Re: [Roll] New Version Notification for draft-thubert-roll-asymlink-00.txt

Hi Pascal,

I agree that asymmetric links are challenging to establish a stable and optimal routing topology.

I strongly push the design of a mechanism that could enable to route in such conditions.

I think it is worth to flesh out a standard mechanism to address issues with asymmetrical links, as it is not really an exception in LLNs.

I'm sure many RPL implementations faced asymmetrical links, and each one has its own mechanism.
It may be great to gather our experiments and do it in a standard way.

BTW, it would also enable a safer and quicker behavior of parent selection, as DIO are not acknowledged (Link local multicast).

Your proposition seems good and simple because it just need a flag in the metric container.

I'm wondering about the overhead it would imply.
Would you need to manage 2 DAGs before coupling them ?

Cédric.

Le 17 oct. 2011 à 12:33, Pascal Thubert (pthubert) a écrit :

> Dear WG:
> 
> During the elaboration of RPL draft, RPL ticket #32 was opened to cover Asymmetric Links. Richard in particular suggested to "Add a flag to Routing Metric/Constraint to indicate whether the path metric represents the upward (flag = 0) or downward (flag = 1) metric.  The flag would only be meaningful for path metrics that are aggregations of potentially asymmetric link metrics, such as latency or link quality". 
> 
> The group did not express enough interest at the time to make that feature a core feature of the protocol. 
> 
> Still, there are specific cases of strongly asymmetrical links where an optimization would be useful when affordable. This popped up again recently during the bi-weekly discussion between the authors of the industrial applicability draft. So we decided that I should raise the question again to the group, as a new optimization. This draft suggested as we discussed long ago to make 2 DODAGs, one optimized for upwards traffic and one for downwards, and then couple them.
> 
> What do you think?
> 
> Pascal
> -----Original Message-----
> From: internet-drafts@ietf.org [mailto:internet-drafts@ietf.org] 
> Sent: lundi 17 octobre 2011 12:04
> To: Pascal Thubert (pthubert)
> Cc: Pascal Thubert (pthubert)
> Subject: New Version Notification for draft-thubert-roll-asymlink-00.txt
> 
> A new version of I-D, draft-thubert-roll-asymlink-00.txt has been successfully submitted by Pascal Thubert and posted to the IETF repository.
> 
> Filename:	 draft-thubert-roll-asymlink
> Revision:	 00
> Title:		 RPL adaptation for asymmetrical links
> Creation date:	 2011-10-17
> WG ID:		 Individual Submission
> Number of pages: 9
> 
> Abstract:
>   The Routing Protocol for Low Power and Lossy Networks defines a
>   generic Distance Vector protocol for Low Power and Lossy Networks,
>   many of which exhibit strongly asymmetrical characteristics.  This
>   draft proposes an extension for that optimizes RPL operations whereby
>   upwards and downwards direction-optimized RPL instances are
>   associated.
> 
> 
> 
> 
> 
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