维基如是说 In June 2003, a third modulation standard was ratified: 802.11g. This works in the 2.4 GHz band (like 802.11b), but uses the same OFDM based transmission scheme as 802.11a. It operates at a maximum physical layer bit rate of 54 Mbit/s exclusive of forward error correction codes, or about 22 Mbit/s average throughput.[13] 802.11g hardware is fully backward compatible with 802.11b hardware and therefore is encumbered with legacy issues that reduce throughput when compared to 802.11a by ~21%.
The following are the most commonly used wireless network technologies: ■ 802.11b The original and still most common wireless network type. 802.11b advertises a theoretical network throughput of 11 Mbps, but 3–4 Mbps is more realistic. Because 802.11g and 802.11n are backward-compatible with 802.11b, an 802.11b client can connect to almost any network (albeit at the slower 802.11b speed).
NOTE 802.11 An 802.11 standard preceded 802.11b, but it was never widely used.
■ 802.11g An update to 802.11b that advertises a theoretical network throughput of 54 Mbps (with 10–15 Mbps realistic bandwidth under good circumstances). You can use 802.11g network access points in one of two modes: mixed (which supports 802.11b clients but reduces bandwidth for all clients) or 802.11g-only (which does not support 802.11b clients but offers optimal bandwidth). ■ 802.11n An update to 802.11g and 802.11b that provides improved range and performance claims of 250 Mbps (with a much smaller realistic bandwidth). In addition to providing backward compatibility with 802.11b and 802.11g, this standard is backward compatible with 802.11a. As of the time of this writing, 802.11n has not yet been standardized; however, many vendors have offered wireless access points with support for “pre-N” standards.————————(Here means aroung year2008~2009.——俺注) ■ 802.11a An old standard that uses the 5.4 GHz range instead of the 2.4 GHz range used by 802.11b, 802.11g, and 802.11n. 802.11a originally competed with 802.11b, but it was not as popular and has now been largely abandoned. Many vendors offer wireless access points that include proprietary extensions that offer better network performance when used with wireless network adapters from the same vendor. Although these proprietary extensions can improve performance, they don’t work with network adapters made by other vendors.
■ 802.11g An update to 802.11b that advertises a theoretical network throughput of 54 Mbps (with 10–15 Mbps realistic bandwidth under good circumstances