The networks are also expected to have a
high node density in most cases. Here, node density refers to the number of
nodes in the communication range of a single node. High node density makes
the system more robust to routing and node failures, since each node has
several alternative paths to reach the sink. Thus sensor networks di?®er from
other wireless networks due to the scale at which the nodes are deployed in
the network.
3.3 Many-to-one Communication Paradigm
The primary objective of the nodes in a sensor network is to monitor a signal
of interest. These observations are then used by a decision-making center (sink
or a base station) to decide the future course of action. Thus data flows in two
directions in the network; upstream (many-to-one) in which sensor nodes send
their measurements to the sink, and downstream (one-to-many) in which the
sink sends queries or code-updates to the sensor nodes. However, the majority
of the tra?±c flows from the sensor nodes to the sink. This is unlike the Internet
where the traditional client-server communication paradigm results in most
of the tra?±c flowing from a single server to many clients, or in a peer-to-peer
network where the tra?±c flows between any two nodes of the network. Thus,
in general, there is no any-to-any communication, i.e., a sensor node does not
communicate with an arbitrary sensor node in the network (except during
packet forwarding).
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