Fig. 3.2 SmartSensor environment
The SmartSensor is a system composed of a group of potentially heterogeneous
wireless sensor networks, a set of gateway nodes organized in a hierarchy, and several
client applications (Fig. 3.2 ). Each WSN is connected to the infrastructure through
one gateway node. Gateway nodes communicate among them so that the Smart-
Sensor keeps a unified view on the resources provided by all WSNs connected to
the infrastructure. Such unified view is managed by the Programming and Execu-
tion Module (PEM) while the Sensor Integration Module (SIM) is responsible for
managing the resources of a single WSN.
The software components of the Sensor Integration Module are deployed and
executed in both the sensor nodes and the gateway nodes. PEMandWIMcomponents
execute only in the gateway nodes. Considering the traditional architecture of aWSN,
the gateway corresponds to the Sink node. Besides the software components of SIM,
PEM and WIM, a gateway node needs to implement the WSN radio protocol stack
(MAC and physical layers) in order to enable the communication with the sensor
nodes, thus acting as a bridge between the Internet protocols and WSN protocols.
Most of the current sensor platforms adopt IEEE 802.15.4 protocol (ZigBee [ 27 ]) to
The Sensor IntegrationModule includes, among other software components, those
responsible for the implementation of the HTTP protocol API, as well as drivers for
handling received requests and specific commands of each sensor platformconnected
to the infrastructure. The gateway is responsible for integrating WSNs in the Web,
extracting data from them, and providing such data to end users or client applications.
The use of a gateway node is ultimately required in spite of sensor nodes having or not
an embedded HTTP server, for the following reasons: (i) the protocol stack adopted