Thursday, December 1, 2016

Understanding QoS Control IE: Contains 802.11e Standard's Features

In this post, we will decode the QoS control IE. As QoS was introduced in 802.11e, this IE is loaded with the functionalities introduced in 802.11e. A quick recap of what was introduced in 802.11e:

  • QoS: Defines 8 priority levels (lower 4 priorities used for EDCA) . Hence, traffic needs to carry this information.
  • UAPSD: Lead to introduction of End-of-Service-Period (EOSP) field. 
  • Block ACK: Lead to introduction of ACK policy field which can take one of the four values:
    • Normal ACK or Implicit BAR
    • No ACK
    • No Explicit Acknowledgement or Scheduled Ack under PSMP
    • Block ACK
  • TXOP / Queue Size related fields
QoS Control field is available in QoS data packets i.e. data packets of QoS subtype. As we can see below, there are 15 type of data frames (source).  Frame exchanges b/w QoS stations will be QoS data frames whereas b/w legacy devices or b/w QoS & legacy device will be non-QoS frames.

Features introduced by 802.11h:
  • DFS
  • UNII-2e band
  • Action frames

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