preamble (802.3) (PA)
The preamble(PA) is the first data field in various protocols. The preamble is used to synchronize the stations to the clock rate of the frame. Preambles are used, for example, in Ethernet and Z-Wave.
With the classic Ethernet, which works with Manchester coding, the preamble is a square wave of 10 MHz. Depending on the Ethernet version, the preamble is of different length. In the version according to the DIX standard (DIX V2.0) it has a length of eight octets, according to IEEE 802.3 it is seven octets long.
The preamble consists of a 1-0 bit combination 10101010, which is repeated seven times. In Ethernet, the preamble is followed by the start frame delimiter( SFD) with the bit combination 10101011. These bit sequences specify the clock rate, facilitate collision detection and clearly define the start of the data packet.