802.11g slows down so 802.11b can keep up.

THE LONG-AWAITED 802.11g (Wi-Fi) standard has been approved by the IEEE. The final spec was greeted with disappointment when the Wi-Fi community realized data throughput is much slower than expected, about 10 to 20Mbps compared to the claims of 54Mbps.

The disappointment is partially the result of confusion about what is being measured. The 54Mbps rate claimed for 802.11g is raw throughput that doesn't factor in the overhead of a wireless network system.

A more realistic throughput for 802.11g was 20 to 30Mbps. But that dropped to 10 to 20Mbps so 802.11g can be compatible with ubiquitous 802.11 b systems. The radios of both systems operate in the 2.4GHz range. To eliminate interference, 802.11g devices have a request-to-send/clear-to-send (RTS/CTS) mechanism that acts as a traffic cop between 11b and 11g transmissions. This slows things overall, but because it reduces interference, it is claimed to be an improvement over mixed 11b/11g networks that don't use RTS/CTS.

IEEE estimates wireless users on networks running pure 802.11g will get about 20Mbps throughput. Networks that mix 11b and 11g will get about 10Mbps through 802.11g devices. For comparison, 802.11b's raw speed of 11Mbps yields actual throughput of 4 to 6Mbps.

Installation, connection, and operation of access points are the costly aspects of Wi-Fi, so the benefit of 802.11g is that a single access point can handle both 11g and 11b mobile devices. The shorter-range but faster 802.11a doesn't have to compromise speed because it operates in the 5GHz range, but mixing 11a with 11g or 11b mobile devices requires separate 11a and 11g or 11b access points.