[Tinyos-devel] Re: CTP with -20dbm on Mirage

[Omprakash Gnawali]

On Dec 27, 2007 5:27 PM, Philip Levis <pal at cs.stanford.edu> wrote:
>
> On Dec 27, 2007, at 4:24 PM, Omprakash Gnawali wrote:
> >
> > I added  a new graph called goodcost-depth ratio which is the 4th
> > graph from the top of the page. The goodcost-depth ratio has
> > definitely increased with tx power of 5. This means the paths are
> > worse - it could be because there are no better paths or ctp does not
> > find better paths. What are these bad nodes? We can look at two places
> > - there is a graph called "Delivery ratio by node id". Looking at that
> > graph, many times the nodes that offer low delivery ratio with a5 are
> > different from the nodes that offer low delivery ratio with a6.
> > Looking at cumgoodcost(t), node 140 stands out. It is easy to see the
> > trend in goodcost using this node. It will be good to get a physical
> > explanation for why node 140 is special.
>
> Correct me if I'm wrong, but the goodcost-depth ratio is the average
> link ETX for a node across all of its packets? If that's true, yeah
> -- it looks like lower power forces CTP to use more intermediate
> links. That makes sense.

It is roughly that but it does not count the transmissions that did
not result in successful pkt delivery so we really want this number to
be closer to 1 if there are enough links to form a good tree even with
low tx power. It is alright to select intermediate links if there are
no good links. It will be good to confirm, if possible, there are not
enough good links to form a good tree with tx power of 5.

- om_p