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What is flexible client access (FCA) and when and where can it be use effectively?

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TitleWhat is flexible client access (FCA) and when and where can it be use effectively?
Question
What is flexible client access (FCA) and when and where can it be use effectively?
Environment
  • identiFi wireless
  • Flexible client access (FCA)

 
Answer
What is the use case for FCA:
  • 802.11 MAC layer shares the medium based upon packets not the airtime that is use to transmit them
  • Slower (legacy) clients take a proportionally larger amount of air time than a modern fast client, the net result being the medium is not use in an optimum way.
How is it implemented and where FCA will help or not help

AP37xx/AP38xx AP hardware
  • AP solutions developed during the 802.11n era, typical deployments were mixed 802.11b/g clients and 802.11g/n clients.
  • Low end or legacy clients may not support 5Ghz
  • Uses a RED (Random Early Detect) rate limiter that drops packets proportional to the client PHY rate, the higher the data rate, the lower the drop.  This rate is tracked across all clients, not per client
  • Use case: Where there is a high percentage mixed client types 11 b/g/a and 11n/ac
  • What it doesn't do: FCA will not help with congestion especially when the client types are all the same.
AP39xx AP hardware
  • Developed in an era where most clients are 11n or 11ac capable.
  • Use FCA to share the medium between different WLAN's
  • Uses an air time based token bucket and a scheduler to share the time when there is congestion based upon the configured air time
  • Use case: When you wish to give one WLAN more priority over another, for example a guest wlan might have less airtime than the production wireless wlan.
  • What it doesn't do: FCA will not help with congestion especially when the client types are all the same.
Additional notes
A general guideline is that FCA should only be used where it is believed that legacy clients are affecting 802.11n or 802.11ac throughput

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