On Sep 1, 2008, at 4:56 AM, Michiel Konstapel wrote: > Thanks for your input! Great to get feedback "from the source", as it > were. Warning: wall of text coming up.
<snip> I agree that the initial link quality should be 10 not 0; for some reason I think this fix is in the head? What we tend to see over time is that CTP settles on very good and stable links. A link that *doesn't* have bursts of losses will hold longer than one that does. This has advantages in that route stability leads to fewer loops and control traffic for route repair. The cost (transmissions/deliveries) continues to decrease even after hours, seemingly approaching an asymptotic value. The issue with a 1.5 threshold has come up before; Stephen at Berkeley noted that this means a node locking onto a 2-hop, ETX=2 route will never move back to a 1-hop, ETX=1 route. This assumes that the ETX=2 route never varies (unlikely, at the very least due to collisions and interference). If you imagine both routes do not have perfectly stable, but rather time-varying ETX values due to dynamics, then at some point you'll have ETX=1 and ETX=2.5, at which point the node will switch back. The probability that you'll get ETX=3.5 and ETX=2 is much lower than ETX=1 and ETX=2.5, so the node will spend much more time on the overall better route. This handwaving assumes a bunch of things, of course. The best thing to do is to examine, through traces, how often this edge case occurs and whether it matters. What's nice is that we've reached a level of instrumentation and data gathering that we can really begin to quantitatively evaluate subtle changes. Phil _______________________________________________ Tinyos-help mailing list [email protected] https://www.millennium.berkeley.edu/cgi-bin/mailman/listinfo/tinyos-help
