Wi-Fi devices from Apple unable to connect to an 802.11n Wi-Fi network
This applies only to third-party routers. Apple AirPort products do not have a setting to enable or disable WMM.
WMM must be enabled for devices to connect. Disabling WMM on your wireless router can prevent the following Apple products, iPad, iPhone, iPod touch and Apple TV, from connecting to an 802.11n Wi-Fi network.