The following shows the association, authentication and data traffic of a 11ac 3SS client using a 802.11ac and 802.11n sniffer. The main idea of this exercise is to show that the 802.11n sniffer will not be able to interpret and capture any 802.11ac encoded frames (mainly unicast QoS data frames).
The capture on the left is the 802.11n capture and the one on the right is the 802.11ac capture. As you see all management and controller frames can be seen on both captures as they are sent using legacy rates to maintain backward compatibility in a mixed mode environment.
Now in the above capture you see that the EAPOL keys 3 and 4 are still visible on both captures but the QoS data frames (priority 6 - TID 6) are only seen on the capture on the right (802.11ac capture). You can see some of the VHT information in the VHT information field of the QoS data like — 80 MHz channel is used, the STA is a 3 spatial stream (3 SS) STA, and MCS 8 (256 QAM 3/4).
The 802.11n sniffing device cannot interpret these 11ac data frames.
