Inside the huge data centers operated by Internet companies like Google, Amazon, and Facebook, information is processed at blistering speed, but it still has to be moved between different machines through relatively slow wiring.
In theory, this bottleneck could be avoided by adding wired links between racks, but that would be very expensive and, short of a complete architectural redesign, not particularly practical. Transmitting data wirelessly would be simpler, but achieving the required speed would normally require a line-of-sight connection, which is impossible in a packed data center.
Researchers from the University of California, Santa Barbara, and Intel’s labs in Oregon have come up with a clever solution: bouncing wireless signals off the ceiling, which they say could boost data transmission speeds by 30 percent.
Congestion caused by short bursts of activity inside data centers is a growing problem, says Heather Zheng, an associate professor of computer science at the University of California, Santa Barbara, who led the work.
Zheng and colleagues used 60-gigahertz Wi-Fi, which has a bandwidth in the gigabits-per-second range and was developed for high-definition wireless communications (the first commercial products that use the standard will hit the market next year). However, it has its limitations, says Zheng. To maximize the bandwidth and reduce interference between signals, it needs to be focused into narrow beams that require a direct line of sight between endpoints. “Any obstacle larger than 2.5 millimeters can block the signal,” she says.
One way to prevent the antennas from blocking each other would be to allow them to communicate only with their immediate neighbors, creating a type of mesh network. But that would further complicate efforts to route the data to the appropriate destinations, says Zheng. Bouncing the beams off the ceiling directly to their targets not only ensures direct point-to-point communication between antennas but also reduces the chances that any two beams will cross and cause interference. “That’s very important when you have a high density of signals,” she says.
Flat metal plates placed on the ceiling can provide nearly perfect reflection. “You also need an absorber material on the rack to make sure the signal doesn’t bounce back up,” says Zheng.
Working with colleagues at UCSB along with Lei Yang from Intel Labs in Oregon and Weile Zhang at Jiao Tong University in Xi’an, China, Zheng created a simulation of a 160-rack data center to see how the system might affect performance. “Our simulation shows that wireless can add 0.5 terabytes per second,” she says.
IBM is also looking into using wireless technology in data centers, says Scott Reynolds, a researcher at IBM’s T.J. Watson Research Center in Yorktown Heights, New York, who has been developing 60-gigahertz systems. “These data centers are just choked with cables,” he says. “And so every time you want to reconfigure one it’s very labor intensive and expensive.” But one problem with turning to wireless transmission, he adds, is that “you need to have hundreds of these wireless data links operating in a data center to be useful.” Since 60-gigahertz Wi-Fi has only four data channels, it’s important to configure the beams so they don’t interfere with each other.
Zheng and her colleagues are now working on building a prototype data center to put their solution into practice.