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802.11 Medium Contention


Wireless is a half-duplex medium. Unlike Ethernet, wireless devices must contend for air time to transmit their frames. To avoid collisions, there are a number of mechanisms used:

  • Physical Carrier Sense
  • Virtual Carrier Sense
  • a Coordination Function

In this episode, I go over these mechanisms and describe their purpose.

Here is a screenshot of a wireless frame showing the Duration value within the header. This Duration value is used to set a device’s NAV timer.


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Rowell, CWNE #210, is a network engineer in Higher-Ed. He enjoys working with wireless networking technologies and loves to share and engage with the community. You can connect with him on Twitter, LinkedIn, and Facebook.

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