As an LED lights up, the human participant strikes the corresponding key on the xylophone. Piezo sensors are attached to each xylophone, so that they are able to sense when a note is played on the other xylophone. The Arduino for the receiving computer senses the note and then converts it back into hexadecimal code. And when the second computer sends a return packet, the order of operations is reversed.

Characters are issued one every second, giving the network a throughput of one baud. Geiger used a simple pre-broadband legacy protocol called Slip to serialize the data with minimal overhead. Typically, it takes about 15 minutes to transmit a single packet at this rate -- if the volunteer is patient enough to complete a whole packet, and doesn't hit any wrong notes in the process. Such dedication and proficiency has turned out to be a rarity in trials, however. "Humans are really terrible interfaces," Geiger said. Geiger and his team ran two public demonstrations at the University of California.

From this project, Geiger has gained a newfound appreciation of the seven layer OSI (Open Systems Interconnection) model for computer communications. With OSI, each layer is encapsulated from the others, allowing new technologies to replace older ones without disrupting the system as a whole. In this exercise, humans operated layer 1, the physical layer, where the bits are physically moved from one system to another. To the two computers communicating, however, it made no difference that people were conveying the bits back and forth with their xylophones. "With a properly configured network interface and operating system, an application does not know -- and does not need to know -- the logistics of what is known as the physical layer," Geiger's .

The exercise also provided some insights into the field of Human-Computer Interaction (HCI), the focus of ACM's conference, Geiger said. It emulates a technique HCI specialists use to design interfaces called umwelt, which is a practice of imagining what the world must look like to the potential users of the interface.

This experiment allowed participants to get the feel for what it would be like to be a circuit. In fact, Geiger even put the xylophone players in black cardboard boxes to isolate them from their surroundings, where they could concentrate only on transmitting bits.