Mutli-Layer Architecture
LUSTER’s architecture is composed of several layers,shown in Figure 1.
Figure 1: LUSTER's hierarchical architecture.
The sensor node layer is responsible for gathering, aggregating, and transmitting the measurement data. The report rate and sensor selection are configurable remotely using the SenQ sensor network query system. Communication among nodes in the cluster uses a noval TDMA MAC protocol, LiteTDMA,
The storage layer transparently blankets the sensor layer, collecting and filtering the data reported by sensor nodes without initiating any communication to them. The configuration specifies the data filtering and collection policies for each storage node, alleviating congestion internal to the storage hardware due to the flash memory delays. Reliability is provided through redundant coverage: each sensor node is monitored by at least two storage nodes. The configuration and the number of storage nodes are subject to application requirements for the fault tolerance required and cost limitations.
Above the storage layer is the delay-tolerant networking (DTN) component of the system. This consists of a base mote (denoted BM in Figure 1) attached to a stargate acting as a gateway between the IEEE 802.15.4 and IEEE 802.11 networks. This component uses DTN techniques to increase reliablity, particularly when connections to the gateway or the back-end server are lost.
The data monitored by the WSN is accessible over the Internet by connecting to the LUSTER back-end server. The server stores the incoming WSN data stream to a database and also issues data queries to the WSN as a DTN component detects losses.
Using a web browser, a web client can request and view historical data as well as the last captured “almost real time” data from the back-end server. Web pages are generated from HTML templates, in which the WSN data, including the sensor readings, are embedded in the HTML as custom tags. This allows for a user-centric customizable web interface that is specific to the chosen application.