The two important operations of a WSN are data dissemination
(send data/queries from sinks to sensor nodes) and data gathering
(send sensed data from sensor nodes to the sinks).
There are two types of sensor data collection: event-driven and demanddriven.
In the event-driven type, the reporting process is triggered by one
or more sensor nodes which detect an event and report it to the monitoring
station. In the demand-driven type, the reporting process is initiated by the
monitoring station and sensor nodes send their data in response to an explicit
request. A forest fire monitoring system is event-driven, whereas an inventory
control system is demand-driven. A hybrid system can operate on both types,
event and demand-driven.
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Although WSNs share some characteristics with traditional wireless networks
(such as cellular, Bluetooth and ad hoc networks), they di?®er from them
in the following aspects:
1. Energy conservation is of primary interest in WSNs. Sensors are battery
powered, and their batteries are usually neither replaceable nor rechargeable.
Energy resources might not be the main concern in the other networks,
where maintaining a certain Quality of Service (QoS) might be, for
example, the primary goal.
2. Sensor nodes might not have unique identifiers. Communication is datacentric,
where queries might be addressed to sensors satisfying certain
properties or to other sensors sensing certain parameter values.
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