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If using an .11n AP and having .11g and .11n client linked to it, will the AP communicate to the N client
using all G rates with no N rates? Or will it communicate N rates to the N client and G rates to the G client?

I understand the .11N AP will use RTS/CTS or just CTS for protection, but not sure what the will happen in this scenario with the RF rates.

What is the equipment you are using? Depending on the equipment and certain settings you have selected or left as default. Yes, with most equipment with default settings on, N clients will be able to use the N data rates with the AP with G clients associated. Make sure your basic rates are 802.11g compatible.

Ok,

So to take it a step further, an N AP could talk to the N client at 300Mbs (3x3, 40mhz wide) and at the same time talk to a g client at 54Mbs?

To achieve a 300Mbs connection rate both the 802.1n client and AP must be capable of 2 spatial streams, 40 MHz channel, and a short guard interval.

You can look on the client?s wifi supplicant to see what the current connection ?data? rate is.

Yes you can associate N clients at 300Mbs while G clients at 54.

The thing to remember here is that data rates are not throughput rates. You will not be able to transfer a file wirelessly at 300Mbs with the N devices or 54Mbs with the g devices.

Also remember that your 802.11 N devices will seem slower because of the G devices connected. When sending the same amount of data, the G devices will take about 6 times as long using the data rates listed above. This gives your 802.11 N devices less time to talk.

Actual throughput is hard to calculate because of the many factors. Let us pretend your network consists of only ONE 802.11N clients and ONE AP. Your upload and download speed will never be the height of the data connection rate 300MBs. Wireless is a shared medium other things besides actual data packets have to be sent as well. Beacons, Acknowledgements and so on.

So to reiterate, you can have the 802.11N 300Mbs and 802.11g 54Mbs associations rates at the same time but you will never be able to have throughput test speeds at those levels, Even if you did not have a mixed environment.

Not "at the same time"! WLANs are half-duplex. Only one device will be able to "talk". So, 11n AP will talk with each client at its own speed, but not simultaneously.