his states that, as the number of nodes on-board sensors, processor, memory, wireless increases, every node spends almost all of its time for- modem, and power supply. It is often abbreviated as warding packets of other nodes. From the energy point of node. When a node has only a single sensor on board, view, transmitting raw data to distant nodes is wasteful of the node is sometimes also referred to as a sensor, scarce resources. The diminishing wireless capacity creating some confusion. result can be somewhat mitigated by introducing mo- Network topology: A connectivity graph where nodes bility to nodes, if an application is delay-tolerant. are sensor nodes and edges are communication links. In a sensor network context, one can clearly do In a wireless network, the link represents a one-hop better. Since data from multiple sensors with over- connection, and the neighbors of a node are those lapping sensing regions is almost always correlated, one within the radio range of the node. can remove the redundant information in the data, Routing: The process of determining a network path through in-network aggregation and compression local from a packet source node to its destination. to the nodes that generate the data, before shipping it Date-centric: Approaches that name, route, or access to a remote node. In fact, it can be shown that the a piece of data via properties, such as physical loca- amount of nonredundant data that a network generates tion, that are external to a communication network. grows as O (12%N), assuming that the network is sam- This is to be contrasted with address-centric ap- pling a physical phenomenon with a prescribed accuracy proaches which use logical properties of nodes re- requirement. This is encouraging since the amount of lated to the network structure. CHAPTER 3.7 Wireless sensor networks Geographic routing: Routing of data based on geo- the overall system task and knowledge. For example, graphical attributes such as locations or regions. information utility of a piece of sensor dat