Following figure shows model of wireless sensor networks.

A wireless sensor network consists of thousands of low-cost nodes which could either have a fixed location or be randomly deployed to monitor the environment.

Sensors usually communicate with each other using a multi hop approach.

A base station links the sensor network to another network (like a gateway) to disseminate the data sensed for further processing. Base stations have enhanced capabilities over simple sensor nodes since they must do complex data processing.

One of the biggest problems of sensor networks is power consumption, which is greatly affected by communication between nodes. To solve this, aggregation points are introduced in the network. This reduces the total number of messages exchanged between nodes and saves some energy.

Aggregation points are regular nodes that receive data from neighboring nodes, perform some kind of processing, and then forward the filtered data to the next hop.

Sensor nodes are organized into clusters, each cluster having a “cluster head” as the leader. The communication within a cluster must travel through the cluster head, which is then forwarded to a neighboring cluster head until it reaches its destination, the base station.

The design of the sensor network as described by Figure 1 is influenced by following factors:

• Fault Tolerance- Due to the failure of sensor nodes.
• Scalability- Due to increase in the number of sensor nodes.
• Production Costs - Due to large number of sensor nodes, the cost of system network increases.
• Operating Environment- Sensor nodes are densely deployed either very close to or directly inside the phenomenon to be observed.
• Sensor Network Topology- Deploying a high number of nodes densely requires careful handling of topological maintenance.
• Hardware Constraints- A sensor node is made up of four basic components as a sensing unit, a processing unit, a transceiver unit, and a power unit which generates Hardware Constraints.
• Transmission Media- To enable the global operation of sensor networks, the chosen transmission medium must be available worldwide.
• Power Consumption- The energy in data communication involves both data transmission and reception. The wireless sensor node can only be equipped with a limited power source. So need to increase battery lifetime .