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On Nov 9, 2009, at 10:32 AM, Julien Abeille (jabeille) wrote:
Phil, Are you in favor of computing rank based on all parents, or only preferred?
It's not clear to me what a "preferred" parent is. Is it the exact parent at time T? A node may wish to change which next hop it uses very quickly (albeit under constraints that keep the topology consistent). Jonathan Hui's IP layer does this: it chooses an alternate parent after three consecutive link delivery failures (no acks).
The way I see it, a node has a neighbor set, which is an unconstrained set of link-local neighboring nodes. Its parent set is a subset of its neighbor set, and these parents can be used arbitrarily (an implementation could just cycle through them for each transmission, if it wanted). The only time when a node has *a* parent is the instant it transmits a packet to a particular next hop.
Given this, Rank should be computed based on the parent set. I'd say that
A node MUST NOT advertise a Rank that is less than or equal to any member of its parent set.
Phil