MAC: Use in Wifi & Broadband

802.11 — WiFi

• stations cannot detect collisions, relies on acknowledging to determine if collision occurred

• uses CSMA/CA (collision avoidance, not detection)

  • inserts backoff slots to avoid collisions
  • physical channel sensing:
    • sense if channel is being used
    • if yes, wait for it to be idle and then send
  • virtual channel sensing:
    • frames have a Network Allocation Vector indicating length of exchange
    • simply wait until end of transmission

• frame format:

• power saving:
  • beacon frames: client wakes up for every beacon and checks traffic map to see if there is buffered traffic that it can request
  • automatic power save delivery (APSD): access point buffers frames and sends them to client right after client sends frames, then client goes to sleep
• authentication — WEP (Wired Equivalent Privacy), then WPA (Wifi Protected Access) and WPA2

802.16 — Broadband Wireless