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Re: [Roll] I-D Action: draft-ietf-roll-p2p-rpl-10 comments

Mukul Goyal <mukul@uwm.edu> Sat, 05 May 2012 14:34 UTC

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Date: Sat, 05 May 2012 09:34:15 -0500
From: Mukul Goyal <mukul@uwm.edu>
To: Federico Consoli <admin@ipv6it.org>
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Cc: roll@ietf.org
Subject: Re: [Roll] I-D Action: draft-ietf-roll-p2p-rpl-10 comments
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On the other hand, if Imin/K are set less conservatively, you might see too many DIOs generated. There is no silver bullet. No single setting would work well in all situations. We do provide some guidance on how to set trickle timer in Section 9.2 of the draft. The trickle parameter values in default configuration option are a conservative estimate based on the desire to avoid too many DIOs. If these settings are not OK for a particular deployment, well then the default configuration option should not be used. The connectivity variance you described is indeed a tricky situation and would require a tradeoff with the need to avoid generating too many DIOs. I imagine one possible solution could be to allow a node to set its k based on its position (rank) in the DAG (k increases as you move closer to the edge). But, again there might be cases where this (or any other fix) wont work.

Thanks
Mukul

----- Original Message -----
From: "Federico Consoli" <admin@ipv6it.org>
To: roll@ietf.org
Sent: Saturday, May 5, 2012 4:04:09 AM
Subject: [Roll]  I-D Action: draft-ietf-roll-p2p-rpl-10 comments

Hi,
I disagree with the default value of trickle timer, especially for 
Imin=6 and K=1.
If you got a dense network it could lead to a very long time to build DAG.

Eg. Suppose you got 2 node A, B.
Node A got about 15-20 neighbor
Node B got only A as a neighbor.

When node A receive its first DIO it resets trickle to Imin and it 
starts trickle timer. Since A got a lot of neighbor its probably receive 
another consistent DIO so it will suppress the DIO message and it will 
increase its Imin to 7. So if node A suppress 6-8 times its DIO node B 
will receive it after a long time. Finally if the link A-B got an ETX of 
2 or 3 (or more) this time doubles.

These situations are not uncommon, especially in the routers at the edge 
of dense networks.

-- 
Regards
Consoli Federico

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