Last Post: May 12, 2009:
I apologize, but you are incorrect about the data rates.
11g supports 12 data rates as you know. "11g only mode" isn't even covered in the standards, but what it generally means (it varies somewhat among vendors) is that it won't allow 11b devices to associate, but it will still communicate with other 11g devices at DSSS data rates.
An 11g device in "11g only mode" will communicate at all data rates, but only to devices that support OFDM data rates (11g devices).
There is a common misconception about basic data rates. A basic data rate means that, if you are going to communicate with the AP, you must be able to communicate at these data rates, but it is not REQUIRED to ALWAYS communicate at those data rates. It will still go up to, and down to all SUPPORTED data rates.
On to your multicast situation. Yes, if your AP is in protection, it will transmit a CTS-to-Self at the appropriate DSSS data rate and then transmit the multicast data frame at whatever OFDM data rate is appropriate for the PHY, up to 54Mbps.