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

Aaron Conaway

I shake my head around sometimes and see what falls out. That's what lands on these pages. If you have any questions, the best way to contact me is through Twitter at @aconaway.

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