Sunday, July 8, 2012

802.11 Frame types

802.11 Frames are devided into three categories.

1. Managment Frames
2. Control frames.
3. Data Frames

1. Management Frames
  •    Managment Frames are used by Wireless stations to join and Leave the Basic Service Set
  •    Another name for Managment Frames is "MAC protocol Data Unit"(MMPDU)
  •    There is no MSDU encapsulated in the MMPDU frame body , which carries only layer2 information fileds and information elements
   Following are the list of all 12 of the Managment frame subtypes as defined by 802.11 standard

    Assosiation Request
    Assosiation Response
    Reassosiation Request
    Reassosiation Response
    Probe request
    Probe Response
    Announcement Traffic Indication Message(ATIM)

2. Control Frames
  •     802.11 Control frames assit with the delivery of the data frames. 
  •     Control frames must be heard by all the stations, therefore they must be transmitted at one of the basic rates
  •     Control frames are also used to clear the channel,acquire the channel and provide the unicast frame acknowledgements
  •     They contain only header information
    Following are the list of control frame subtypes as defined by 802.11 standard

    Power Save(PS) Poll
    Request to Send (RTS)
    Clear to send (CTS)
    Contention-Free(CF)-End (PCF only)
    CF-End+CF-ACK (PCF only)
    Black Ack Request(HCF)

3.Data Frames
  •    Most of the Data Frames carry actual data that is passed down from higher layer protocols
  •    Some 802.11 data frames contain no data at all but do have a specfific purpose within BSS
  •    There are 15 data frame subtypes 
Data+CF-Ack (PCF only)
Data+CF-Poll (PCF only)
Data+CF-Ack+CF-Poll (PCF only)
Null data (no data transmitted)
CF-Ack (no data transmitted) (PCF only)
CF-Poll (no data transmitted) (PCF only)
Data+CF-Ack+CF-Poll (PCF only)
Qos Data (HCF)
Qos Null (No Data) (HCF)
Qos Data+CF-Ack (HCF)
 Qos Data+CF-Poll (HCF)
 Qos Data+CF-Ack+CF-Poll (HCF)
Qos Cf-Poll(HCF)
Qos CF-ACK+CF-Poll (HCF)

See some of below combination for different frame types.


  1. May I know , what is the PCF or HCD mentioned in types of Data Frames ?

    1. PCF mean Point coordination Function. and HCF mean Hybrid coordination Function.

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  3. Thank you , it's a detailed and objetive information about data frames in 802.11 =D

  4. I found a typo in "2. Control Frames": "802.11 Control frames assit with the delivery of the data frames."
    assit -> assist

    Thank you so much for your information.

    1. Also I a recurring error: assosiation needs to be association.
      s -> c

  5. Which one of these frames could i use to identify the clients of an Access Point. I do understand that beacon frames are there to make stations know about the presence of a wireless network but how stations make other stations and AP's know about their presence.

    1. Get in to the control frame display filter my applying AP's MAC its displayes conencted clients under it

  6. Hi NagaBabu,

    Can you please explain why we need PCF,DCF,HCF in CSMA/CA ?