In such scenarios,
the network needs to be supplied with an a priori desired path that
would serve as a ???nominal??? trajectory that the routing protocol will try to
adhere to, taking into account its own constraints such as power depletion
and node position.
Trajectory Based Forwarding (TBF) [16] is an on-demand type of routing
where the path from source to destination is defined by a set of discrete geographical
points called checkpoints (therefore the classification as trajectorycentric).
This method o?®ers the robustness and speed of on-demand routing
along with the reliability of path discovery based routing. In terms of ondemand
routing, the metric necessary to determine the next hop is only the
geographic location of the surrounding nodes and their associated power. This
information can be broadcast once and then re-broadcast every time the node
goes to sleep or moves. The path is defined a priori and the checkpoints are
broadcast from the sink.
Trajectory-centric protocols have very interesting features that can bring
benefits to dense sensor networks. Forwarding based on trajectories decouples
the path name from the path itself [16]. Route maintenance is virtually
free and una?®ected by mobility, node failure, or sleep modes as the path is
independent of the names of nodes involved in the forwarding. Flooding, discovery
and multicast can be implemented easily. It can work even without
the availability of a GPS on the nodes since a coordinate system with respect
to the source can be defined by locating only nodes in the neighborhood of
the intended trajectory.
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