Hi, I would like to discuss about how the path cost is calculated from the cost of its arcs. Currently this path is accumulated with an addition. I think it's bizarre because we try to create the best path in term of ratio (msg received/msf sent). So the cost of a path should be proportional to the chance of a packet to reach the sink through this path, i.e. 1/q(a,b)*q(b,c) for the path (a,b,c), and not 1/q(a,b) + 1/q(b,c). (q = PRR(a,b)*PRR(b,a)).
I tried to find incoherent cases with this accumulation and I found this one : 3 motes : a, b and c (a is the sink). q(a,b) = 0.5 q(b,c) = 0.2 The cost of (a,b,c) should be 1/(0.5*0.2) = 10, but the effective cost is 1/0.5 + 1/0.2 = 7. (q(a,b,c) = 0.5*0.2 = 0.1). If we have cost(a,c) = 8, then q(a,c) = 1/8 = 0.125. We have q(a,c) best then q(a,b,c) but cost(a,c) > cost(a,b,c), and c choose a bad best parent/path (the path (a,b,c) instead of (a,c)). If I take ETX instead of EETX (10/q) it doesn't change this reasoning. I would like to know if I miss something, maybe there's a good reson to use the addition instead of multiplication to accumulate the cost path, I would like to understand... Regards, Rémi
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