Re: [Roll] I-D Action: draft-ietf-roll-rpl-observations-06.txt

Philip Levis <pal@cs.stanford.edu> Mon, 14 June 2021 19:23 UTC

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Subject: Re: [Roll] I-D Action: draft-ietf-roll-rpl-observations-06.txt
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I was looking at this draft and wanted to clarify a little of the text, in Section 5:

   "In context to multicast DIS/DIO operation, this implies that if the
   DIO trickle timer is already at Imin and if the node hears a
   multicast DIS, then the timer does nothing.  It MUST NOT reset the
   timer again in this case.”

The first paragraph at first seemed redundant with the Trickle specification: if it is already at Imin, it does nothing, which means it does not reset the timer. Or is the ambiguity about resetting the timer? If so, then I think this refinement is correct. External events should be able to be considered inconsistencies, not hard-reset the timer. In retrospect, the sentence 

  Trickle can also reset its timer in response to external “events"

Perhaps could have been

  External events can also cause Trickle to act as if it has detected an inconsistency.

So I think this paragraph makes sense, but the way to characterize it is that a multicast DIS resets the timer only if I > Imin.

The next paragraph I’m a little more confused about:
   
   "An implementation MUST never restart the timer within an interval.
   For e.g., in the above figure, if the timer is in interval I2, the
   implementation MUST never restart the timer to the beginning of the
   current interval i.e., I2.  If the timer is in interval T2 and if the
   reset is to be done then the interval is set back to Imin.  If the
   timer is already in Imin, then the reset should do nothing.”

Trickle never “restarts” a timer. It can reset a timer to Imin, but not restart the timer within a particular interval. Under what circumstances would an implementation “restart” a timer to the beginning of the current interval? 

Phil



> On Jun 3, 2021, at 5:32 AM, internet-drafts@ietf.org wrote:
> 
> 
> A New Internet-Draft is available from the on-line Internet-Drafts directories.
> This draft is a work item of the Routing Over Low power and Lossy networks WG of the IETF.
> 
>        Title           : RPL Observations
>        Authors         : Rahul Arvind Jadhav
>                          Rabi Narayan Sahoo
>                          Yuefeng Wu
> 	Filename        : draft-ietf-roll-rpl-observations-06.txt
> 	Pages           : 20
> 	Date            : 2021-06-03
> 
> Abstract:
>   This document describes RPL protocol design issues, various
>   observations and possible consequences of the design and
>   implementation choices.
> 
> 
> The IETF datatracker status page for this draft is:
> https://datatracker.ietf.org/doc/draft-ietf-roll-rpl-observations/
> 
> There is also an htmlized version available at:
> https://datatracker.ietf.org/doc/html/draft-ietf-roll-rpl-observations-06
> 
> A diff from the previous version is available at:
> https://www.ietf.org/rfcdiff?url2=draft-ietf-roll-rpl-observations-06
> 
> 
> Internet-Drafts are also available by anonymous FTP at:
> ftp://ftp.ietf.org/internet-drafts/
> 
> 
> _______________________________________________
> Roll mailing list
> Roll@ietf.org
> https://www.ietf.org/mailman/listinfo/roll

———————
Philip Levis (he/him)
Associate Professor, Computer Science and Electrical Engineering
Faculty Director, lab64 Maker Space
Stanford University
http://csl.stanford.edu/~pal