802.11


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802.11

Commonly known as "Wi-Fi," the IEEE 802.11 standards provide the wireless counterpart to Ethernet, and the Wi-Fi Alliance certifies products. All versions use OFDM encoding except for the earlier 802.11b, which uses DSSS (see OFDM and spread spectrum). For details about each standard, see table below and 802.11 versions.

Infrastructure and Ad Hoc Modes
In "infrastructure" mode, Wi-Fi devices transmit to an "access point" (base station), which may be a stand-alone unit or built into a wireless router. In "ad hoc" mode, two wireless devices communicate peer-to-peer without an access point in between. Another direct connection mode is also available (see Wi-Fi Direct).

Throughput Varies
Speed is distance dependent. The farther away the device from the base station, the lower the speed. Also, the actual throughput is generally half of the rated speed because 802.11 uses collision "avoidance" (see CSMA/CA) rather than Ethernet's collision "detection" method (see CSMA/CD). For example, a rated 54 Mbps may yield 27 Mbps in real data throughput. For more about Wi-Fi networks, see wireless LAN and Wi-Fi. See Wi-Fi hotspot, 802.11 timeline, wireless router, ISM band, 802.16 and 802.15.

    802.11 SPECIFICATIONS              Max    Indoor  Channel    Bands   Speed   Range*   Width    (GHz)   (Mbps)  (ft)     (MHz)11ac      5  433***  230   20/40/80/160
 11n  2.4, 5  150**   230   20/40
 11a       5   54      95   20
 11g  2.4      54     170   20
 11b  2.4      11     150   20

   * = Up to 4x farther outdoors.
  ** = Per antenna at 40 MHz channels.
 *** = Per antenna at 80 MHz channels.


Wi-Fi Access Points
Wi-Fi devices transmit to central base stations called "access points" (APs), such as these ceiling-mounted and desktop examples (bottom). The circuitry in an access point is also built into a wireless router.


Wi-Fi Access Points
Wi-Fi devices transmit to central base stations called "access points" (APs), such as these ceiling-mounted and desktop examples (bottom). The circuitry in an access point is also built into a wireless router.







Wi-Fi Adapters
The adapter (top) adds Wi-Fi to any computer via USB, while the card on the bottom plugs into a PCI slot inside a desktop computer. (Images courtesy of D-Link Corporation and TP-LINK Technologies Co., Ltd.)
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