Scenario 2 - 11b associated, but idle
As I've discovered while testing both Broadcom and Intersil-based draft-802.11g products, the trend is definitely toward implementing automatic and what I call "adaptive" 802.11b protection. This method of protection yields higher throughput in what appears to be a protection "standby" or "sniffing" mode, when there are no 802.11b stations in range. Throughput drops noticeably, though, once an 11b client is detected and associates with the AP. Figure 10 provides two examples of this behavior.
Figure 10: WAB501 vs. ORiNOCO Temporary Association
The screen shot shows the effect from the temporary association of two different 802.11b clients on a throughput test running between the WRT54G and a WPC54G client. During each Chariot run, I plugged an 802.11b client into a second laptop sitting close by at about the 20 second point in the test run. I then shut down and removed the 11b card at about the 50 second mark.
The bluish plot shows the throughput effect from the temporary association of a NETGEAR WAB501 Dual-Band CardBus card (Atheros 5100X-based), and the reddish plot the effect from an ORiNOCO Gold client. Although both cause a throughput drop at about the same time, the effect from the WAB501's association goes away seconds after I shut down and remove the card. But throughput doesn't recover from the ORiNOCO's association until about a minute after I remove the card.
The main points here are:
The throughput of your draft-11g WLAN will drop when even one 802.11b client comes into range and associates with your access point or wireless router
The lowered throughput can remain in effect for minutes after 11b clients leave your WLAN.
I expect that manufacturers will be tuning their algorithms to minimize both effects, but you should expect lower throughput when 802.11b clients are present in your draft-802.11g WLAN, at least until manufacturers stop tweaking their protection algorithms.