Final 802.11g draft standard throttles data rates down

The lower throughput is needed to protect 802.11b WLAN gear

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

The standard was approved by the IEEE on May 15 but won't be made publicly available until members of the IEEE 802.11 working group ratify it next month, according to Sheung Li, a product line manager at Atheros Communications Inc., a Sunnyvale, Calif-based WLAN chip manufacture.

Li said the lower actual vs. 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 don't interfere with older 802.11b devices. That means the 11g systems will need to transmit an electronic warning to 11b devices that a 11g 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.

Randy Conklin, director of operations for Broadband Central, a wireless Internet service provider based in Draper, Utah, that serves seven western states with a network built around wireless LAN gear, said the10Mbit/sec. data rate for 802.11g isn't good enough for advanced applications such as voice over IP or video. To support those applications, Broadband Central would need at least 20Mbit/sec. data rates, he said. As a result, the service provider will look to deploy pure 802.11g service offering the faster data rates.

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 said 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 11b and 11g devices, meaning they aren't compatible with them.

Atheros has already shipped prestandard 802.11g chip sets to WLAN manufactures, such as D-Link Corp. in Taipei, Taiwan. Li said end users would only need to download a software driver to update their 802.11g cards with the new standard.

Jeff Abramowitz, director of wireless LAN marketing at Broadcom Corp. in Irvine, Calf., which supplies WLAN chip sets for PC cards used by Dell Computer Corp., 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.

Another computer maker, Apple Computer Inc., has also released devices using the 802.11g standard -- and has promised that its customers will also be able to upgrade to the final standard once it's in place.

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

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

Copyright © 2003 IDG Communications, Inc.

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