Draft-11g and "Legacy" 802.11b
Revised March 10, 2003
This class of interoperability is due to problems caused by some older 802.11b products. It includes the Short Preamble related issues that I covered in Part 1, but also a misaligned data rate issue. This second problem comes from the fact that some 802.11b devices don't know what to do when confronted with draft-802.11g stations advertising data rates other than the 1,2, 5.5 and 11Mbps supported by 802.11b devices. This problem initially prevented Cisco 340 and 350 cards from associating, i.e. connecting, with draft-11g APs. But most vendors have released firmware updates that fix the problem, so you probably won't see it unless you have early-vintage product (Dec 2002 / Jan 2003) with original firmware.
I'm told that the IEEE Task Group g is aware of both issues and will probably be addressing them in future drafts or the final spec. In the meantime, product vendors have either already patched their firmware and drivers to fix these issues, or will do so shortly.
Note that with all the flavors and vintages of 802.11b equipment out there, I'd be hard pressed to say with absolute certainty that real, functional-failure-type problems in this category don't exist. But I can say that in my testing using 802.11b products based on Intersil PRISM II, TI ACX-100, Agere Systems, and Atheros 5100X chipsets, I've yet to run across a situation where a draft-11g product, based on either the Broadcom or Intersil chipsets, would not associate and successfully transfer data.