So you just received your brand new 802.11ac USB adapter, capable of 867 mbps, and you plug it in and run a diagnostic program and wait, what’s this? It says it is a USB 2.0 device? You run another diagnostic program and it says the same thing! You know that USB 2.0 is only capable of 480 mbps. So the adapter is not really 867 capable after all….hmmmmm...but wait, actually it is.
The reason this happens is because the driver switches between USB 2 and USB 3 modes as needed.
These devices are backward compatible with older networks that have speeds below 480 mbps, such as 802.11n 150 and 300 mbps networks. The default mode of these USB 3.0 devices according to diagnostics is USB 2.0. When you are not connected to any network, this is the mode that will be displayed. When you connect to an 802.11n network, or a 1T1R 802.11ac network, the adapter will stay in USB 2.0 mode because the max speed of 480 for USB 2.0 is more than your network connection rate.
But connect to an 802.11ac network above 480, such as an 867 mbps 802.11ac 5 GHz network, and then check diagnostics again. Now it shows USB 3.0 as the mode. The chipset uses smart switching to go into either mode depending on what type of network to which you are connected.
Understanding mode switching in Realtek RTL8812AU 802.11ac Windows drivers
posted 2016 Feb 23 by