Wireless Crib Notes

These are my ‘crib notes’ that I’ve made to serve as a last minute refresher. Please forgive the grammer / spelling as I did not develop these notes with publishing in mind.

Wireless                                                                                                                                                              23/06/09

*** Theory ****

  • WLAN – Is called a Basic Service Set BSS (Hub and Spoke). Area of coverage is called a Cell. Device associate with the wireless device. They are half duplex so uses CSMA/CA.
  • SSID – Service set identifier is case sensitive and up to 32 char.
  • AP – Access point aka WAP. Client can use to find AP;
    • Active scanning – Client sends probe request frames & wait for response
    • Passive scanning – Listens for beacons frames from AP. No probes sent
    • Authentication
      • Open system
      • Shared key  – like WEP, WEP can be hacked easily.
        • EAP/LEAP – EAP or LEAP. Leap is cisco only. It has 2-way auth between AP and client, AP uses RADIUS to auth client, Keys are dynamic (generated per authentication), not static. Better than WEP
        • WPA/WPA2 –
        • AD HOC WLAN – aka IBSS
        • Ranges
          • 802.11a – 25MBPS but can reach 54MBPS. Indoor range 100 ft. 5GHZ
          • 802.11b – 6.5MBPS upto 11MBPS. 100 ft. 2.4GHZ
          • 802.11g – 25MBPS to 11 MBPS. 100 ft. 2.4GHZ. Compatible with g hence b/g
          • 802.11n – 200MBPS upto 540MPS, 160 ft. 2.4 or 5 GHZ
          • Microwave can cause issue as it uses 2.4 GHZ band
          • Antenna
            • Yagi Antenna – Sends signal in a single direction only. (P2P) BETWEEN AP
            • Omni – Sends signal to all directions (P2M) BETWEEN AP AND HOSTS
            • Cisco Unified Wireless Network – WLAN Contoller. Talks to LAP (Lightweight Access Point) via LWAPP (Lightweight Access Point Protocol) to make policy consistent. It a centralised Authority.
            • Aironet tray utility