Re: [Roll] knowing which multiple metrics matter: MRHOF related questions

Mukul Goyal <mukul@uwm.edu> Tue, 05 June 2012 08:09 UTC

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Date: Tue, 5 Jun 2012 03:09:49 -0500 (CDT)
From: Mukul Goyal <mukul@uwm.edu>
To: "Pascal Thubert (pthubert)" <pthubert@cisco.com>
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Subject: Re: [Roll] knowing which multiple metrics matter: MRHOF related questions
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Hi Pascal

>I'm curious: where did you get the second point from?

The mapping from (RPLInstanceID, DODAGID) pair to (OF, metrics) pair comes from my understanding that the root (the provider of DODAGID) decides what metrics to use.

>No, you can't switch metric as you switch DODAGID within an instance. Because nodes can move (jump is the word in the spec) from a DODAG to the next, and need to compare apple to apple when they do so...

That makes sense. I stand corrected.

Cheers
Mukul


-----Original Message-----
From: Mukul Goyal [mailto:mukul@uwm.edu] 
Sent: mardi 5 juin 2012 09:12
To: Pascal Thubert (pthubert)
Cc: roll@ietf.org; Michael Richardson
Subject: Re: [Roll] knowing which multiple metrics matter: MRHOF related questions

Hi Pascal

So, what you are suggesting is that an RPLInstanceID is associated with (OF, metrics) pair and not just OF? This would not be in accordance with RC 6550, which associates an RPLInstanceID with an OF. My understanding is:

1) An RPLInstanceID is associated with an OF.
2) (RPLInstanceID, DODAGID) pair is associated with (OF, metrics) pair.

Thanks
Mukul

----- Original Message -----
From: "Pascal Thubert (pthubert)" <pthubert@cisco.com>
To: "Mukul Goyal" <mukul@uwm.edu>
Cc: roll@ietf.org, "Michael Richardson" <mcr+ietf@sandelman.ca>
Sent: Tuesday, June 5, 2012 1:52:09 AM
Subject: RE: [Roll] knowing which multiple metrics matter: MRHOF related questions

Hi Ralph:

Well, no. Whether an instance is a single DODAG (one root) or multiple, the instance has to be homogeneous. 
This is because nodes will move from one DODAG to the next when the environment requires the change, and the rules must not change. 

Cheers,

Pascal


-----Original Message-----
From: Mukul Goyal [mailto:mukul@uwm.edu] 
Sent: mardi 5 juin 2012 08:34
To: Pascal Thubert (pthubert)
Cc: roll@ietf.org; Michael Richardson
Subject: Re: [Roll] knowing which multiple metrics matter: MRHOF related questions

Hi Pascal

>An instance can use multiple metrics bound by some logic. But those metrics and that logic must be identical throughout the instance. A different (set of) metric means a different OF even if MRHOF is behind both.

Could you please explain. This is not how I understand the relationship among an RPL Instance, an OF and metrics to be. As per my understanding, there is one OF associated with an RPL Instance and the metrics in use are chosen by the root. Accordingly, an RPL Instance _can_ have different DODAGIDs using different sets of metrics.

Thanks
Mukul 




----- Original Message -----
From: "Pascal Thubert (pthubert)" <pthubert@cisco.com>
To: "Michael Richardson" <mcr+ietf@sandelman.ca>
Cc: roll@ietf.org
Sent: Monday, May 28, 2012 2:04:59 PM
Subject: Re: [Roll] knowing which multiple metrics matter: MRHOF related questions

Hello Micheal

>>>>> "Pascal" == Pascal Thubert <(pthubert)" <pthubert@cisco.com>> writes:
    Pascal> I think RPL does not want to take party there. The OF is a
    Pascal> piece of logic to tie metrics and policies together.  

My question is:

- do the nodes of a DODAG have to use the same metrics to pick a parent,
  (and if so, how do they agree)
  I think that they do not, so long as they use an algorithm (such as
  MRHOF) which has certain properties.

[Pascal]  The current spec requires that all players of an instance play by the same rule, that is same OF, in order to guarantee the expected result. 
The goal there was deeper than the OF, like same OF with same parameterization. MRHOF is generic and allows various incarnations, depending in the metrics; all those incarnations are to be seen as different OFs WRT to RPL 's uniqueness rule.

Note that this rule is not for looplessness, the Rank would assure that anyway.


- if we had multiple RPL instances in an LLN, using different metrics,
  then we would have multiple RPL Instances and DODAGs.  The different
  set of metrics would not co-exist in the same RPL Instance.

[Pascal] I think we agree. An instance can use multiple metrics bound by some logic. But those metrics and that logic must be identical throughout the instance. 
A different (set of) metric means a different OF even if MRHOF is behind both.

Cheers,

Pascal

-- 
Michael Richardson <mcr+IETF@sandelman.ca>ca>, Sandelman Software Works 
IETF ROLL WG co-chair.    http://datatracker.ietf.org/wg/roll/charter/

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