Please be aware that the SAS developments are currently discontinued in favour of the Sensor Event Service (SES). This new service interface enhances the SAS by adding new functionalities such as advanced filter capabilities.
The Sensor Alert Service dispatches alerts via XMPP (extensible messaging and presence protocol). Users follow a two step process. First thing to do is to define the alert condition, step two is to join the corresponding MultiUserChat (MUC). This framework provides software for sources (sensors and nodes that generate alerts), sinks (clients for receiving alerts and subscribing to alerts), and a web service part, which allows the discovery of available sensors by means of the OGC GetCapabilities interface.
The Sensor Alert Service allows sensor nodes to advertise and publish observational data or its descriptive metadata repsectively. It acts as a registry providing information about available sensor systems and real time access to its observation data. The SAS currently dispatches alerts via XMPP (extensible messaging and presence protocol) and optionally via other transport protocols (supported by communication gateways like WNS, for example).
The SAS workflow is described in the following figure: