A miniport can choose to run fully serialized or full-duplex unless it reports its medium type as NdisMediumWan. A WAN miniport driver always runs fully serialized.
If a miniport runs in full-duplex mode, it can send and receive simultaneously (assuming it is running in an SMP machine). If it does not run in full-duplex mode, the miniport is assured that sends and receives are serialized by NDIS.
A miniport that runs full-duplex indicates its support of this option when MiniportQueryInformation is called with the OID_GEN_MAC_OPTIONS request. Then, it sets the NDIS_MAC_OPTION_FULL_DUPLEX flag.