A complete MAC frame: header, body, and frame check sequence.
Reading a capture
Everything the MAC adds is overhead on top of the data someone actually wanted to send. At 26 octets of header plus 4 of FCS, a frame carrying a 64-octet payload spends a third of its airtime on framing.
Subfields
Frame Control — Identifies what kind of frame this is and carries the flags that change how the rest of the header is read.
Duration/ID — Usually the time in microseconds that other stations should treat the medium as busy. In some control frames it carries an association identifier instead.
Address 1 — Receiver — The receiver address: the station this frame is being transmitted to over the air right now.
Address 2 — Transmitter — The transmitter address — the station physically sending this frame.
Address 3 — The address whose meaning depends entirely on To DS and From DS — the original source, the final destination, or the BSSID.
Sequence Control — Identifies this frame within a sequence, and its fragment position.
Address 4 — The original sender, in a frame travelling between two access points.
QoS Control — Present only in QoS subtypes. Carries the traffic class and how this frame should be acknowledged.
Frame Check Sequence — A 32-bit cyclic redundancy check over the header and body.