The Physical Protocol Data Unit
(PPDU) is the protocol data unit (PDU) ofthe physical layer
. In WLANs according to 802.11, the protocol header contains the effective length of the data packet. In WLAN systems with a low transmission speed of 1 Mbit/s, the PPDU length is 192 µs; in faster WLAN systems it is only half as long at 96 µs. A PPDU begins with the 12-symbol PLCP preamble, Physical Layer Convergence Protocol (PLCP), which consists of a synchronization field (SYNC) and a start frame delimiter (SFD).