Preamble (32 bits)
Used for synchronization
SFD (8 bits)
A fixed pattern of bits that indicates the end of the preamble and the start of the data
Frame length (8 bits)
The first 7 bits indicated the length of the payload
The additional reserved bit makes one octet long
Payload (variable)
Either five octets long (containing an ACK) or 8 to 127 octet long
Frame lengths of zero to four, six or seven octets are reserved by the standard