FOR Chris Chafe, the Internet is one giant musical instrument. By listening to the sounds it makes, he can tell you a lot about the health and strength of Internet connections. This will be music to the ears of those developing the next generation of interactive Internet technologies, like telesurgery, which need constant, reliable connections.
Telesurgery involves a surgeon using video screens to guide a remote robot arm to perform intricate operations. The robot and patient could be on the other side of the world, so the patient鈥檚 life depends on constant and reliable connections.
To check the quality of an Internet connection, engineers 鈥減ing鈥� a data packet to a remote computer, which bounces it back like an echo. This reveals the latency of the connection, or how long it takes for a round trip, and the variation of this over time is known as the jitter. But pinging cannot reveal the detailed subsecond behaviour of the jitter, and this is the timescale that is important in interactive applications like telemedicine.
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Chafe, a cellist and director of the Center for Computer Research in Music and Acoustics at Stanford University in California, wondered if variations in jitter could be converted into a musical form. A musician can easily hear small changes in the tuning of a guitar string, so Chafe decided to model Internet connections as guitar strings 鈥� twanging them to reveal subtle characteristics missed by pinging.
Plucking a guitar string sets up standing waves of a certain frequency, determined by the length and tension of the string. Tighten or loosen the string, and you change the frequency and hence the pitch of the note.
To simulate a string being plucked, Chafe and his team repeatedly sent a short sound pulse across a connection.
The time a pulse took to make the round trip depended on the state of the network. Say a pulse arrived at one end every 10 milliseconds. When fed into a loudspeaker and if the connection was good, this would emit a synthesised note of about 100 hertz 鈥� around an octave-and-a-half below middle C. The longer the transmission time, the lower the pitch of the note produced.
This gives a qualitative way of monitoring an Internet connection. Sudden loss of sound can reveal a break in the network connection or missing packets of data. 鈥淚t鈥檚 like having your CD player hiccup, or an MP3 player that stalls,鈥� says Chafe. Most important, the sound accurately reveals the jitter. If the latency varies over time, so does the pitch. 鈥淢usically speaking that would be like pitch bends, or vibrato,鈥� he says.
Chafe reckons the technique could be used as an audible check of the health of a network connection before embarking on critical telesurgery, where minute changes in network delay could be dangerous. He also speculates that his technique could help monitor the complex array of network connections on the Grid, the nascent network of academic supercomputers designed to provide massive computing power for tackling some of science鈥檚 upcoming big problems.
But simulating a guitar string wouldn鈥檛 be suitable for a two-dimensional network like that described by the Grid. Instead, says Chafe, you would need to simulate a stretched membrane, such as a drum skin.