Hubs
increase Net risk
By
Kimberly Patch,
Technology Research NewsThe Internet has much in common with air travel, according to researchers from Ohio State University. This does not bode well, considering how disruptive storms can be to the airlines.
The commercial Internet has shifted from its original distributed structure toward a hub-and-spoke topology similar to those the airlines use to plot routes, and that shift has made the network more vulnerable, said Tony Grubesic, an Ohio State researcher who is now an assistant professor of geography at the University of Cincinnati.
A handful of cities, including Los Angeles, New York City, Atlanta, Dallas and Chicago, have become central to the Internet and have many more backbone connections than other locations, said Grubesic. These cities are "in effect, acting as hub cities," he said. Chicago, for example, had 23 direct connections to other cities on the AT&T network in the year 2000, versus three for Salt Lake City.
Although the hub-and-spoke topology is cheaper to build, hubs make the network more vulnerable to attack in the same way bad weather in a major hub city can affect flights all over the country, said Grubesic. "Where Internet survivability is concerned, this type of network topology is not a particularly effective one because it forces large volumes of traffic through a handful of cities," he said. "If one of the major points of presence in a city should fail, [for example] the metropolitan area exchange in Dallas, traffic would be disrupted nationwide."
The original topology of the Internet was more distributed, and was designed to withstand failure and provide service under adverse conditions - even a nuclear attack.
As the Internet has grown, however, the competitive nature of the Internet backbone provider industry has caused many providers to shift to the more vulnerable hub-and-spoke system in search of the most economically efficient network topology, according to Grubesic.
The researchers' analysis showed the overall vulnerability of the hub-and-spoke system for 41 network backbone providers. The most susceptible networks have the greatest reliance on hub-and-spoke configurations. The networks most susceptible to disconnection are AT&T, GTE, and Multacom, which would suffer significant performance hits and leave many smaller spoke cities without service with the loss of any one of eight, seven or six of the 14 largest hubs, respectively, according to the analysis.
In contrast, there are 11 network providers that use network topologies that resemble a mesh rather than a hub and spokes; these providers are robust enough to survive the loss of any of the largest hubs. These mesh-like topologies are more expensive to construct, but clearly have advantages where survivability is concerned, according to Grubesic.
To carry out the study, the researchers integrated information about a large set of Internet backbone networks into a geographic information system. "This allowed us to simulate a wide range of Internet disruptions and failures [and] examine... the topological and spatial impacts simultaneously," said Grubesic.
The researchers simulated what would happen if there were a catastrophic failure of the Internet at a hub city or an equally important backbone link. "We simulated the failure of four things: complete loss of a node, or city; loss of a backbone [provider]; loss of a single network node; loss of selected backbone links," said Grubesic.
If an entire hub were knocked out, service to the city in question would be impossible for any backbone. This is a fairly improbable scenario, especially because providers tend to maintain multiple connections in large cities, according to Grubesic. It is a vulnerability, however.
In one portion of the results, the researchers simulated the availability of the network of one provider -- Multacom -- after a complete node failure.
The city of Washington is the most accessible node on the Multacom network. The researchers showed that if all connections into Tampa failed, Washington would lose access to Tampa plus one other city -- Miami. However, if all connections to New York failed, the ramifications for Washington would be much greater; Washington would lose access to New York, Chicago, Denver, San Jose, Portland and Seattle, according to Grubesic.
Worse, the simulation showed that if Atlanta, the most important node on the Multacom backbone, lost all its connections, Multacom communications would cease between Dallas, Los Angeles, Miami and Tampa and 10 other cities each, and between Chicago, Denver, New York, Portland, San Jose, Seattle and Washington and five other cities each.
This scenario is particularly problematic for spoke cities, which rely on the nearest hub.
The second scenario, the loss of a backbone provider, would leave cities serviced by a single provider completely without Internet service. Spoke cities would again be hard hit, according to Grubesic.
The third possibility, failure of a single network node within a city, is a smaller problem. Although this eliminates service to that node from a single provider, other backbones will remain, allowing traffic to continue, according to Grubesic.
But even a single network node failure would be problematic for spoke cities, because it effectively eliminates the delivery of all traffic destined for the node in question, said Grubesic. The large hubs, and cities served by several providers would do much better because they can reroute traffic.
In the fourth scenario, where select links in a network are severed, isolated nodes would lose service, but nodes that connect to more than one backbone would remain functional.
The methodology can also be applied to other types of networks, including critical infrastructure networks like electric, gas and oil, said Grubesic.
Two of the challenges in carrying out the study were creating code that simultaneously simulated node and link failure for a geographic information system, and developing intuitive ways to interpret the results, Grubesic said.
The researchers' analysis methods can be applied now to the Internet and other types of networks, said Grubesic. "One of our primary goals... was to provide a clear and understandable methodology for estimating the spatial impacts of node link failure for the Internet. This methodology can be revisited, duplicated and perhaps improved by other research teams interested in questions of Internet survivability," he said.
Grubesic's research colleagues were Morton E. O'Kelly and Alan T. Murray. The results are slated to be published in the February, 2003 issue of Telematics and Informatics. The research was funded by the National Science Foundation.
Timeline: Now
Funding: Government
TRN Categories: Internet; Computers and Society
Story Type: News
Related Elements: Technical paper, "A Geographic Perspective on Commercial Internet Survivability," Telematics and Informatics, February, 2003.
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January 1/8, 2003
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