Connecting the devices in our lives, from toasters to fitness devices, to each other and to the Internet is the fundamental principle of the Internet of Things (IoT). Enabling this connectivity requires at the very least a direct connection to the Internet, but often data is routed and processed at a local network stage before being passed to the Internet. Some sensor networks are not connected to the Internet at all, and their data is simply aggregated and displayed at a local aggregation point, such as a smartphone or PC. The topology of the sensor network depends largely on the overall system application: a personal area network may simply stream data from all sensors to a single central aggregator (star topology), whereas a home monitoring network may use a self-healing mesh topology. The different sensor topologies and the applications to which they are most suited are discussed in this chapter.As more and more devices are connected to the Internet, big data challenges emerge: volume, velocity, variety, and veracity. Sensor data is cheap to generate, but expensive to move, store, and manage. Not all data is useful. The sensor network, or more specifically the aggregator on the sensor network, has a key role in aggregating data: identifying which data should be presented to the user or a remote network and which data should be discarded. The earlier data is processed in the sensor lifecycle, the cheaper the overall system will be. Increasingly capable, low-power, low-cost devices are being developed for this edge-processing role. We discuss these aggregation devices in detail in this chapter.Managing large numbers of different sensors across a sensor network is a challenging task, particularly if the sensors are deployed in remote locations. Cloud-based sensor-network management tools are becoming increasingly popular. These tools provide real-time network status information, the ability to remotely change a sensor's configuration, and basic data storage and visualization. Many popular cloud-based services can be quickly integrated with popular sensor platforms, such as Arduino. Therefore, they are becoming a popular tool for the maker community and IoT enthusiasts. The most popular sensor-network management tools and their sensor interfaces are discussed and compared at the end of this chapter.
Sensor Network ComponentsA sensor network consists of a group of smart sensors that are wired or wirelessly connected to another smart sensor or to a common aggregator. In networking terminology, each component in the network that has a communications module is called a node. A node that generates data is called a source node, while a node that requests data is called a sink or sink node. A sink can be another sensor node on the network, a gateway to another larger network, or a local aggregator. A source node can report routine data, an alert, or maintenance data. The sensor network performs two key tasks: data gathering and data dissemination. Data gathering is term used to describe the capture and transfer of data...