Net
traffic mimics earthquakes
By
Kimberly Patch,
Technology Research NewsEarthquakes and the Internet may seem very different, but they do have one thing in common. They're both complex systems whose behavior is currently very difficult to predict.
Seismologists, statistical physicists and complex systems scientists around the world have long studied the ways the earth's many fault-lines interact with each other and the slow-moving tectonic plates that underlie the earth's crust in hopes of eventually figuring out ahead of time when and where earthquakes could occur.
Meanwhile, as the Internet has grown, computer scientists have studied the Net's structure and the ebbs and flows of its traffic in order to make network travel more efficient.
Complex system science, however, is still very much in its infancy, according to Dion Weatherley, a geophysicist at the University of Queensland in Australia. "There is no comprehensive 'complex systems theory' as yet," he said. "Scientists are gathering observations at an incredible rate, but... no one has managed to comprehend all these observations within a single theoretical framework."
Researchers from Tsukuba and Nihon universities in Japan may have uncovered a clue. They have shown that the self-organizing behavior of bits traveling down the Internet's communications lines shares some mathematical characteristics with the self-organizing behavior of the many cracks, or faults, in the earth's crust. "Although earthquakes and the Internet are apparently very different, they exhibit similar behaviors," said Sumiyoshi Abe, an associate professor of physics at University of Tsukuba in Japan.
Recent research into the Internet's structure has proved that the network has a scale-free, or power law nature, meaning it naturally organizes so that a few sites, or nodes have many links to other nodes, and the vast majority of nodes have only a few links. The discovery of this Internet structural trait "reminded me of the scale-free natures of earthquakes and financial markets," said Abe.
Self-organizing complex systems all have certain properties in common. The systems have a large number of individual elements, these elements interact in ways that affect nearby elements and in other ways that affect all of the elements in the system, and the system's behavior cannot be predicted simply by studying the individual elements and their interactions, according to Weatherley.
In the case of earthquakes, each fault represents an individual element, said Weatherley. "An earthquake along any given fault changes the pressure on surrounding faults, either promoting or inhibiting earthquakes of those faults," he said. At the same time, the motion of the earth's tectonic plates increases the pressure on all faults within the plate's region. "This is a global interaction," he said.
In the case of the Internet, each site is connected to the whole through servers, which host web pages, and routers, which coordinate traffic. The servers and routers themselves also form a hierarchical clustering structure, said Abe.
To find connections between Internet traffic patterns and earthquake behavior, the researchers measured minute changes in digital traffic by sending a series of signals from one computer to a site on the Internet and back.
The simple ping signals were emitted every second and traveled through 10 different routers before the signals eventually reached the destination computer. The researchers were able to measure frequent changes in Internet congestion by measuring the time it took a series of signals to complete a round trip.
The results showed that the Internet, like the earth's network of faults, exhibits criticality -- a condition of sudden and drastic change. "Sudden drastic congestion leads to a large value of the round trip time of the ping signal, which is identified with a main shock," said Abe. The researchers referred to these sudden, drastic traffic changes as Internetquakes.
Criticality exists whenever there is a phase transition. It happens, for example, when water suddenly turns to ice as it reaches 0 degrees Celsius. "Nowadays, this concept is employed in a wider sense for complex systems," said Abe.
The traffic snapshots showed that the Internet was constantly changing on two very different time scales. The longer events were user sessions on the net, which typically lasted an hour. The short quake events lasted about one tenth of a second.
The two-tiered timing resembles seismic activity, Abe said. Faults build up energy over a time-scale of many years, then release it as an earthquake over a few seconds.
Earthquakes follow the Gutenberg-Richter law, which says that the frequency of earthquakes corresponds to their magnitude. Specifically, the logarithm, or exponent, of the cumulative frequency of earthquakes is proportional to their magnitude. The researchers found that the Internetquakes followed similar mathematics: the round trip time, which represented the magnitude of the Internetquake, corresponded in the same way to the frequency of the quakes, according to Abe.
The researchers' experiments also showed similar mathematics between Internet activity and earthquake aftershock activity, said Abe. "We have also discovered the Omori law, known for aftershocks in seismology, [is true for] Internetquakes," he said. Omori's law describes the timing of earthquake aftershocks, and is also true of financial market crashes. Omori's law could be universal for complex systems, according to Abe.
The researchers are working to eventually use the Internetquake measurements to monitor the general health of Internet traffic, Abe said. "The network is healthy as long as it exhibits the scale-free nature, which is essential for the system to be robust against random errors, breakdowns and attacks," he said.
They are also continuing to compare earthquakes and Internet traffic activity in order to better understand and possibly predict catastrophic behaviors, said Abe. The study of Internetquakes could eventually shed new light on earthquakes, he said.
The Internet offers a big advantage to complex system researchers. It is much easier to trace traffic interactions over the communications lines that make up the Internet than to trace networks of fault patterns in the earth. The researchers' experiments were relatively simple, although they required a sizable amount of computer power to analyze large numbers of signals.
In contrast, there are considerable timing and logistics challenges in measuring faults. "Earthquakes involve processes occurring over a very broad range of spatial and temporal scales, from microns and seconds to thousands of kilometers and many hundreds of years," said Weatherley.
Even more problematic, "the majority of the processes involved are not directly measurable because they occur at great depths within the earth's crust -- typically more than five kilometers deep and up to... 600 kilometers deep," Weatherley said. "Due to the lack of observational data, progress in developing a comprehensive scientific theory of earthquakes has been greatly hampered and accurate predictions of earthquakes cannot be made," he said.
Whether the self-organizing properties of Internet traffic and the earth's crust truly follow the same mathematical laws is still an open question, said Weatherley. "The power-law distribution of round-trip times is certainly evidence that the Internet is a self-organizing complex system," he said. However, "evidence for a link between earthquakes and Internet traffic flow is not convincing," Weatherley said.
The researchers need to show "much more clearly that there are similarities between interacting fault systems and the Internet traffic flow interactions in order to claim that studying these 'Internetquakes' can provide insight into earthquakes," said Weatherley.
The close monitoring of Internetquake patterns may eventually contribute to making the Internet more efficient, said Abe. "We expect that further study in this direction will allow us to control or optimize the network behavior," he said. These methods could be ready to optimize real networks like the Internet in about 10 years, he said.
The researchers are also continuing to investigate similarities among earthquakes, the Internet, and also financial market crashes, said Abe. "It would appear that earthquakes, Internetquakes and financial market crashes are all fundamentally a manifestation of the same type of complex systems," he said.
Abe's research colleague was Norikazu Suzuki. The research was funded by University of Tsukuba and Nihon University.
Timeline: 10 years
Funding: University
TRN Categories: Applied Technology; Internet; Physics
Story Type: News
Related Elements: Technical paper, "Gutenberg-Richter Law for Internet Quakes," posted at the arXiv physics preprint archive at arXiv.org/abs/cond-mat/ ; Technical paper, "Omori's law in the Internet traffic," posted at the arXiv physics preprint archive at arxiv.org/PS_cache/cond-mat/pdf/0206/0206453.pdf
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August 21/28, 2002
Page One
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