802.11 Frame Types

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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 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 is 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 two bits Subtype subfield. The remaining subfields can be present or absent depending on the setting of the Type and Subtype subfields.

Frame Control[edit]

802.11 Frame Control Field

The first three fields (Protocol Version, Type and Subtype) in the Frame Control field are always present. The fields in the order appearance in transmission are:

  1. Protocol Version (currently is 0)
  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[edit]

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.[1][2]

Types and SubTypes[edit]

Various 802.11 Frame Types and Subtypes
Type Value

B3..B2

Type

Description

Subtype Value

B7 .. b4

Subtype Description
00 Management 0000 Association Request
00 Management 0001 Association Response
00 Management 0010 Reassociation Request
00 Management 0011 Reassociation Response
00 Management 0100 Probe Request
00 Management 0101 Probe Response
00 Management 0110 Timing Advertisement
00 Management 0111 Reserved
00 Management 1000 Beacon
00 Management 1001 ATIM
00 Management 1010 Disassociation
00 Management 1011 Authentication
00 Management 1100 Deauthentication
00 Management 1101 Action
00 Management 1110 Action No Ack (NACK)
00 Management 1111 Reserved
01 Control 0000-0001 Reserved
01 Control 0010 Trigger
01 Control 0100 Beamforming Report Poll
01 Control 0101 VHT/HE NDP Announcement
01 Control 0110 Control Frame Extension
01 Control 0111 Control Wrapper
01 Control 1000 Block Ack Request (BAR)
01 Control 1001 Block Ack (BA)
01 Control 1010 PS-Poll
01 Control 1011 RTS
01 Control 1100 CTS
01 Control 1101 ACK
01 Control 1110 CF-End
01 Control 1111 CF-End + CF-ACK
10 Data 0000 Data
10 Data 0001 Data + CF-ACK
10 Data 0010 Data + CF-Poll
10 Data 0011 Data + CF-ACK + CF-Poll
10 Data 0100 Null (no data)
10 Data 0101 CF-ACK (no data)
10 Data 0110 CF-Poll (no data)
10 Data 0111 CF-ACK + CF-Poll (no data)
10 Data 1000 QoS Data
10 Data 1001 QoS Data + CF-ACK
10 Data 1010 QoS Data + CF-Poll
10 Data 1011 QoS Data + CF-ACK + CF-Poll
10 Data 1100 QoS Null (no data)
10 Data 1101 Reserved
10 Data 1110 QoS CF-Poll (no data)
10 Data 1111 QoS CF-ACK + CF-Poll (no data)
11 Extension 0000 DMG Beacon
11 Extension 0001-1111 Reserved


ToDs and FromDS[edit]

ToDS is one bit in length and set to 1 if destined to Distribution System)[3], while FromDS is a one-bit length that is set to 1 if originated from Distribution System)[3].

Retry[edit]

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[edit]

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[edit]

  1. ^ "802.11 frames : A starter guide to learn wireless sniffer traces". community.cisco.com. 2010-10-25. Retrieved 2019-02-20.
  2. ^ 802.11 Working Group. "Part 11: Wireless LAN Medium Access Control (MAC) and Physical Layer (PHY) Specifications". 2016. 3 Park Avenue, New York, NY 10016-5997, USA: IEEE: 638.
  3. ^ a b Rapp, Dale. "THE TO DS AND FROM DS FIELDS". DALESWIFISEC. Retrieved 13 August 2019.