In a method for generating a data unit, it is determined whether the data unit is to be transmitted using single carrier (SC) modulation or orthogonal frequency division (OFDM) modulation. When it is determined that the data unit is to be transmitted using SC modulation, a header field of the data unit is generated using a first technique to indicate that the data unit conforms to a first protocol and/or whether the data unit conforms to a first PHY mode or a second PHY mode of the first protocol. When it is determined that the data unit is to be transmitted using OFDM modulation, the header field is generated using a second technique to indicate that the data unit conforms to the first protocol and/or whether the data unit conforms to the first PHY mode or the second PHY mode of the first protocol.