We have found that CTP is sensitive to short bursts of packet loss on otherwise good radio links (ETX 1.0 to 1.2) and found something that may be of interest. LinkEstimatorP uses an ALPHA parameter of 2 (actually 0.2) for decaying its exponential average of eetx:
void updateEETX(neighbor_table_entry_t *ne, uint16_t newEst) {
ne->eetx = (ALPHA * ne->eetx + (10 - ALPHA) * newEst)/10;
}
Written as it is, this means it takes 80% of the new estimate and 20% of
the old - is it possible that this was supposed to be the other way
around? We find that a short burst of lost packets will quickly increase
ETX to levels where CTP will select a new parent, which causes excessive
beaconing as CTP resets its beacon interval and other nodes start
switching parents as well.
Kind regards,
Michiel
Michiel Konstapel
Software Engineer
T: +31 (0)15 26 00 44 6
F: +31 (0)15 26 00 40 5
W: www.sownet.nl
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