Subject: Re: [Roll] proposal for DAOs in non-caching DODAGs

From: Mukul Goyal <[email-masked]>
Date: Wed, 31 Mar 2010 09:49:05 -0500 (CDT)

Richard

> To be more precise, a DIO may contain separate metric information for  
> upwards and downwards paths (i.e. directional cost metrics) if having  
> the DAG and DAO parents being different sets is desirable.   

[Richard] This makes no sense to me.  If you want to optimize two
different metrics, in this case the upward and downward
costs, you need two separate DODAGs.  While you can use two
different criteria for DIO parents and DAO parents, both
sets need to be parents as defined by the rank in the DIO.
The DODAG is going to optimize the metric that determines
the rank.  Another metric can be used to tweak the DAO
parent choice, but it only gets to pick between parents
chosen by the rank metric.

[Mukul] I think Jonathan was talking about sending both upwards and downwards aggregated/local values for a metric in a DIO. You will agree that these costs could be very different in two directions. Having these directional costs available in the DIO will remove the guess work involved in picking a DAO parent. I agree that both DIO parents and DAO parents are parents and a node's rank should be higher than that of any of its DIO/DAO parent. A rank is a loop avoidance mechanism. It can reflect the upwards costs if you want it to. But it need not.

Thanks
Mukul

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