How Does AT&T Detect Unofficial iPhone Tethering?

BY Jason

Published 9 May 2011

iPhone Tethering

As we’ve reported earlier, AT&T continues to clamp down on unofficial iPhone tethering, which is one of the main reasons users jailbreak their iPhone.

There has been a lot of debate and speculation on how AT&T detects the unofficial iPhone tethering. Android Police has provided some insight into how AT&T is able to identify users who are using the unofficial tethering option.

Android Police explains:

Jailbroken iPhones typically use the same tethering technique as a standard iPhone, the one that’s already present in iOS. This method exposes tethering activity quite readily, because the iPhone, when in tethering mode, sends traffic through an alternate APN (AT&T access point/router) for the express purpose of identifying the traffic as tethered data. This makes it extremely easy for AT&T to identify whether or not an iOS device is utilizing tethering, and just how much of their data is consumed via tethering.

Some tethering applications for iOS make use of alternative methods and route tethered traffic through the phone’s normal data APN, but by and large, most jailbreakers stick with the stock application because it’s easy to use and doesn’t require any complicated setup. In fact, many iPhone users jailbreak for the sole purpose of avoiding AT&T’s tethering fees (for why, see next section). These are the people AT&T’s is going after.

According to Android Police, popular jailbreak apps such as MyWi and Tetherme use the tethering APN instead of using the normal data APN.

It’s not clear if PdaNet that has been updated recently to hide unofficial tethering by masking the packets uses iPhone’s normal data APN to go undetected (assuming it does). If PdaNet’s solution works then we’re quite sure that other developers will soon release an updated version of their jailbreak apps to stay ahead of the cat and mouse game with AT&T.

It is unfortunate that carriers are charging users for the tethering option or don’t allow some features or apps to work to use iPhone’s 3G data connection (work only over Wi-Fi). Ideally, we should be able to use the data the way we want as we’ve paid for it.

What do you think?