From my previous testing, I've reached the conclusion that it's a lose-lose deal to run a WLAN with a mixture of draft 11n and 11g clients. You would think that with typically around 70 or 80 Mbps of usable bandwidth that there would be plenty to spare so that both clients didn't noticeably suffer. But, unfortunately, that hasn't been the case in the past, and the 600N is no exception.
I set up my usual test using a second notebook with a Linksys WPC54G V3 11b/g card (Broadcom chipset). Both it and the Fujitsu notebook with WPC600N card were associated with the 600N, which was set to its 2.4 GHz Standard - 20 MHz Channel mode, to simulate what should be its proper "out of the box" settings. I then ran two IxChariot throughput.scr streams, alternating the STA that got on the air first.
Figure 27 shows how uplink throughput was shared when the 11n pair started first, while Figure 28 shows the 11g pair starting first.
Figure 27: Mixed 11n, 11g STAs - Uplink, N starts first
The results follow the pattern that I've seen with other draft 11n products,i.e. the 11g STA gets knocked down to 11b speeds. In this case the 11g throughput is knocked down to about 4 Mbps from its normal 20 Mbps or so, or about 80%. The 11n pair also gets a throughput hit, but still manages to run at about 50 Mbps when the 11g STA is on the air.
Figure 28: Mixed 11n, 11g STAs - Uplink, G starts first
The 11g client does a little better running downlink since it manages to run at around 11 Mbps when sharing the air with the WPC600N.