Re: [Roll] Fwd: I-D Action: draft-ietf-roll-rpl-observations-03.txt

"Pascal Thubert (pthubert)" <pthubert@cisco.com> Thu, 28 November 2019 15:25 UTC

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From: "Pascal Thubert (pthubert)" <pthubert@cisco.com>
To: Routing Over Low power and Lossy networks <roll@ietf.org>
Thread-Topic: [Roll] Fwd: I-D Action: draft-ietf-roll-rpl-observations-03.txt
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Date: Thu, 28 Nov 2019 15:24:58 +0000
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Subject: Re: [Roll] Fwd: I-D Action: draft-ietf-roll-rpl-observations-03.txt
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Hello Rahul

The text works. I’d have liked that it makes a distinction between resetting and restarting. The former acts on parameters the latter on a running timers.

Resetting means I<-Imin. That’s it.
Restarting the timer means an API call to the kernel timer services.
These are different things and it would be more clear if we separated them.

If I is not Imin then resetting means changing the value of I; this implies that the current running timer operates on wrong parameters and this may time out too late. The simple thing to do to solve this is to restart the timer based on the new parameters.

But if I is already set into Imin resetting it (to Imin) produces no effect. Which means that the running timer operates on the right parameters and doesn’t need to be restarted.


Regards,

Pascal

Le 28 nov. 2019 à 09:06, Rahul Jadhav <rahul.ietf@gmail.com>; a écrit :


Hi Pascal,

I have updated as follows. This clarifies the interpretation and then also explains specifically in context to multicast DIS/DIO operation.

"

5.  Interpreting Trickle Timer

   Trickle timer defines a mechanism to reset the timer.  Trickle timer
   reset is unlike regular periodic timers wherein the timer is simply
   reset to start again.  Reset of trickle timer implies resetting the
   trickle back to Imin and starting with a new interval as mentioned in
   Section 4.2 of [RFC6206].

|----|--------|----------------|--------------------------------| . . . . . .
 Imin   I2             I3                       I4                       I5

                     Figure 4: Trickle Timer Operation

   The above figure shows an example of trickle intervals.  An interval
   is double that of the previous interval size.  Section 4.2. of
   [RFC6206] states that,

   "If Trickle hears a transmission that is "inconsistent" and I is
   greater than Imin, it resets the Trickle timer.  To reset the timer,
   Trickle sets I to Imin and starts a new interval as in step 2.  If I
   is equal to Imin when Trickle hears an "inconsistent" transmission,
   Trickle does nothing.  Trickle can also reset its timer in response
   to external "events"."

   Thus if the trickle timer has advanced to subsequent intervals i.e.,
   >= I2, then a reset of trickle timer implies going back to Imin.
   However, if the trickle timer is currently in Imin and if it hears an
   inconsistent transmission then it does nothing.

   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.

   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.

"
https://github.com/roll-wg/rpl-observations/pull/8

Best,
Rahul

On Tue, 26 Nov 2019 at 22:31, Pascal Thubert (pthubert) <pthubert@cisco.com<mailto:pthubert@cisco.com>> wrote:
Hello Rahul :

I mean that if the spec says reset trickle and I is already Imin then the timer already operates within the bounds that are expected so it does not need to be restarted. Now if I was larger than Imin at the time of the reset then it was operating out of bounds and needs to be restarted to timeout earlier. Same if K changes, e.g., by configuration. The current timer operates with the wrong parameters and should be restarted.

Makes more sense?

Pascal

From: Roll <roll-bounces@ietf.org<mailto:roll-bounces@ietf.org>> On Behalf Of Rahul Jadhav
Sent: mardi 26 novembre 2019 15:25
To: Routing Over Low power and Lossy networks <roll@ietf.org<mailto:roll@ietf.org>>
Subject: Re: [Roll] Fwd: I-D Action: draft-ietf-roll-rpl-observations-03.txt

Hi Pascal,

On Tue, 26 Nov 2019 at 20:56, Pascal Thubert (pthubert) <pthubert@cisco.com<mailto:pthubert@cisco.com>> wrote:
Hello Rahul

I believe I undertand what you want to d but the text below is really unclear to me
“
  Implementations MUST not restart the trickle timer to the
  instantaneous value of I which could have been advanced over a period
  of time.
“
[RJ] ok. But I could not think of anything better. May be I should use asciiart and explain with an example. What do you think?

What I thought you’d write is that the trickle time needs only be restarted is one value I, K has changed, making the current run incompatible with the setting.
[RJ] This is unclear for me. Specifically "trickle time needs only be restarted is one value I, K has changed"


All the best

Pascal


From: Roll <roll-bounces@ietf.org<mailto:roll-bounces@ietf.org>> On Behalf Of Rahul Jadhav
Sent: mardi 26 novembre 2019 13:47
To: Routing Over Low power and Lossy networks <roll@ietf.org<mailto:roll@ietf.org>>
Subject: [Roll] Fwd: I-D Action: draft-ietf-roll-rpl-observations-03...txt

Hello All,

The update contains clarification regarding Trickle timer reset handling.

Regards,
Rahul
---------- Forwarded message ---------
From: <internet-drafts@ietf.org<mailto:internet-drafts@ietf.org>>
Date: Tue, 26 Nov 2019 at 20:42
Subject: [Roll] I-D Action: draft-ietf-roll-rpl-observations-03.txt
To: <i-d-announce@ietf.org<mailto:i-d-announce@ietf.org>>
Cc: <roll@ietf.org<mailto:roll@ietf.org>>



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-03.txt
        Pages           : 18
        Date            : 2019-11-26

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 are also htmlized versions available at:
https://tools.ietf.org/html/draft-ietf-roll-rpl-observations-03
https://datatracker.ietf.org/doc/html/draft-ietf-roll-rpl-observations-03

A diff from the previous version is available at:
https://www.ietf.org/rfcdiff?url2=draft-ietf-roll-rpl-observations-03


Please note that it may take a couple of minutes from the time of submission
until the htmlized version and diff are available at tools.ietf.org<http://tools.ietf.org>.

Internet-Drafts are also available by anonymous FTP at:
ftp://ftp...ietf.org/internet-drafts/<ftp://ftp.ietf.org/internet-drafts/>

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