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

[Lijo Thomas <[e-mail]>]

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 <[e-mail]> wrote:
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.

>> 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

 - 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.

>> 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.

- 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."


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