In 1991, Mark Weiser described his vision of an emerging world of pervasive, embedded computation. He predicted “a physical world that is richly and invisibly interwoven with sensors, actuators, displays, and computational elements, embedded seamlessly in the everyday objects of our lives and connected through a continuous network.” This vision is becoming a reality: the ever-increasing availability of inexpensive computation and storage has introduced computers into nearly every facet of our everyday lives, while a revolution in communications has brought high-bandwidth communications into our homes and offices. Wireless communications also has exploded, making digital services available nearly everywhere
