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

Mukul Goyal <mukul@uwm.edu> Sat, 26 May 2012 06:00 UTC

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Date: Sat, 26 May 2012 01:00:53 -0500
From: Mukul Goyal <mukul@uwm.edu>
To: Michael Richardson <mcr+ietf@sandelman.ca>
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Cc: roll@ietf.org
Subject: Re: [Roll] knowing which multiple metrics matter: MRHOF related questions
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Hi Michael

Here is my take:

[MCR]
- 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.

[Mukul]
Yes, the nodes in a DODAG have to use the same metrics. Otherwise, it is not possible for an OF to map the aggregated (from root till this node) values of the metrics to a rank.

[MCR] 
- 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.
[Mukul]
Not sure what does the first sentence mean. About the second, different sets of metrics can certainly coexist in the same RPL instance. An RPL Instance is associated with a particular OF but different DODAGs in the RPL Instance can certainly use different routing metrics.

Thanks
Mukul

----- Original Message -----
From: "Michael Richardson" <mcr+ietf@sandelman.ca>
To: "Pascal Thubert (pthubert)" <pthubert@cisco.com>
Cc: roll@ietf.org
Sent: Friday, May 25, 2012 2:29:49 PM
Subject: Re: [Roll] knowing which multiple metrics matter: MRHOF related	questions


>>>>> "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.

- 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.


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


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