[net2-wg] link estimator interface

[Joe Polastre]

> If I write a routing protocol that uses a certain threshold to switch
> from one path to another, then we would need some standard on what a
> change of 2 means. For, ETX, 1.5 is a huge change but for a
> reliability estimator that returns an estimate in the range [1,100], 2
> is 2%. If there is a standard, I would not have to configure my
> routing protocol when I go from one estimator to the next.

I was asking for a concrete example, not a hypothetical.

In all of the protocols in TinyOS 1.x, a relative value is used (is
this path >25% better than my current path?).  Using absolute units
seems extremely dangerous.

> Yes and this is the approach in the LQI estimator in TinyOS too but I
> am not aware of a way to derive ETX from LQI or a function of LQI. I
> have seen some statistics but they seem to be valid for some specific
> settings.

It is an approximation.  Anything you do is going to be an
approximation because you cannot 100% accurately predict ETX.

-Joe