 to each other as often as we would like them to. to a service station to enable just-in-time maintenance. Figure 3.7-7 Distributed video sensor networks for traffic and security applications. Upper figures: Networked cameras and other sensors could be used to monitor traffic flow to reduce congestion, track vehicles on city streets for traffic violations, or detect illegal activities around critical infrastructure such as airports. Lower figure: PARC video sensor network prototype uses in-network intelligence to decide what events to pay attention to and what to ignore, thus reducing the amount of information the network must collect and transport in order to support high-level monitoring applications. Wireless sensor networks CHAPTER 3.7 They can use the wireless connection to download data generated per node scales as O logN which is music and movies while waiting at a gas station. For some within the per-node throughput constraint derived by of these applications, the crucial difference lies in the Gupta and Kumar. On the other hand, instead of ap- real-time flow of information. Point-to-point routing as- plying data compression techniques to samples after sistance or road safety application requires access to up- they are collected, nodes can be more selective in what to-date or even instantaneous traffic data. data to generate or communicate. For energy- When sensors are used to guard critical infrastructure constrained and multiuser decentralized systems, it such as power plants or airports, they can provide becomes critical to carefully select the sensor nodes a virtual enclosure around the facilities to guard against that participate in a sensor collaboration, balancing the unauthorized intrusion. Unlike existing security systems information contribution of each against its resource that require human personnel to watch video feeds consumption or potential utility for other users. We use around the clock and pick out "unusual" events, which is the term collaborative signal and information processing clea