Re: [Roll] Clarification on the objective function

["Pascal Thubert (pthubert)" <pthubert at cisco.com>]

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. 
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