEEE802.15.4 in our current charter and WG Documents (slides at the end of http://www.ietf.org/proceedings/92/slides/slides-92-6tisch-2.pdf ).
>> 
>> The net effect would be that when a new version of the standard is published - 2015 should be available soon -, our normative references will implicitly pick that latest version and inherit the fixes that were made since then, as well as the additional PHYs on which 802.15.4 TSCH can operate.
>> 
>> Pat indicated that this procedure is the expected one when referring to IEEE documents. Subir noted that at the IETF we normally have reference on particular versions, and a change in an RFC is a new RFC thus a new reference, and the IEEE form of reference may create an issue with IETF practice. The chairs will need to validate this before proceeding.
>> 
>> On the question whether the change is desirable, Pat made the case that 15.4e is just an amendment, which is an incomplete reference, and that it yields some incorrectness that is now fixed in the upcoming 2015 version of 802.15.4.
>> All in all the group agreed that the change is desirable. We are now coming to the list to confirm the consensus. If you have an issue with removing the 'e' please speak up now.
>> 
>> Cheers,
>> 
>> Pascal and Thomas
>> 
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