Since forwarded packets also transmit position information, the number
of packets required to keep the routing information up to date is limited.
In the case of sensor networks, since the destination, or sink, is often stationary,
the destination node (sink) is set and only the source nodes change.
Therefore, routes to the sink will have many common nodes in the neighborhood
of the sink node. These nodes will be used often for routing and therefore
may die out faster than other nodes, causing routing to be switched to alter-
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nate neighboring nodes. Nodes which are farther from the sink and are not a
source of data will be less likely to be included in a data path. Regardless of
the position or frequency of use of a node, all nodes in the network will keep
up to date information about location received either when packets are forwarded
or from the periodic updates. Thus, for the nodes which are not often
used as relays, this information can be considered an unnecessary overhead.
MECN [20], SMECN [10], GAF [32], and GEAR [30] are other examples
of location-centric protocols.
3.4 Trajectory-Centric Routing
With the objective of securely forwarding data in a sensor network, a preferred
trajectory could be traced a priori. This is particularly true in problems where
obstacle avoidance is necessary to secure the routed information.
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