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Previous approaches for computing duplicate-sensitive aggregates in wireless sensor networks have used a tree topology, in order to conserve energy and to avoid double-counting sensor readings. However, a tree topology is not robust against node and communication failures, which are common in sensor networks. In this article, we present synopsis diffusion , a general framework for achieving significantly more accurate and reliable answers by combining energy-efficient multipath routing schemes with techniques that avoid double-counting. Synopsis diffusion avoids double-counting through the use of order- and duplicate-insensitive (ODI) synopses that compactly summarize intermediate results during in-network aggregation. We provide a surprisingly simple test that makes it easy to check the correctness of an ODI synopsis. We show that the properties of ODI synopses and synopsis diffusion create implicit acknowledgments of packet delivery. Such acknowledgments enable energy-efficient adaptation of message routes to dynamic message loss conditions, even in the presence of asymmetric links. Finally, we illustrate using extensive simulations the significant robustness, accuracy, and energy-efficiency improvements of synopsis diffusion over previous approaches.

To date, sensor-network research has largely been defined by the design of algorithms and systems to cope with the severe resource constraints of tiny battery-powered sensors that use wireless communication (for example, slow CPUs, low-bitrate radios, and scarce energy). Such sensor networks are distributed over a single, contiguous communication domain. They use simple sensors that provide time series of single numerical measurements, such as temperature, pressure, light level, and so on. Researchers have developed spe-Today's common computing hardware-Internet connected desktop PCs and inexpensive, commodity off-the-shelf sensors such as Webcams-is an ideal platform for a worldwide sensor web. IrisNet provides a software infrastructure for this platform that lets users query globally distributed collections of high-bit-rate sensors powerfully and efficiently.

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