Facebook has a clever way to make sure its apps work on crummy Internet connections

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One of Facebook's Internet.org ads tells Neesha's story, a girl who has grown up with a family of magicians, but no internet.

But from Facebook's posh offices in Northern California, smack-dab in the center of Silicon Valley, it's easy to forget that not everybody has access to their kinds of high-speed, high-availability Internet connections.

Which is why at one of its latest world-famous hackathons, Facebook engineers built a system called the Augmented Traffic Control (ATC), a tool to help them figure out how their apps will work under the worst of network conditions and make them better for everybody, everywhere, whether or not they have access to 4G LTE or WiFi.

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"We specifically simulated the most common network connectivities in countries such as Brazil, India, Indonesia, Kenya, Nigeria, and the Philippines," writes the Facebook team in a blog post.

In practice, it lets Facebook engineers see how the app performs in low-connection areas. For instance, if you've ever tried to send a Facebook message from a subway tunnel, you may have noticed how the app gives up on trying to deliver the message after a few tries.

Facebook engineers work hard to optimize exactly long the app tries before giving up - in some countries, a signal may not be reliable enough the first time. The same principle goes for other stuff, too, like the maximum size of a picture file and the precise speed at which a slow connection makes an app unusable.

It's just stuff that's good to know if you want your app to be used by a broad range of people.

The inspiration for the ATC, writes the Facebook engineering team, came from a hacker convention in 2013 where some enterprising attendees used outdated phone hardware to make a totally private cellular network that only existed for as long as the event lasted.

So inspired, Facebook engineers decided to make private networks for testing that could be sped up or slowed down to test in a variety of conditions - the ATC.

The first step was building a private 2G data network that would let users make voice calls and send text messages, but it was hard for the Facebook team to find phones that would work with the cobbled-together network they were building.

Instead, the team built a software simulator into a WiFi network so that any Facebook engineer on the company's campus could purposely throttle their connection to pretend that they're accessing the network from 2G, Edge, 3G, and LTE networks.

The other cool part is that Facebook has released the ATC under open source as of today, which means anybody can use and build on its tools for measuring app performance under worse network conditions. It's another arrow in the quiver for those trying to get the rest of the world online.