Re: [Roll] New Version Notification -draft-ietf-roll-minrank-hysteresis-of-07.txt

["Pascal Thubert (pthubert)" <[e-mail]>]

Phil:

It's not. 
If I switch a device with another from a different vendor I should
expect the new device to interact properly with existing devices and I
should expect globally a similar behavior in my network. 
That's what standards are for.

RPL 3.7.1 gives strong directions to avoid greediness. You may allow to
stray from that but that must be under control of the admin and you must
give strong recommendations for the default behavior.

Cheers,

Pascal

-----Original Message-----
From: Philip Levis [mailto:[e-mail]] 
Sent: lundi 9 avril 2012 17:46
To: Pascal Thubert (pthubert)
Cc: [e-mail]
Subject: Re: [Roll] New Version Notification
-draft-ietf-roll-minrank-hysteresis-of-07.txt

On Apr 8, 2012, at 10:00 AM, Pascal Thubert (pthubert) wrote:

> Phil:
> 
> It is an implementation decision as long as it does not lead to 
> interop issue or unwanted behavior, which is probably the case here.
> RFC 6550 demands that a node can't stray from the best Rank as 
> computed amongst parents by more than MaxRankIncrease.
> This 3 clauses do not seem to capture this that we are discussing do 
> not seem to capture this.
> With (my reading of) the text as it stands, it seems that the 
> implementation has all freedom to select parents and then is given 
> rules to compute a Rank.
> The resulting Rank could be anything if the parent set as no
constraint.
> 
> 
> In particular  " The largest  calculated Rank among paths through the 
> parent set, minus MaxRankIncrease" must be less that the Rank obtained

> from the preferred parent, not the final computed Rank.
> 
> 
> The node should:
> 1) Compute the Ranks form its parent set. 
> 2) Determine a preferred parent as resulting with the lowest Rank 
> (using the computation described in the previous paragraph)
> 3) Determine which parents generate a Rank that is between that lowest

> Rank and MaxRankIncrease
> 4) Pick a set of parents between those
> 
> What do you think?

This is an implementation decision. I can imagine other algorithms,
e.g., where if the best Rank and next best Rank differ by more than
MaxRankIncrease, the node chooses to advertise a worse Rank than the
preferred parent provides.

Phil