QoS in Sensor Networks

Quality of service required for different applications in sensor networks can be different. Some may require more precise and accurate information some may require less. Some applications might not tolerate any delay in notification after the detection of event and some may tolerate the delay. Some applications may monitor a large area with more number of active sensors and some applications might monitor only small area with less number of active sensors.

In sensor network the importance is on collective data delivery rather than packet form a single node, because in sensor network many sensor nodes produce similar data. So in sensor network terms such as collective latency, collective bandwidth usage, collective packet loss, collective information throughput come into picture.
Collective latency is the time between, the first packet related to an event is received by the sink and last packet related to that event is received at the sink, no matter which node produced the data. Collective bandwidth is the bandwidth required to report an event to the sink by sensor nodes al together. Collective packet loss is the number of packets lost al together during reporting of an event.
Any QoS mechanism introduced for WSN should be very simple, it should not be, computationally complex, time consuming, requiring large amount of memory. Because the sensor nodes are energy, memory constrained and sensor nodes do not use very high end processors also.

QoS support in sensor network should consider the fact that, event driven sensor networks are characterized by long periods of silence, when there are no events detected and small periods where large amount of traffic is produced, when any event is detected. And all the data produced are generally destined to sink, so traffic form nodes to sink will very large. So the QoS has to support this unbalanced traffic.

The probability of having redundant data is quite large in sensor networks, so the redundant data should be reduced as much as possible may be data aggregation. But one has to consider the delay involved and complexities involved in data aggregation and take a decision.

Sensor networks are very dynamic; there are high chances of, node failures, link failures, node mobility and node state transitions. So QoS support for sensor network should consider all the above factors.

The number of sensor nodes in sensor network is very large, probability of addition of nodes is also quite high, and so any sensor network application should be scalable.There are different types of data supported by the sensor networks QoS provided should support all different types of data.