There are a bunch of different 802.11 Wi-Fi standards, e.g. 802.11a, 802.11b, 802.11g, 802.11n etc. that all support different speeds. Wi-Fi frames are generally categorised as one of the following:
- Data frames - carry the actual application data
- Control frames - coordinate when its safe to send/reduce collisions
- Management frames - handle connection discovery/setup/tear down (e.g. AP discovery, association, disassociation)
My question is about whether all these frames, and specifically management frames, are transmitted at the fastest supported speed available, or whether certain classes of frames are transmitted at some lowest common denominator speed. I have noticed that when I put an 802.11b/g only device into monitor mode and capture traffic over the air, I still see management frames (e.g. association/disassociation) being transmitted between my phone and AP which are both 802.11n, even though 802.11n has a higher transfer rate. So I am imagining one of two possibilities:
- My 802.11n phone/AP had to negotiate a slower speed for some reason and that's why I can see their frames on my 802.11b/g monitoring device.
- Management frames (and perhaps control frames also?) are sent at a lower speed, and it's only data frames that are transmitted faster with newer 802.11 standards.
The reason I would like to know which one of these two possibilities (or perhaps a third possibility) is the case is that I want to capture management frames, and need to know whether using an 802.11b/g card is going to lead to me missing some frames sent at higher speeds than the monitoring card can observe. If management frames are indeed sent at a slower rate, then it's all good. If I just happen to be seeing the management frames because my phone/AP have negotiated a slower rate though, then I need to reconsider what card I use for packet capture.