[Tinyos-devel] Re: from longer CTP/LQI experiments

[Omprakash Gnawali]

On Dec 24, 2007 8:10 AM, Rodrigo Fonseca <rfonseca at cs.berkeley.edu> wrote:
> Hi Om,
>
> the results look coherent to me, and it seems that because there were
> very few failures, alpha doesn't really matter as the inputs to the
> EWMA are almost always the same.
> It's interesting from the graphs to look at the settling time of the
> network across the runs, from the goodcost over time graphs
> (http://enl.usc.edu/~om_p/net2/ctp4bitle/mirage-12212007/goodcostt.html)
>
> This is just qualitative, by looking at node 74 (the black checkered square)
>
> a5   300s
> a6 1300s
> a7  900s
> a7b 1100s
> a9   4000s
>
> At alpha 9, it takes a much longer time for the node to settle to a
> good path, as the estimator is much more resilient to change. On
> TutorNet, however, the agility of the estimator kills on lower alphas.
>
> Another interesting observation stems from the comparison between the
> goodcost(t) versus the thl(t) graphs. Take for example a6. THL is
> always low, meaning that the high goodcost is due to retransmissions.
> This is especially true in the beginning, when most nodes seem to
> choose very short paths that are not so great (low THL, high
> goodcost). Later they choose slightly longer paths with higher THL but
> much lower cost (good links with few retransmissions). On a6, at
> around 4000 seconds, there is a sharp rise in THL with a small rise in
> goodcost, meaning that longer paths were chosen due to some network
> phenomenon, but these were still fairly good (not so many
> retransmissions).
>
> From the THL graphs one can conclude that there is little evidence of
> persistent loops.

I plotted the loop events over time. The graphs are called cumloopevents(t) and
they are at the bottom of these two pages:
http://enl.usc.edu/~om_p/net2/ctp4bitle/mirage-12212007/figures.html
http://enl.usc.edu/~om_p/net2/ctp4bitle/figures.html

On Tutornet, larger alphas lead to fewer loops but on Mirage a5 has the fewest
loops while a9 has the most loops. But again, maybe not enough data. One trend
that is clear on both the sets: fewer loop incidents over time. On
Tutornet one can
just follow the a9 line to appreciate this. On Mirage, each experiment
ran for about
7200 s. If the line is truncated at t<7200, that means, there were no more loops
after the truncation point: a7, for example, truncates shortly after
1000s, that means,
the curve would be flat from approx. 1100 to 7200.

- om_p