Like 802.11a, 802.11g supports Orthogonal Frequency Division Multiplexing (ODFM) to reach a top link speed of 54 Mbps. Unlike 802.11a, 802.11g does so using the 2.4Ghz ISM band occupied by 802.11b. Sharing the ISM band lets the same radio offer higher bandwidth to newer 802.11g stations while simultaneously supporting Direct Sequence Spread Spectrum (DSSS) Complementary Code Keying (CCK) for backwards compatibility with older 802.11b stations.
If you are using a Wi-Fi Alliance-certified 802.11b router or access point (AP) in standard DSSS CCK mode, that AP will be able to associate with newer 802.11g cards that have been certified by the Wi-Fi Alliance for operation at 11 Mbps. Certifications tests verify 802.11g product interoperability at 11 Mbps with 802.11b reference implementations.
Some 802.11b and 802.11g products also implement vendor-specific "turbo" modes; interoperation in those modes is of course unlikely. The same goes for pre-standard 802.11g products released before the final standard was ratified in June 2003 -- if you have one of those cards, look for firmware upgrades that comply with the final 802.11g standard. In addition, some newer products support enhanced security using Wi-Fi Protected Access (WPA) or the Advanced Encryption Standard (AES). These new methods may not be supported by older APs, but certified WPA products are tested for their ability to negotiate down to older, less-robust security methods used by existing products.
This was first published in September 2003