Subject: [Roll] what link/routing metrics are people using with RPL?

From: Omprakash Gnawali <[email-masked]>
Date: Sat, 19 Feb 2011 08:36:00 -0800

Working on MRHOF, I would like to know if people are using metrics
other than ETX. In the implementations I am familiar with, ETX or
something similar to ETX is being used.

If people are using any other metric, it will be great to know how
they are computing the rank based on those metrics. Are they
converting them into rank with the way suggested in MRHOF draft? If
there are better ways to do that conversion, it will be great to
incorporate those ideas into MRHOF.

If people who are building real networks have not found other metrics
useful in their implementations, that is useful to know as well.

- om_p

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From: Mariano Alvira <[email-masked]>
Date: Sat, 19 Feb 2011 14:03:49 -0500

> useful in their implementations, that is useful to know as well.

I've done testing with PATHDR which is an LQI based method. I've
detailed my tests here:

    http://devl.org/pipermail/mc1322x/2010-October/000548.html

My tests are with Econotags running Contiki arranged in a 23-node
test-grid with attenuated antennas; this lets me do multi-hop testing
in a compact space.

I converted to rank by mapping the path probability of delivery to
rank (high probability equals low rank). I can point out the relevant
lines in my patches if you want more information.

I find LQI based metrics interesting as they do not need link level
probing.

I've since implemented 802.15.4 acknowledgements and can now start
testing with ETX.

-Mar.

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From: Philip Levis <[email-masked]>
Date: Sat, 19 Feb 2011 11:11:32 -0800

> I find LQI based metrics interesting as they do not need link level

Not true in the presence of external interference.

Phil

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From: Mariano Alvira <[email-masked]>
Date: Sat, 19 Feb 2011 14:24:36 -0500

> Not true in the presence of external interference.

I should clarify that my main interest at the time was that it was
much easier to implement an LQI based metric rather that to get the
802.15.4 autoacks working on the mc13224v. But now that I have that
working, I suppose it doesn't make much difference to me.

-Mar.

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From: Philip Levis <[email-masked]>
Date: Sat, 19 Feb 2011 11:46:29 -0800

> working, I suppose it doesn't make much difference to me.

Sure -- physical layer information on chip error rates is a very quick and easy way to obtain not terrible link estimates that mostly work. But generally you want a protocol to do better than "not terrible" and be more dependable than "mostly."

Phil

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From: Mariano Alvira <[email-masked]>
Date: Sat, 19 Feb 2011 15:05:23 -0500

On Sat, Feb 19, 2011 at 11:46:29AM -0800, Philip Levis wrote:
> 
>
> But generally you want a protocol to do better than "not terrible" and be more dependable than "mostly."
>

Yes definitely! Although part of that is to also make these radios
work better than "not terrible" and more dependable than "mostly" ---
which can take quite an effort. But I'm glad; from what you are saying
it sounds like the time I'm investing now in autoacking will lead to
major benefits from all the layers.

-Mar.

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From: Omprakash Gnawali <[email-masked]>
Date: Sat, 19 Feb 2011 12:55:51 -0800

> major benefits from all the layers.

Good to hear you are considering implementing RPL based on ETX metric.
It will be great if you could read the MRHOF draft and let me know if
there is something confusing from an implementer's perspective. Also,
if you would implement ETX routing differently, that is a good
feedback as well.

Here is the link to the current draft:
http://tools.ietf.org/html/draft-gnawali-roll-minrank-hysteresis-of-02

Thanks.

- om_p

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From: Omprakash Gnawali <[email-masked]>
Date: Sat, 19 Feb 2011 15:14:35 -0800

> http://tools.ietf.org/html/draft-gnawali-roll-minrank-hysteresis-of-02

The correct link is this one:
http://tools.ietf.org/id/draft-ietf-roll-minrank-hysteresis-of-00.txt

Sorry about that.

- om_p

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From: Richard Kelsey <[email-masked]>
Date: Mon, 21 Feb 2011 10:00:05 -0500

> working, I suppose it doesn't make much difference to me.

Which metric you use and how you determine the values are
two different things.  There's nothing wrong with using
LQI values to estimate ETX.  For example, you may need a
a value for a link which hasn't seen much traffic.  Or you
may not have 802.15.4 autoacks working :-).

                                  -Richard Kelsey