Last Post: September 29, 2006:
My impression is that the 12-bit sequence number field has nothing to to with 802.11 security issues such as preventing spoofing. It is strictly a fragmentation and inadvertant duplicate frame discovery mechanism.
Both 802.11 Robust Security Network (RSN) cipher suites, TKIP and CCMP, have 48-bit sequence counters used for confidentiality and integrity of encrypted frames. This includes protection from advertant duplication of frames.
I hope this helps. Thanks. /criss