[net2-wg] link estimator interface

[Omprakash Gnawali]

> > 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.

Without absolute values, it would be difficult to do
blacklisting. That is a real example.

> 
> 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.
> 

Agreed.