The nodes forward
and replicate the collected information among several nodes, until one
of them is able to deliver the information to the sink node. Two kinds
of approaches are possible, either (i) a flooding-based approach, or (ii) a
history-based approach. In the flooding-based approach, every data packet
at any node is forwarded to, and replicated at, all the nodes that come
into its communication range. In the history-based approach, each node
is assigned a hierarchy level based on its past success in forwarding the
data to the sink. This hierarchy level is nothing but the routing state
27 Chapter 1 Design of Large-scale Sensor Networks
Aravind Iyer et al.
of the node. Whenever a node comes close to a sink, its hierarchy level
is increased, and its hierarchy level is decreased over time whenever it
remains out of the range of the sink. Nodes forward packets to a neighbor
with the highest hierarchy level in their communication range. This is
similar to the tier-based routing scheme in [26].
2. Dual Radio Design: In order to monitor the vast habitat of the zebras,
the field researchers use a mobile sink (or base station) which can be driven
around the area non-intrusively. In order to avoid direct human contact,
the ZebraNet collars use long-range radios to communicate with the mobile
sink, so that the data can be collected from afar. However a long-range
radio requires considerably more power than a short-range radio.
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