Subject: [6lo] Iotdir early review of draft-ietf-6lo-deadline-time-02

From: Wesley Eddy <[email-masked]>
Date: Tue, 18 Sep 2018 21:32:39 -0700

Reviewer: Wesley Eddy
Review result: Ready with Issues

The draft is easily readable and can be understood and should be simple to
implement by someone working in the area.

I only have one technical issue that I think should definitely need to be
resolved, and a few small editorial comments.

Technical issues:

- The point of the D-bit is confusing.  It is supposed to indicate whether the
packet MUST be dropped when the deadline is exceeded.  However, if the D-bit is
zero, the document says that a 6LR "MAY" forward the packet anyways.  Since
this uses MAY rather than "MUST" or "MUST NOT", it seems like there should be
some example use case, scenario, or rationale for why an implementer would
choose one way or the other, or how they would include logic to make the
decision when the D-bit is 0.  Fundamentally though, I'm also unsure why a
sender would include a deadline and then set the D-bit to 0 ... is it maybe
something like they still want the packet to be delivered so that network
measurements of current latency or other properties can be measured using the
packet?  If the deadline is missed due to congestion/contention causing
increased delays, then it seems prudent to always drop the packet, in which
case the D-bit would not be needed.

Editorial comments:

- In Section 1, 2nd paragraph, it would probably be good to explain what an
elective RH is and define 6LoRHE as an elective 6LoRH here, before "6LoRHE" is
used in the Deadline-6LoRHE name.

- In Section 1, last paragraph, it would be good to add informative references
for the last two sentences mentioning Bluetooth and Wi-SUN work in this area.

- In Section 4, last paragraph, it might be worth mentioning for clarity that
there are also potentially long serialization delay and MAC layer contention
delays in some of the relevant network types.  These could dominate propagation
and queueing that are mentioned, in some feasible cases.

- The "Length of DT field" and "Length of OT field" descriptions seem a bit
light, although from the examples it is clear, but they could be replaced with
something more clear like "Length of DT field as an unsigned 3-bit integer,
encoding the length of the field in octets, minus one."

---

From: Lijo Thomas <[email-masked]>
Date: Sat, 22 Sep 2018 12:02:28 +0530 (IST)

Dear Wesley,

Thanks for your valuable comments.

Please find the inline answers (marked as LT >>) for your comments in the below
email.

Happy to receiver your further inputs ...

Thanks & Regards
Lijo Thomas

On September 19, 2018 at 10:02 AM Wesley Eddy <[email-masked]> wrote:
Reviewer: Wesley Eddy
 Review result: Ready with Issues

 Technical issues:

>> LT :  As you rightly noted, the primary reason for giving an option 0 for 'D'
>> bit is for making delay measurements,
>>                                                                                                                        and
>> also to perform packet delay analysis on the bottleneck segments that are
>> causing the deadline to exceed and take remedial action if possible.

Will the below additional text substantiate the usage of D bit set to 0 case:

" The usage of D bit set to 0  implies the packet MAY be forwarded on an
exception basis,
                                                                                                                                                      if
the forwarding node is NOT in a situation of constrained resource, and if there
are reasons
                                                                                                                                              to
suspect that downstream nodes might find it useful (delay measurements,
interpolations, etc.) "

Kindly let me know your inputs ..

 Editorial comments:

 - In Section 1, 2nd paragraph, it would probably be good to explain what an
   elective RH is and define 6LoRHE as an elective 6LoRH here, before "6LoRHE"
is
   used in the Deadline-6LoRHE name.

>> LT : Will update the draft with the corrections

>> LT :  Will put the informative references.

 - In Section 4, last paragraph, it might be worth mentioning for clarity that
   there are also potentially long serialization delay and MAC layer contention
   delays in some of the relevant network types. These could dominate
propagation
   and queueing that are mentioned, in some feasible cases.

>> LT : Nice suggestion, will update the draft.

>> LT :  Will modify the draft and make the corrections based on the inputs
>> provided.
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