After receiving the migration request, the new root broadcasts the reconf message.
A node receiving the reconf message re-broadcasts the message and attaches
its location and the cost of sending a packet to the new root. Nodes receiv-
344 Kai-Wei Fan, Sha Liu, and Prasun Sinha
ing the reconf message change their parent to the node with minimum energy
cost of sending a packet to the new root.
DCTC can also use other reconfiguration schemes to reduce the broadcasting
overhead in reconfiguration. The first one is based on grid structure. Instead of
flooding the reconf messages, the reconf message are only broadcast within the
grid, and are sent to neighboring grid heads. The neighboring grid heads broadcast
the reconf to their grids, and forward it to their neighboring grid heads. The
reconf message sent to neighboring grid heads contains the location and cost of
each node in the current grid. Nodes receiving the broadcast reconf message find
the parent according to this information, and therefore can construct a minimized
cost tree to the new root.
The second approach is used when only some nodes in the tree need to be reconfigured
[9], named interception-based reconfiguration. As shown in Figure 9,
only nodes between lines L1 and L2 are required to be reconfigured to change
their parent, and therefore reduce the cost of sending packets to the new root.
Since only a portion of the nodes need to be reconfigured, the overhead of broadcasting
or propagating reconf is reduced.
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