Efficient transmission for low data rate wlan

A network interface device utilizes a physical layer (PHY) protocol data unit (PPDU) maximum duration such that, (A) when operating in a first mode of operation, a data unit (i) defined by a protocol in a layer above a PHY protocol in a protocol stack and (ii) having a maximum length defined by the protocol above the PHY protocol will fit entirely within a single PPDU at a lowest possible data rate in the first mode of operation, and (B) when operating in a second mode of operation, the data unit (i) defined by the protocol in the layer above the PHY protocol and (ii) having the maximum length defined by the protocol above the PHY protocol will not fit entirely within a single PPDU at a lowest possible data rate in the second mode of operation.