Hardware Reference
In-Depth Information
to 54Mbps) and helps avoid interference from devices that cause interference with lower-frequency
802.11b networks. Although real-world 802.11a hardware seldom, if ever, reaches that speed
(almost five times that of 802.11b), 802.11a relatively maintains its speeds at both short and long
distances.
For example, in a typical office floor layout, the real-world throughput (always slower than the rated
speed due to security and signaling overhead) of a typical 802.11b device at 100 feet might drop to
about 5Mbps, whereas a typical 802.11a device at the same distance could have a throughput of
around 15Mbps. At a distance of about 50 feet, 802.11a real-world throughput can be four times
faster than 802.11b. 802.11a has a shorter maximum distance than 802.11b (approximately 75 feet
indoors), but you get your data much more quickly.
Given the difference in throughput (especially at long distances), and if we take the existence of
802.11g out of the equation for a moment, why not skip 802.11b altogether? In a single word:
frequency . By using the 5GHz frequency instead of the 2.4GHz frequency used by 802.11b/g,
standard 802.11a hardware cuts itself off from the already vast 802.11b/g universe, including the
growing number of public and semipublic 802.11b/g wireless Internet connections (called hot spots )
showing up in cafes, airports, hotels, and business campuses.
IEEE 802.11a, like 802.11b, is obsolete in new installations. However, 802.11n network adapters
that support the optional 5GHz frequency can interconnect with 802.11a adapters, and many late-
model 802.11a adapters also support 802.11b or 802.11g (2.4GHz) frequencies.
802.11g
IEEE 802.11g, also known to some as Wireless-G , is a standard that offers compatibility with
802.11b along with higher speeds and better security. It runs at speeds up to 54Mbps, the same as
802.11a, but supports the same 2.4GHz frequencies as 802.11b. The final 802.11g standard was
ratified in mid-2003.
802.11g supports two standard data-encoding methods:
• QPSK/CCK (same as used by 802.11b), which enables 802.11g to connect with 802.11b
devices, albeit at the same 11Mbps maximum speed as Wireless-B
• OFDM (same as used by 802.11a, but in the 2.4GHz band); this method is used for connections
at the maximum 54Mbps speed of Wireless-G
Optional data-encoding methods supported by 802.11g include Packet Binary Convolutional Coding
(PBCC-22), which supports speeds ranging from 6 to 54Mbps and CCK-OFDM, a method originally
used by proprietary 22Mbps versions of 802.11b, and limited to 22Mbps with 802.11g.
Note
Optional data-encoding methods are not supported by all 802.11g hardware.
Although 802.11g is designed to connect seamlessly with existing 802.11b hardware, early 802.11g
hardware was slower and less compatible than the specification promised. In some cases, problems
with early-release 802.11g hardware can be solved through firmware or driver upgrades.
Note
Although 802.11b/g/n wireless hardware can use the same 2.4GHz frequencies and can coexist
 
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