The 511 Building is a low-rise, concrete structure that is easy to overlook.

Located across from the Metrodome on 11th Avenue S., the one-time Control Data Business and Technology Center building has a featureless exterior devoid of signage, and is largely without windows. The Minnesota Vikings apparently thought the building was so unimportant that the organization briefly considered tearing it down to make way for the new football stadium.

That all changed with the threat of a lawsuit by the building's owner, Timeshare Systems, and the public disclosure of the building's actual purpose: It is Minnesota's largest Internet communications hub. Converging on the 511 Building are about 70 different data networks, ranging from AT&T and Verizon to Bemidji's Paul Bunyan Telecom.

Inside the building, pulses of laser light send hundreds of trillions of data bits surging from one network to the next every second. Fiber-optic cables beneath 5th and 6th Streets, the nearby light-rail tracks and Interstate 94 carry data from the 511 Building to the ends of the Earth. And back. It's all made possible by Xcel Energy's Elliot Park Substation across 5th Street, where two power grids converge to provide the building with enough electricity to power a small Minnesota city. (The two separate electric grids ensure continued power, should one of them go down.)

Varun Kharbanda, one of the owners of Timeshare Systems, doesn't offer a value for the 511 Building and downplays the company's earlier threat to sue the Vikings in order to save the facility.

"We knew once we had a discussion, they would agree" not to tear down the 511 Building, Kharbanda said.

The facility is one of a group of Internet data centers that sprouted around the nation in the 1990s dot-com boom. Called "carrier hotels" (telecommunications companies are often called carriers), they were needed to interconnect the huge fiber networks being built to support Internet traffic.

"No one telecommunications provider can deliver it all, so they have to work together," said Mike Hemphill, the Minneapolis general manager for Cologix, a Denver-based network interconnection firm that, with about 100 Minneapolis workers, is a major tenant in the 511 Building. "This is a place that allows them to do that. We're an enabler."

Today, carrier hotels are key interconnection points for the World Wide Web. For smaller telephone or cable companies, carrier hotels provide a way to connect to such major Internet carriers as AT&T, Verizon, Level 3, Zayo, CenturyLink or XO Communications, Hemphill said.

In turn, the small telephone and cable companies help connect the major carriers to suburban or rural customers that they couldn't otherwise reach. The 511 Building is the largest of four carrier hotels in downtown Minneapolis when it comes to the number of fiber-optic cable connections to the outside world. Collectively, the four carriers may handle as much as half of the state's data traffic -- no one knows for sure. Another large chunk of Minnesota's data traffic is handled by private Internet connections owned by the telecommunications carriers or large corporations. It's not even clear how much data flows through the 511 Building, "given that Internet traffic does not flow exclusively through one data center," said Kharbanda.

But there are hints. In one corner of a 511 Building data center run by Cologix, several racks of computer gear can handle 50 million megabits per second -- about 5 million times faster than a home broadband connection. And that represents a tiny fraction of the building's data-moving capacity.

Kharbanda declined to say how many tenants the 511 Building has now.

Sometimes telecommunications firms will locate in more than one of the local carrier hotels to protect themselves against a failure at any one site.

"The 511 Building is certainly an economic engine in the digital economy," said James Farstad, a Minneapolis technology consultant. "But you don't want to put all your eggs in one basket."

For example, Internet services company ipHouse has its headquarters in the Tritech Building (a carrier hotel at 331 2nd Av. S.) but also has connections in the 511 Building. "We get connectivity to the outside world in both places," said Bil MacLeslie, ipHouse president.

Cost 'off the chart'

All of this suggests that the 511 Building is worth a lot of money and could have added substantially to the cost of the stadium if it had been torn down. Hemphill believes the cost of replacing the 511 Building -- including tearing up streets to relocate all those cables -- could have exceeded the projected $975 million cost of the new Vikings stadium.

"The cost is off the chart, just unreal," Hemphill said.

Farstad said the cost would have been high, but not that high. "It would be a significant expense to relocate a facility of that magnitude," he said.

Because tearing down the building never became an official part of the plan, the costs of doing so were never calculated, said Michele Kelm-Helgen, chairwoman of the Minnesota Sports Facilities Authority, to which the Legislature assigned the task of designing, constructing and operating the planned stadium. In the end, the site was extended in the opposite direction from the 511 Building, she said.

But while the 511 Building was spared, some tenants are not happy that the Vikings took away the facility's relative anonymity. Hemphill said security is a big issue because the building's Internet connections are considered vital infrastructure, and because some government agencies rely on its computing and data backup facilities.

"The building has awesome security," he said. "But some tenants worry about terrorism."

Steve Alexander • 612-673-4553