I'm new to Wireshark. I'd like to know what are fixed and tagged parameters and the difference between them. Web search didn't help. Kindly explain it to me in simple terms.
I don't believe that is a thing in wireshark. However, there are a pair of fields in wireshark's decode output for the 802.11 protocol with these names. In that context, fixed parameters are those which exist for all frames (at specified offsets), and tagged parameters are variable. They exist in the tagged parameters area, and include a tag (to show which parameter is being specified) and some paramater-specific data. There might be several of them. Other than the details of how they are encoded and whether they appear in all packets, the distinction is not very meaningful.
This technique is used in other protocols too (with different names). For instance, DHCP options are encoded in a similar fashion.