anthony morris
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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
  • 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

802.11 data from compared with an 802.3 Ethernet frame

  • 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