ITU‐T's Technical Reports and Specifications 251 of the roads, the air pollution, the behavior of criminals or those attending sporting, cultural events and entertainment. 2.3.2.1 System Architecture for Wireless Sensor Networks The emerging field of wireless sensor networks combines sensing, computation, and communication into a single tiny device. Through advanced mesh networking protocols, these devices form a sea of connectivity that extends the reach of cyberspace out into the physical world. As water flows to fill every room of a submerged ship, the mesh networking connectivity will seek out and exploit any possible communication path by hopping data from node to node in search of its destination. While the capabilities of any single device are minimal, the composition of hundreds of devices offers radical new technological possibilities. The power of wireless sensor networks lies in the ability to deploy large numbers of tiny nodes that assemble and configure themselves. Usage scenarios for these devices range from real‐time tracking or monitoring of environmental conditions, to ubiquitous computing environments, in situ monitoring of the health of structures or equipment, among others. While often referred to as wireless sensor networks, they can also control actuators that extend control from cyberspace into the physical world. The concept of wireless sensor networks is based on a simple equation: However, actually combining sensors, radios, and CPU's into an effective wireless sensor network requires a detailed understanding of both capabilities and limitations of each of the underlying hardware components, as well as a detailed understanding of modern networking technologies and distributed systems theory. Each individual node must be designed to provide the set of primitives necessary to synthesize the interconnected web that will emerge as they are deployed, while meeting strict requirements of size, cost and power consumption. A core challenge is to map the overall system requirements down to individual device capabilities, requirements and actions. To make the wireless sensor network vision a reality, an architecture that synthesizes the envisioned applications out of the underlying hardware capabilities must be developed. 2.3.2.2 Sensor network application classes The three application classes, which have been selected are: environmental data collection, security monitoring, and sensor node tracking. It is believed that the majority of wireless sensor network deployments will fall into one of these class templates. Environmental Data Collection An environmental data collection application is to collect several sensor readings from a set of points in an environment over a period of time in order to detect trends and interdependencies. The idea is to collect data from hundreds of points spread throughout the area and then to analyze the data offline. At the network level, the environmental data collection application is characterized by having a large number of nodes continually sensing and transmitting data back to a set of base stations that store the data using traditional methods. These networks generally require very low data rates and extremely long lifetimes. In typical usage scenario, the nodes will be evenly distributed over an outdoor environment. This distance between adjacent nodes will be minimal yet the distance across the entire network will be significant.