In a mixed cell, all broadcast and multicast traffic sent by the access point is unencrypted. A client may attempt to join a mixed cell and use encryption for directed traffic by setting the privacy bit in the (re)associate request packet. If the cell supports encryption, a successful (re)associate response packet will be sent with the privacy bit set in the capabilities field. If the cell does not support encryption (it is not a mixed cell), then it will respond with a (re)associate response packet indicating a failure.
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Communications > 802.11 Radio > Funk Security > Profile # > Mixed Cell