Strange Xbox signal suspected of jamming wireless LANs

It's not clear whether the signal disrupts a US college's WLAN access points or students' wireless notebooks, but it at least affects other radios in the same 2.4GHz band.

Microsoft's popular Xbox 360 game console can create a strong and strange signal on wireless LANs, according to IT staff at Morrisville State College.

It's not clear whether the signal disrupts the college's WLAN access points or students' wireless notebooks. There is some anecdotal evidence, however, that it at least affects other radios in the same 2.4GHz band.

Morrisville IT staff typically use Bluetooth headsets, which run in the 2.4GHz band, with their mobile phones when they troubleshoot problems on the spacious campus. "We had problems syncing our headsets to our phone where this signal was strong," says Matt Barber, the college's network administrator. A phone user had to physically touch the headset to the cell phone to make the initial connection, he says.

There may be effects on the WLAN that the equipment itself, from Meru Networks, is circumventing, according to Barber. Part of Meru's WLAN architecture employs software that gives the access points more control over wireless-client transmission behavior than does the software of some of Meru's rivals. An access point near a radiating Xbox may be compensating for interference by in effect guiding a wireless laptop to send and receive when open spectrum is available, essentially dodging around the Xbox signal.

Working with Meru, the small IT staff is planning to test soon the effect of multiple Xbox consoles in a dorm with a large number of active notebook clients.

Network World has asked Microsoft to comment on the Xbox signal phenomenon, but the company was not able to reply before this story was posted. We'll update this report as soon Microsoft provides information.

The latest version of the Xbox, the Xbox 360 Elite, went on sale earlier this year with a 120G-byte hard disk and a high-definition video interface.

Morrisville is a small college in rural New York state, taking its name from a nearby town. In summer 2007, the college deployed a campuswide 802.11a/b/g WLAN based on equipment from Meru.. The plan was to replace those access points with Meru's new, two-radio devices that added support for Draft 2 of 802.11n, the IEEE standard that boosts throughput from 22M to 25Mbps to at least 150M to180Mbps. That replacement was just completed, creating the first large-scale deployment.

During the fall, Morrisville IT staff, working with Meru engineers and IBM, the network integrator, detected an unusual signal in the 2.4GHz band. "We wanted to look at the [radio frequency] environment in our dorms," Barber says. "We always thought we'd run into some strange stuff [there] in the 2.4 range."

The signal was discovered using Cognio Spectrum Expert, from Cognio (recently bought by Cisco). Spectrum Expert is RF-analysis software packaged with a WLAN adapter card that slots into any laptop PC. Among other capabilities, Spectrum Expert identifies sources of radio energy in the 2.4GHz and 5GHz WLAN bands, and identifies the cause, such as a brand of access point or a microwave oven.

"The signal really stood out," Barber says. "In some places it was so strong we thought it might be affecting the air [that is, the radio environment] around it."

The Cognio software, however, was baffled by this new signal: "Unknown emitter" was the classification. The signal shows up in the Cognio display as a kind of green-blizzard effect, covering a large swath of the 2.4 band, Barber says. That means the signal "is jumping all over the spectrum band," he says. In contrast, a nearby Meru access point shows up in the same scan as a strong, stable yellow-red glow, almost like a sun. The green blizzard is shot through with red dashes, which show, Barber says, that the signal at moments nearly rivals the access point in strength.

The mystery signal baffled the IT staff and Meru until Barber had a brainstorm: He brought in his own Xbox 360 and plugged it in, and turned on the Cognio spectrum analyzer. Presto: The same signal appeared.

Barber says the signal seems be created by the console's embedded 2.4GHz radio, which is used to communicate with the handheld wireless controller -- the gizmo with the buttons that manipulate a game running on the console. The Xbox also takes an optional Wi-Fi adapter, in the form of an USB dongle, to connect to a WLAN access point.

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John Cox

Network World

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