Could AP and station transmit at different physical data rates?
For instance we have 802.11b AP and station. I set fixed data rate for AP 5.5 Mbit/s, for station 11 Mbit/s.
AP announce about supported date in Beacon frame.
Also information about supported data rates is carried in Association Request and Association Response frames.
Additionally each 802.11 frame rate information is carried in PLCP header.
Let go back to my example and association process.
I suppose there are two scenario.
First. Association will fail, because there is no common supported rate. Such answer I get from instructor, when I have attended first level CWNA course.
Second. Association will finish successfully. AP will sent data at rate 11 Mbit/s (because station announce this supported data rate), and station at rate 5.5 Mbit/s.
What scenario is correct? It is vendor dependent or strictly defined in 802.11 standards?
If the AP is requiring (basic) a certain data rate and the STA doesn't support it, then it will not associate. The decision is made by the AP, not the STA.
I usually have long drawn out answers.. but hopefully that answers your question. Let us know if that works for you!