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ONT Notes - QoS On Wireless Networks

  • Wireless LANs (WLANs)
    • Extensions to wired LANs
    • Carrier sense multiple access collision avoidance (CSMA/CA) as media access method
    • Uses distributed coordinated function (DCF) for collision avoidance
    • DCF is based on RF carrier sense, inter-frame spacing (IFS), and random wait timers
  • Wifi QoS standards
    • 802.11e
      • IEEE standard
      • 0-7 priority levels
    • Wifi Multimedia (WMM)
      • Four access categories
        • Platinum (voice) – 6 or 7 802.11e
        • Gold (video) – 4 or 5 802.11e
        • Silver (BE) – 0 or 3 802.11e
        • Bronze (Background) – 1 or 2 802.11e
    • WMM and 802.11e replace DCF with EDCF
  • Cisco Split-MAC
    • Splits functions between Lightweight access points (LWAPs) and WLAN controllers (WLCs)
    • LWAPs handle real-time functions
      • Beacon generation
      • Probe transmission and response
      • Power management
      • 802.11e/WMM scheduling and queuing
      • Packet buffering
      • Encryption/decryption
      • Control frame/message processing
    • WLCs handle non-real-time functions
      • Association/disassociation/reassociation
      • 802.11e/WMM resource reservation
      • 802.1x EAP
      • Key management
      • Authentication
      • Fragmentation
      • Ethernet-WLAN bridging
  • End-to-end QoS
    • Step 1:  WLC copies DSCP from switch to outer DSCP and outer 802.1p and sends to LWAP over LWAPP tunnel
    • Step 2:  LWAP copies outer DSCP from WLC to 802.11e/WMM field and sent to client
    • Step 3:  LWAP copies 802.11e/WMM value from the client to outer DSCP and sends it to WLC
    • Step 4:  WLC copies outer DSCP from WLAP to 802.1p (CoS) fields and sends it to the switch
  • Web interface (do you even need to know this?)
    • Controller>QoS Profiles
      • Per-User Bandwidth Contracts – set avg data rate, burst data rate, avg real-time rate, and burst real-time rate
      • Over the Air QoS
        • Maximum RF usage per AP (%)
        • Queue Depth – queue size before dropping packets
        • Wired QoS Protocol – 802.1p or None
    • Controller>WLANs>Edit
      • For each WLAN ID, set the QoS value:  plat, gold, silver, bronze
      • WMM Policy
        • Disabled – 802.11e/WMM QoS requests are ignored
        • Allowed – 802.11e/WMM QoS requests are sent
        • Required – 802.11e/WMM QoS requests are required

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