802.11b Interoperability
I then checked the handling of simultaneous normal 802.11b and draft 11g traffic. Again using Chariot, I set up a test using two client pairs. The reference draft 802.11g test pair for each test was a WinXP Home Dell Laptop with Linksys WPC54G Cardbus card to Win98SE Ethernet client. The second pair used a WinXP Home Compaq Presario 1650 Laptop with various 802.11b cards to a different Win98SE Ethernet client.
In an attempt to hit the major chipset types, I tested the following cards:
- NETGEAR MA401 (Original Intersil PRISM II based card)
- ORiNOCO Gold (Agere Systems chipset)
- D-Link DWL-650+ (TI ACX100 chipset)
- NETGEAR WAB501 (Atheros 5100X dual-band chipset)
In each test, I started the Linksys card first, then kicked in the 802.11b card. Both cards then run simultaneously for awhile, with the Linksys card stopping first to let the 11b card finish by itself. As Figures 7-10 show, the results were very interesting!
Figure 7: Two pair test – NETGEAR MA401
(click on the image for a full-sized view)
Figure 8: Two pair test – ORiNOCO Gold
(click on the image for a full-sized view)
Figure 9: Two pair test – D-Link DWL-650+
(click on the image for a full-sized view)
Figure 10: Two pair test – NETGEAR WAB501
(click on the image for a full-sized view)
The plots show that in all cases except for the NETGEAR WAB501, the Linksys card virtually grinds to a halt while the 802.11b card is running. But for some reason, it’s the WAB501 that takes the hit when paired with the Linksys card. It not only pretty much stops while the WPC54G is running, but never gets much above 2Mbps even after the Linksys card finishes its run! The plots also show that neither the Intersil PRISM nor Atheros AR5001X-based NETGEAR cards ever achieve their normal 5Mbps throughput, even when they’re allowed to run alone.
These results were pretty disturbing because they not only indicate that the WAP54G has problems with mixed-mode (802.11b and draft-11g) bandwidth sharing, but that it also does not properly function as an 802.11b-only Access Point!
Fortunately (I think!) Linksys’ Wireless-G product manager confirmed my findings and said that they were due to the newer Broadcom AP and client firmware that they were using. This newer firmware improved some of the draft-11g issues that I had found with the BuffaloTech product, but had the not-so-good effects that I was seeing with 802.11b interoperability. He assured me that Linksys was not satisfied with the 11b issues and was hard at work with Broadcom on new firmware to fix them.
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