Re: [Roll] Clarification on the objective function

[JP Vasseur <jvasseur at cisco.com>]

On Nov 10, 2009, at 2:45 AM, Pascal Thubert (pthubert) wrote:

> Hi Phil and Julien:
>
> For 1) agreed with Phil. Any node with rank less than self in the  
> DODAG
> iteration can be a parent.
>
> For 2) RPL has the concept of preferred parent to deal with this.
>
>
> The preferred parent determines the node rank whether the second  
> (not as
> good) parent is already seen or not.
> The second (not as good) parent does not influence the rank.

=> used as a back up (similarly to siblings)

> This is done to avoid greedy behaviors and to simplify the metrics
> inheritance.
>
>
> Pascal
>
> > -----Original Message-----
> > From: Philip Levis [mailto:pal at cs.stanford.edu]
> > Sent: lundi 9 novembre 2009 18:00
> > To: Julien Abeille (jabeille)
> > Cc: Pascal Thubert (pthubert); JP Vasseur (jvasseur); Mathilde Durvy
> (mdurvy); roll
> > Subject: Re: [Roll] Clarification on the objective function
> >
> >
> > On Nov 9, 2009, at 4:57 AM, Julien Abeille (jabeille) wrote:
> >
> > > Hi Pascal,
> > >
> > > just to be sure I understand:
> > > - I have a preferred parent at rank 1, my rank is 5, I receive a DIO
> > > for a parent rank 2, must i ignore it? I would say no as this node
> > > is useful as backup parent, but if i lose my preferred parent,
> > > choosing the backup as preferred will make my rank increase (this is
> > > ok because if i compute rank based on all parents, I would have to
> > > increase rank at reception of the second DIO anyway)
> > > - At boot time, I receive two DIOs (rank 1 and 2) before computing
> > > OCP. If I calculate rank based on preferred only, if at some point I
> > > would like to switch to the other parent, I will have to move down.
> > >
> > > Still I think it is preferable to calculate rank based on preferred
> > > only, but what do other think?
> > > Julien
> >
> > Julien,
> >
> > Question 1: In -04, you MUST process the DIO. Section 5.4.2.1:
> >
> > 	If the rank of SRC as reported in the DIO message is lesser
> >        than that of the node within the DAG, then the DIO message
> MUST
> >        be considered for further processing
> >
> > Question 2: The draft is unclear.
> >
> > Phil