Visualizing 802.11 Frame Formats

 The IEEE 802.11 defines frame formats that are used within the MAC layer of the protocol stack. Looking up frame formats in the standard is useful to understand how these frames are structured. In this post we are going to use the 802.11-2016 standard which, at the time of this writing, is available for free using the IEEE GET Program.

Open the 802.11 standard pdf document, and search for “frame format”.


There is a tremendous amount of great information on these sections of the standard. For this example, we will be looking at section “9.3.1.1 Format of Control frames”. More specifically, let’s take a look at the difference between an RTS and CTS frame’s format. 

We can see the RTS frame is made of 20 octets, vs the CTS frame which is made of 14 octets. The RTS frame requires the Receiver Address (RA) to identify the station the this frame is being sent to, and it also needs the Transmitter Address to identify the station transmitting the frame, so the receiver knows which station to respond to. However, the CTS frame only needs the RA, because when the receiving station receives the CTS response it knows which station it is from. That is, the station receiving the CTS knows who it sent the RTS too.

This is only a basic example of how we can leverage this section of the standards. Seeing the structure and contents of frames in this way is useful in understanding how the protocol works. Looking at common frame types, like the example above, also reinforces and helps to visualize the way in which these frames are different.

The 802.11 specifications may be thousands of pages long and seem quite overwhelming. But they can be invaluable as a reference for looking up frame formats and field definitions.

I encourage you to go to browse the standards on this IEEE webpage and expand "IEEE 802.11: Wireless LANs" to download the 802.11 specifications that interest you.

As always, I hope you found this blog helpful.