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physical layer specified by the IEEE Std. 802.15.4 and introduces the network layer for
different topologies. It also provides a framework for application-layer development.
1.3 WSN Architecture
A sensor network typically consists of a collection of low-cost, low-powered sensor
nodes distributed in an ad-hoc fashion. Each of these networks has one or more sink
nodes or base stations, which is usually a resource-abundant computer with sufficient
storage, computing, and communication capabilities (Figure 1.1). These sink nodes
send queries or commands to their respective sensor nodes, which then collaborate with
each other to accomplish the given task. In addition, the sink nodes act as a gateway
between the sensor network and the outside network (Internet or cellular network).
A typical sensor node is equipped with the actual sensing equipment for data aggre-
gation, embedded microcontroller for instantaneous processing of data, and a radio
transceiver for digital communication. Usually, nodes communicate over a short dis-
tance and use a wireless medium for all communications. Each sensor node senses
data from its surrounding environment and sends this captured data to its sink node.
Generally, the data or control packets from the sending node travel in a hop-by-hop
fashion through every intermediate sensor node to reach the sink node (Figure 1.2).
Figure 1.1. Wireless Sensor Network
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