802.11

• WLANs work at physical layer and data link layer
• Support TCP/IP higher-layer OSI protocols and operating systems
• Most popular standard used by WLANs is wi-fi
  • Developed by IEEE's 802.11 committee
• Standards
  • 802.11b
  • 802.11a
  • 802.11g
  • 802.11n
  • 802.11ac
    • Operates on 5 GHz
    • Exceeds benchmarks set by earlier standards
    • First Wi-Fi standard to approach Gigabit Ethernet capabilities
• 802.11n and later modify the way frames are used at the MAC sublayer
  • Lower portion of the data link layer
• LLC sublayer is primarily concerned with multiplexing, flow and error control, and reliability

Access Method

• 802.11 MAC services
  • Append 48-bit physical addresses to frame to identify source/destination
• Same physical addressing scheme as other Ethernet networks
  • Can be easily combined with IEEE networks
• Wireless devices
  • Not designed to simultaneously send/receive
  • Cannot prevent collisions
  • Different access method than Ethernet
• CSMA/CA
  • Carrier Sense Multiple Access with Collision Avoidance
  • Minimizes collision potential
  • Uses ACK packets to verify every transmission
    • More overhead than 802.3
    • Real throughput is less than theoretical maximum
• RTS/CTS
  • Request to Send/Clear to Send
  • Ensures packets not inhibited by other transmissions
  • Efficient for large transmission packets
  • Decreases overall 802.11 efficiency

Frames

• Overhead
  • ACKs, probes, beacons
• Specifies MAC sublayer frame type
• Multiple frame type groups
  • Management frames
    • Association and re-association
  • Control frames
    • Medium access and data delivery
    • ACK and RTS/CTS frames
  • Data frames
    • Carry data sent between stations
    • Four address fields
      • Source address
      • Transmitter address
      • Receiver address
      • Destination address
    • Sequence control field
      • How large packets are fragmented
    • Error checking and fragmentation are handled at the MAC sublayer of the data link layer

Innovations

• MIMO
  • Multiple Input Multiple Output
  • Multiple access point and client device antennas may issue signal to one or more receivers
  • Increase range and network's throughput
• MU-MIMO
  • Multiuser MIMO
  • Newer tech that allows multiple antennas to service multiple clients simultaneously
  • Reduces congestion
  • Contributes to faster data transmission
  • Available with WAVE 2 802.11ac products
• Channel bonding
  • Two adjacent 20 MHz channels can be bonded to make a 40 MHz channel
    • More than doubles bandwidth available in a single 20 MHz channel
• Frame aggregation
  • Combine multiple frames into one larger frame
  • Two techniques
    • A-MSDU (Aggregated Mac Service Data Unit)
    • A-MPDU (Aggregated Mac Protocol Data Unit)
  • Reduces overhead

Computer Science Networking Wireless Networking