SFD

PHY 16 bits HR/DSSS long preamble PPDU unverified

Start frame delimiter — a fixed 16-bit pattern marking the end of synchronisation and the start of the header.

Where it sits

HR/DSSS PPDU (long preamble) > SFD

Accuracy

Clause
802.11-2024 §16.2.2.2
Verified
Not verified against the standard. Treat this as a claim, not a fact.