Wednesday, June 9, 2010

Five Hundred Wi-Fi Networks Walk into a Bar

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By Glenn Fleishman

Steve Jobs is known for being cool but not necessary keeping his cool. At the company's announcement of the iPhone 4 at the Worldwide Developers Conference (WWDC), he looked a little steamed when demonstrations of the new phone's higher-density, more realistic display failed when he was unable to load Web pages over Wi-Fi. He asked reporters and conference attendees to turn off their gear to clear the radio frequency (RF) environment enough to make Wi-Fi work.

Was that a failure of the iPhone 4 to work over Wi-Fi, or a failure of Wi-Fi to be robust enough to handle a room of thousands of people? It might be what you think if you read much of the reporting about this network failure.

But that's not quite what happened. There wasn't one or two Wi-Fi networks running at the Moscone conference center, but several hundred, all beating each other up. According to InfoWorld's consultation with an Apple engineer at the event, over 500 networks were in operation at the same time.

How was this possible? Because so many people—likely a huge percentage of press attendees—were carrying cellular routers, like the MiFi. The MiFi picks up a 3G data signal and relies it over Wi-Fi, acting just like a Wi-Fi router. Some people were instead using a 3G modem plugging into a laptop, and using an easily accessible Mac OS X (or, gasp, Windows) feature to share the 3G connection via the laptop's Wi-Fi card.

There are Wi-Fi networks that have tens of thousands of simultaneous users spread over thousands of routers over a corporate or academic campus. Wi-Fi can handle that. And there are plenty of events at which the host creates a temporary Wi-Fi network with many interconnected routers that can handle hundreds to thousands of devices at once. The Macworld Expo is a notable case: the last time I attended, thousands of iPhones and laptops worked just fine over a unified, well-managed Wi-Fi network that spanned the conference area.

Apple apparently did offer a public Wi-Fi network at the WWDC launch, according to media and attendees I've polled. And those who tried it said that network did work initially. But with so much media in the audience, and the history of conference/event Wi-Fi networks having glitches at peak times—with many people liveblogging and uploading photos from the event—those who had MiFis chose to use those instead.

Wi-Fi can cope with a lot of so-called interference, but the protocol wasn't designed to handle hundreds of overlapping networks in a small space.

http://futuretense.publicradio.org/blog/index.php?id=677444556

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