Subject: Re: [Roll] determining downward routes at the root

From: Mukul Goyal <[email-masked]>
Date: Tue, 20 Jul 2010 11:40:13 -0500 (CDT)

Hi Pascal

I think, in the absence of any explanation in the text, there is a risk of misinterpretation.

So, this is my interpretation of how it will work:

Root needs to determine the source route to node N. Root starts with node N's DAO, finds its highest preference parent, adds it to the route and then repeats the procedure with this parent. This continues until the route is complete.

So, this is a greedy approach to route discovery. The underlying assumption seems to be that a more preferred parent is infinitely better for downwards routing than a less preferred parent.

Another possibility is to let the DAG root reverse the path control field and use it as link cost to determine shortest paths to a destination using dijkstra.

It seems to me that there needs to be some guidance, perhaps in the objective function, regarding how path control is to be used (for non-storing operation) and how would the root calculate the downwards routes.

Thanks
Mukul
----- Original Message -----
From: "Pascal Thubert (pthubert)" <[email-masked]>
To: "Mukul Goyal" <[email-masked]>, "roll" <[email-masked]>
Sent: Tuesday, July 20, 2010 6:26:00 AM
Subject: RE: [Roll] determining downward routes at the root

Hi Mukul:

This is a pretty classical recursive route lookup. Only the highest
preference 1hop route should show up so recursively the root will quite
naturally build the source route header. Routing protocols usually do
not describe such operation.

Do you think there is a risk of misinterpretation?
Would someone else please shime in?

Pascal

> -----Original Message-----
> From: [email-masked] [mailto:[email-masked]] On Behalf
Of
> Mukul Goyal
> Sent: Tuesday, July 20, 2010 11:25 AM
> To: roll
> Subject: [Roll] determining downward routes at the root
>
> I was wondering if it makes sense to add some text to the RPL draft
regarding
> how does a root, in non-storing LLN, determine the _shortest_ downward
> routes to different destinations using the "path control" values as
the (inverse)
> link costs.
>
> Thanks
> Mukul
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