Last Call Review of draft-ietf-lpwan-schc-over-sigfox-20
review-ietf-lpwan-schc-over-sigfox-20-genart-lc-davies-2023-01-04-00

I am the assigned Gen-ART reviewer for this draft. The General Area
Review Team (Gen-ART) reviews all IETF documents being processed
by the IESG for the IETF Chair.  Please treat these comments just
like any other last call comments.

For more information, please see the FAQ at

<https://trac.ietf.org/trac/gen/wiki/GenArtfaq>.

Document: draft-ietf-lpwan-schc-over-sigfox-20
Reviewer: Elwyn Davies
Review Date: 2023-01-04
IETF LC End Date: 2022-12-20
IESG Telechat date: 2023-01-05

Summary:
Not ready.  I notice that major edits have been done to this document since the
IESG reviews raised some serious Discuss points.  Aside from some serious
points about the scope of the profile(s) in this review and whether there are
multiple profiles involved, I think that the scope of the changes made deserve
working group level review to ensure that the changes are technically accurate.
I apologize for the late delivery of this review.  I contracted Covid during
the Last Call period and it has taken me some time to recover.

Major issues:

s1, para 4: It should be made explicit whether the document sets  out a single
set of parameters, etc., forming a single profile or whether variations are
available so that more than one profile is possible.  The word 'recommended'
implies that there could be variations.  If so how would an implementation/user
know which profile was in use.  It has been noted elsewhere in reviews that
there are several versions of the Sigfox specification mentioned on the web
page which  gives access to the [sigfox-spec].  Does this profile apply to all
versions of the specification?  If not how does a device know which profile is
used with which specification?  This comment reflects inpart a Comment point
raised by Roman Danyliw

s3.2:  This section states:

"Messages sent from the Device to the Network are delivered by the
   Sigfox network (NGW) to the Network SCHC C/D + F/R through a
   callback/API with the following information:

   *  Device ID

   *  Message Sequence Number

   *  Message Payload

   *  Message Timestamp

   *  Device Geolocation (optional)

   *  Received Signal Strength Indicator (RSSI) (optional)

   *  Device Temperature (optional)

   *  Device Battery Voltage (optional)"

As far as I can see, the [sigfox-spec] makes no mention of how or where the
timestamp, geolocation information, device temperature and battery voltage are
encoded and the format used. I take it Message Counter and Message Sequence are
related in some way.  How?

Minor issues:

Header: More than 5 authors are listed.  This may now have been approved.

s1: Before embarking on descriptions that refer to elements of the Sigfox
network infrastructure, the document should tell the reader where s/he can find
a definitive description of the elements. Referring to the relevant section of
RFC 8376 would be useful,  but a reference to a Sigfox document with an
overview of the system would be very useful.  The Sigfox Radio Specifications
document is at too detailed a level to cover this requirement.  [Aside: I found
this document very hard work!]

s2: The reader is also expected to be familiar with the Sigfox terminology.

s3.2, para 1:  "The uplink message size is 12 bytes in size.".  Firstly: Uplink
messages are variable in size depending on the requested payload.  The payload
can be up to 12 bytes. Secondly: This is the application level size.  Six bytes
of header are added in the link layer together with authentication if used. 
Further bytes are added in the physical layer.

s8.2: I think RFC8376 is normative as the terminology used there is required
knowledge.

Nits/editorial comments:

s1, para 1: s/on top of all/in conjunction with any of/

s1, para 2: s/a great level of/a considerable degree of/

s1, para 2: s/on top of/in conjunction with/

s1, para 3: 'worldwide network':  This is advertising speak.  Try 'a very wide
area network'

s1, para 3: s/recovery of lost messages/including recovery of lost messages/

s1, para 3: a/fragmentation/reassembly/allowing for fragmentation/reassembly of
messages/

s1, para 4: s/This set of parameters are also known as/The set of parameters
forms/

s3, Figure 1: For certainty, it would be useful to show the direction in which
Uplink and Downlink messages travel.

s3.2, para 1: s/space diversity/spatial diversity/

s3.3, last para: s/Downlink request flag/A Downlink request flag/

s3.3.1, para 2: s/which is signal by a specific the Fragment Compressed Number
(FCN)/which is signalled by a specific value of the Fragment Compressed Number
(FCN)/