Final 802.11g draft standard squeezes data rates

The Institute of Electrical and Electronics Engineers (IEEE) has approved a final draft standard for 802.11g wireless Lans that...

The Institute of Electrical and Electronics Engineers (IEEE) has approved a final draft standard for 802.11g wireless Lans that will have a true throughput for internet-type connections of between 10Mbit/sec and 20Mbit/sec, far lower than 54Mbit/sec raw data rate initially billed for the standard.

The standard was approved by the IEEE on 15 May, but will not be made publicly available until members of the IEEE 802.11 working group ratify it next month.

Sheung Li, a product line manager at Atheros Communications, a Wlan chip manufacturer, said the lower actual versus raw data rates for 802.11g arose from the need to assure backward compatibility with millions of existing 802.11b Wi-Fi client devices and access points that operate in the same 2.4-GHz frequency band.

The 802.11g standard includes built-in protection mechanisms to ensure that the devices do not interfere with older 802.11b devices. That means the "g" systems will need to transmit an electronic warning to "b" devices that a "g" device is operating, a warning that is enough to cause a cutback in actual throughput, Li said. 

Li estimated that that in mixed 802.11b and 802.11g networks running standard TCP/IP Internet protocols this will reduce actual throughput to 10Mbit/sec. - while pure 802.11g networks will have actual data rates of around 20Mbit/sec.

Li pointed out that even at these data rates the 802.11g devices still outperform 802.11b devices, which have a raw data rate of 11Mbit/sec but an actual throughput of about half that speed. 

Pat Hurley, an analyst at TeleChoice in Boston, said companies looking for higher speeds from their Wlans should consider using hardware based on the 802.11a standard, which provides a real data rate of about 24Mbit/sec in the 5-GHz band. Hurley added that companies starting from scratch could consider a combined 802.11a/g network, which would offer two options for high data rates in a campus environment as well as the ability to access 802.11b hot spots while on the road - since 802.11g clients can operate with 802.11b access points. 

However, 802.11a devices operate in a different frequency band than the "b" and "g" devices, meaning they are not compatible with them. 

Atheros has already shipped prestandard 802.11g chip sets to Wlan manufacturers. 

Jeff Abramowitz, director of wireless Lan marketing at Broadcom, which supplies Wlan chip sets for PC cards used by Dell, said end users of prestandard Broadcom 802.11g chips will also need to download new drivers to make their older gear compatible with the final IEEE standard. 

Apple Computer has also released devices using the 802.11g standard, and has promised that its customers would be able to upgrade to the final standard once it was in place. 

Bill Carney, director of wireless Lan marketing at Texas Instruments, said his company has decided to wait until the IEEE ratifies the 802.11g standard. He expected to start shipping standard-compliant chip sets in July. 

Brian Grimm, spokesman for the Wi-Fi Alliance, said the alliance expected to start testing and certifying 802.11g products in June.

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