BSS Coloring is a method to help counter co channel interference in wireless deployments. It was first introduced with 802.11ah, and is also featured in 802.11ax.
This technology works by adding a field to the frame header which essentially colors the frame. If a frame is heard on an AP´s channel, it is decoded, and the frame is checked to see if it has the same color as the access point. If it does, it´s considered an Intra-BSS Frame. The frame has a different color, and it is considered an Inter-BSS Frame.
Intra vs Inter-BSS Frames
An “Intra-BSS” Frame is a frame that is transmitted, intended for the specific access point, the access point has the same color assigned to it as the frame.
Inter-BSS Frame: Is a frame that is transmitted on the same channel, but not intended for the specific access point. The access point has a different color assigned to it compared to the frame.
Dealing with Inter-BSS Frames
The medium is considered busy while the frame is decoded and checked. Once it´s determined to be an Inter-BSS frame, and the received signal of the frame is under a threshold, the medium is considered clear. If the frame is above the threshold the medium is considered busy.