802.11 Frame Types


In the IEEE 802.11 wireless LAN protocols, a MAC frame is constructed of common fields and specific fields.
The very first two octets transmitted by a station is the Frame Control. The first three subfields within the frame control and the last field are always present in all types of 802.11 frames. These three subfields consist of two bits Protocol Version subfield, two bits Type subfield, and two bits Subtype subfield. The remaining subfields can be present or absent depending on the setting of the Type and Subtype subfields.

Frame Control

The first three fields in the Frame Control field are always present. The fields in the order appearance in transmission are:
  1. Protocol Version
  2. Type
  3. Subtype
  4. To-DS
  5. From-DS
  6. More-Fragments
  7. Retry
  8. Power Management
  9. More Data
  10. Protected Frame
  11. +HTC/Order

    Protocol Version Subfield

The 2-bits Protocol Version subfield is currently always set to 0, regardless of 802.11 version being used. The revision level is incremented only when there is a fundamental incompatibility between two versions of WLAN standard.

Types and SubTypes

ToDs and FromDS

ToDS is one bit in length and set to 1 if destined to Distribution System), while FromDS is a one-bit length that is set to 1 if originated from Distribution System).

Retry

Set to 1 if the Data or Management frame is part retransmission of the earlier frame. This bit is reused for different purpose in Control frame.

+HTC/Order

It is one bit in length and is used for two purposes: