Subject: [Roll] Node Energy Measuring Stick

From: "Colin O'Flynn" <[email-masked]>
Date: Thu, 23 Sep 2010 11:00:50 +0200

Hello,

As the previous thread on link energy somewhat split into multiple
discussions, I'd like to bring what I think is an important point to a
separate thread. So far only JP has chimed in on this discussion but if I'm
wrong I'd at least like to hear it from more than one person ;-)

The proposed energy metrics in the metrics-09 measures battery power as a
relative scale of "desired lifetime" to "current estimated lifetime". This
is good since it allows you to specify a non-replaceable node has e.g. a 10
year desired lifetime.

What this misses is some way to advertise the capacity of the battery. This
is important as it is impossible to know with the current metric until after
you start using the node if it is a car battery or a button coin cell.

I would propose the node energy takes into account the cost of carrying some
arbitrarily defined route. For example use the same metric (estimated
lifetime/desired lifetime) but have the estimated lifetime include
"estimated lifetime while carrying route". The arbitrary route will need to
be defined. Ideally it would somehow reflect the actual usage, but in
reality it might need to just be something like "sending a RPL DIO every
hour".

If this needs to be studied more it could simply be left to another/outside
document to define how this "example usage" is used. I think even having a
very simple estimated usage would be a huge improvement though as I there is
no way to know what the incremental cost of adding a route to the node will
be until you actually add it with the current proposal. 

Regards,

    -Colin O'Flynn

---

From: Richard Kelsey <[email-masked]>
Date: Thu, 23 Sep 2010 10:03:07 -0400

> From: "Colin O'Flynn" <[email-masked]>
> Date: Thu, 23 Sep 2010 11:00:50 +0200
> 

An 'available bandwidth' metric works for this.  For a
battery powered device you know the desired lifetime, the
amount of energy in the battery, and how much of this will
be consumed by the device itself.  The leftover energy,
divided by the desired lifetime and the cost of sending and
receiving, gives the bandwidth the device can donate to the
network.  This works for energy scavenging devices as well,
assuming that the scavenging rate is predictable.

                                 -Richard Kelsey

---

From: "Colin O'Flynn" <[email-masked]>
Date: Sat, 25 Sep 2010 11:56:23 +0200

Hi Richard,

This makes sense, I assume you mean to make use of the "throughput"
metric/constraint?

There would thus be a best practice to always use the throughput metric with
the node energy metric?

My understanding is thus the node energy metric provides a relative measure
of current power consumption vs. available power, and cannot be used to
decide the best route from an energy perspective. It can only be used as a
reactive measure to change a route that is using too much power. The
"throughput" metric is the metric providing information about creating a
route initially. Is this the desired result?

If so I think it would be important to explicitly mention this limitation to
prevent possible misuse of the node energy metric. 

Regards,

  -Colin

-----Original Message-----
From: Richard Kelsey [mailto:[email-masked]] 
Sent: September 23, 2010 4:03 PM
To: Colin O'Flynn
Cc: [email-masked]
Subject: Re: [Roll] Node Energy Measuring Stick

                                 -Richard Kelsey