[core] RobW comments on draft-ietf-core-senml-more-units-04

["Rob Wilton (rwilton)" <[e-mail]>]

Hi Carsten,

I'm providing some comments as an incoming Ops and Mgmt AD.

I found this document well written but think that it may be helpful to highlight the protocol usage of secondary units earlier in the document, i.e. in the introduction.

My understanding is that this document introduces both extra primary unit names, and also a new concept of secondary unit names, which I presume came about from deployment considerations.

Comments:

  1.  As per above, I think that it would be useful to add a comment in the introduction about how secondary units could be used.  E.g. may be extend



"The document also defines a registry for secondary Unit names that

   cannot be in SenML's main registry as they are derived by linear

   transformation from units already in that registry."



with the sentence "Although SenML version 10 [RFC8428] does not allow for the direct use of secondary units, they are planned to be supported via the use of SenML protocol extensions, such as [I-D.bormann-core-senml-versions]."


  1.  The introduction introduces the term "primary Unit names", but then doesn't refer to them using this term in the rest of the document.  It might be helpful if the title of section 2 was changed from "New Units" to "New primary Units", and the description could be changed from "... assign new units ..." to "... assign new primary unit names ...".



  1.  My reading of the "3. Rationale" section is that it relates to the new primary units, rather than secondary units.  The structure of the document might be clearer if this was made a subsection of the section 2 rather than its own top level section.



  1.  I would suggest renaming the section 4 title from "New Registry" to "New Registry for Secondary Units".





  1.  Regarding section 4 on secondary units:
     *   I observe that these are not using a generalized mechanism of using SI prefixes for scaling, but propose a separate custom mapping instead, which in some cases are just making use of SI prefixes.  I presume that there is a good reason for not wanting to generically use SI prefixes, perhaps for a bit more homogeneity in the scaling factors, but it might be helpful for the document to explain the rationale behind this.
     *   I note that you have similar units but with different scaling factors (e.g. KiB, GB, Mbit/s, MB/s).  Do we anticipate other scaling factors of these units?  E.g. if MB was requested as a secondary unit, then would that be added?  Would it make sense to define any more of these common scaling factors now?
     *   I also note that the names of some of the secondary units would overlap with SI prefixes (e.g. "min") for minutes.  This is okay, but would likely be an annoyance if it was ever desirable to use SI prefixes in a generic way.
     *   I wasn't sure whether "h" is really a great shorthand for hour, I would have gone for "hr" instead, but perhaps this is already widely used elsewhere?

Regards,
Rob