The IEEE 802.11g standard was published (finalized) in July 2003. It
provides the same theoretical maximum speed as 802.11a, which is 54 Mbps, but
operates in the same 2.4 GHz spectrum as 802.11b. Unlike 802.11a, 802.11g is
backward compatible with 802.11b. Interoperability among and between all speeds
exists, so the entire WLAN does not need to be upgraded when moving to higher
speeds. The operating data rates for the different 802.11 standards, along with
the frequency band and modulation used, are summarized in Figures
and
. 802.11g
is expected become the standard of choice over 802.11b.
The 802.11g
standard requires the use of OFDM for fast data rates (greater than 20 Mbps),
as well as backward compatibility with 802.11b CCK encoding. The standard
utilizes a hybrid architecture to provide backward compatibility. Even though
legacy 802.11b devices will not be able to decode the packet payload of these
frames, they are able to "sense" them on the network. The new frames
can coexist with 802.11b, similar to the way 802.11b can coexist with older, 2
Mbps 802.11 systems. The pure OFDM specification, which uses a more efficient
OFDM-based preamble/header, does not have the same characteristics. 802.11b
devices will not sense 802.11g frames, and vice-versa. By taking advantage of
the RTS/CTS elements of IEEE 802.11, in which access points speaking both
languages can regulate the transmissions, the two can coexist peacefully.