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

Agree with Pascal - for information there was a discussion about 2 years on the subject matter and there was a consensus
not to try to either mix metrics/constraints (which IMO is the right thing to do even if it leads to sub-optimality or disconnected
areas) or try to make use of default metrics.

On May 28, 2012, at 12:04 PM, Pascal Thubert (pthubert) wrote:

> 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>, Sandelman Software Works 
> IETF ROLL WG co-chair.    http://datatracker.ietf.org/wg/roll/charter/
> 
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