Mixed WLAN - More Station Association
Further experiments showed that different 802.11b clients had varying effects on the draft-11g test pair's throughput when they temporarily associated with the draft-11g AP.
Figure 9: Intersil New - WAB501 vs. ORiNOCO Temporary Association
(click on the image for a full-sized view)
Figure 9 uses the Intersil-based draft-11g test pair and once again shows the throughput effect from the temporary association of a WAB501 client. But this time it also overlays the effect from the temporary association of 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. I found a similar effect from the temporary association of Intersil PRISM II and TI ACX-100 based clients.
This delayed-recovery effect isn't limited to Intersil, either. Figure 10 shows the results from the same pair of tests as shown in Figure 9, but run with the Linksys WRT54G / WPC54G pair instead.
The plot again shows a quick recovery from the temporary association of the NETGEAR WAB501 client, but that it takes about three minutes for the Linksys pair to switch back to its maximum throughput "standby" protection mode.
I ran similar tests with both Intersil and Linksys/Broadcom test pairs and other 11b clients, and found that the Atheros-based NETGEAR WAB501 was the only 11b client that consistently allowed a fast recovery to the "Level 1" throughput mode.
The other observation worth noting is that I could clearly see that the drop to the Level 2 throughput didn't take place until the 11b client was actually associated with the draft-11g AP under test. I could see quick throughput "dropouts" during the association process, but only a successful association caused the switch to the lower "Level 2" state.
I'll next look at what happens when you try to ignore 11b stations!