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In the IEEE 802.11 wireless LAN protocols (such as Wi-Fi), a MAC frame is constructed of common fields (which are present in all types of frames) and specific fields (present in certain cases, depending on the type and subtype specified in the first octet of the frame).

The very first two octets transmitted by a station are the Frame Control. The first three subfields within the frame control and the last field (FCS) 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 four bits Subtype subfield.

Frame control

The first three fields (Protocol Version, Type and Subtype) in the Frame Control field are always present. The fields, in their order of 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 two-bit protocol version subfield is set to 0 for WLAN (PV0) and 1 for IEEE 802.11ah (PV1). The revision level is incremented only when there is a fundamental incompatibility between two versions of the standard. PV1 description is incorporated in the latest 802.11-2020 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.

Protected frame

Set to 1 if the Management Frame is protected by encryption as described in IEEE_802.11w-2009.

+HTC/order

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

• It is set to 1 in a non-QoS data frame transmitted by a non-QoS WLAN station to indicate the frame being transmitted is using Strictly-Ordered service class (this use is obsolete and will be removed from the future 802.11 Standard).
• It is set to 1 in a QoS data or management frame transmitting at HT or higher rate to indicate that the frame contains HT Control field (see above)

References

1. "802.11 frames : A starter guide to learn wireless sniffer traces". community.cisco.com. October 25, 2010. Retrieved February 20, 2019.
2. 802.11 Working Group. "Part 11: Wireless LAN Medium Access Control (MAC) and Physical Layer (PHY) Specifications". 2016. New York, NY: IEEE: 638. {{cite journal}}: Cite journal requires |journal= (help)CS1 maint: numeric names: authors list (link)
3. LAN/MAN Standards Committee (February 9, 2021). IEEE Standard for Information Technology--Telecommunications and Information Exchange between Systems Local and Metropolitan Area Networks--Specific Requirements Part 11: Wireless LAN Medium Access Control (MAC) and Physical Layer (PHY) Specifications Amendment 1: Enhancements for High-Efficiency WLAN. New York, NY: IEEE Standards Association. p. 76. doi:10.1109/IEEESTD.2021.9442429. ISBN 978-1-5044-7390-3.
4. ^ Rapp, Dale (May 17, 2014). "THE TO DS AND FROM DS FIELDS". DALESWIFISEC. Retrieved August 13, 2019.

• Wi-Fi
• Networking standards