The broad class of frame.
Two bits, and the first structural decision in the frame. They decide whether there is a Frame Body at all, whether the header is three addresses or four, and how everything after Address 3 is read — so nothing further in the frame can be parsed until these are. Read on its own it still says almost nothing: Type tells you which of four registries the Subtype belongs to, and the same four Subtype bits mean entirely different frames in each. Extension exists because those four bits ran out.
| Value | Meaning |
|---|---|
| 00 | Management — establishes and maintains the BSS. Carries no user data, and is sent in the clear until a key exists. |
| 01 | Control — clears the medium and acknowledges. The shortest frames on the air, and the only ones with no frame body. |
| 10 | Data — the only type that carries anything the user sent. |
| 11 | Extension — added when the four Subtype bits ran out; the Subtype field then names a whole new frame format. |
Bit values written b0 first, matching transmission order.
QoS Data MPDU > Frame Control > Type