Wi-Fi 6 in Wireshark

The IEEE 802.11ax High Efficiency (Wi-Fi 6) amendment is currently being finalized by the IEEE. Many of  the exciting features like OFDMA Resource Units (RUs) and uplink and downlink MIMO are not configurable in the wireless controller. Therefore one of the best ways to determine what your Wi-Fi 6 APs and client supports is to take an over-the-air packet capture and look at beacons and association requests packets.

I have talked about how to do this in previous blogs, so in this blog I want to focus on some other Wi-Fi 6 goodness that you can see in Wireshark. In this blog, we will explore how RU and uplink and downlink spatial streams are allocated to users.

Wi-Fi 6 Trigger Frames and Resource Units

The 802.11 specification includes multiple trigger frames types. These trigger frames have the same format. You can see this format and a description of the fields in the 802.11 specifications, as shown below.

The common info, as the name implies, carries information that is the same (common) for all responding stations, such as instructions that tell the clients when to start and stop their transmissions. The user info contains information that is for a specific client. For example, if the AP is allocating resources to multiple clients, then there would be one user info for each client that the AP is allocating resources to.

The AP uses the “basic” trigger frame to allocate ODMA Resource Units (RUs) and spatial streams to clients that the respective clients can then use to transmit. The packet capture below shows a basic trigger frame, and the user info for two clients has been expanded.

 
You can see that the first client with AID 1 has been allocated RU allocation 53, which is 106 OFDMA tones and 2 spatial streams. The second client has been allocated RU allocation 39, which is 52 tones, and also 2 spatial streams.

The RU allocation indicates both the RU size and where it is in the operating channel. The picture below shows the RUs that were allocated in this specific basic trigger frame. 

You may be wondering how I knew it was a 20 MHz channel and not a 40 or 80 MHz channel. That information is common to all the clients, and therefore that is in the common info. See the expanded pcap below.

I hope you found this blog useful. Keep in mind you can refer to the 802.11 specifications for details on the frame format and additional information on the fields you find in your pcaps.