The OSDL Protocol provides a way for sensors, triggers, actuators and controllers to communicate with each other using existing, established technologies.
Where possible technology is utilised to minimise the amount of configuration needed for sensor networks. As an example zero-configuration networking can be used with sensors and a universal recorder. The universal recorder will query any sensors it can identify on the network, and sensors can be added or removed without configuration of the recorder.
In real-world settings multiple sensors, triggers,a ctuators and/or controllers may be present on a single device ('node'). Each node has a node descriptor file that details what services it provides for the sensor network.
Sensors are devices that make a measurement of a variable (e.g. Temperature, humidity, distance to an object). In the OSDL model sensors are passive devices: they respond to a query when requested.
Whereas sensors are considered as passive devices (waiting until queried to provide data), triggers actively notify the network that an event has occurred (e.g. a laser trip wire has been blocked, humidity is now above 80%). Other nodes can register for notifications from trigger nodes.
Actuator nodes have an interface that can be queried for an action to be performed. An example of an actuator is the OSDL Camera Trap node, that can trigger a camera by either the wired or infra-red shutter release. Querying the camera interface of the node causes the camera to be triggered. Actuators allow the sensor network to respond to observations.
A controller node does not advertise any interfaces on the network. Controller nodes are used to query sensors, activate actuators and respond to triggers.