802.11a


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802.11a

(networking)
A radio-based LAN protocol which speaks OFDM at 5GHz, one of the two wi-fi protocols.
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802.11

The Wi-Fi standards. IEEE 802.11 standards cover every version of Wi-Fi, and the Wi-Fi Alliance, certifies products. Wi-Fi is the wireless counterpart to "wired" Ethernet, and Wi-Fi and Ethernet co-exist in every home and business.

All versions of 802.11 use OFDM encoding except for 802.11b, which uses DSSS (see OFDM and spread spectrum). For details about each standard, see 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 devices communicate peer-to-peer without an access point in between (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  ChannelWi-Fi   Bands Speed   Range*   Width No.    (GHz) (Mbps)  (ft)     (MHz)1 11b  2.4      11    150  20
 2 11a       5   54     95  20
 3 11g  2.4      54    170  20
 4 11n  2.4, 5  150**  230  20/40
 5 11ac      5  433*** 230  20/40/80/160
 6 11ax 2.4, 5  600*** 230  20/40/80/160

  ** = Per antenna at 40 MHz channels.
 *** = Per antenna at 80 MHz channels.


Stand-Alone Access Points
Wi-Fi access points (APs) are central base stations with antennas. These examples are stand-alone APs (ceiling mounted and desktop). They are generally not found in homes because an AP is already built into the wireless router.


Stand-Alone Access Points
Wi-Fi access points (APs) are central base stations with antennas. These examples are stand-alone APs (ceiling mounted and desktop). They are generally not found in homes because an AP is already built into the 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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