Now that I saw what Broadcom could do, I turned my attention to Intersil. Since WLAN equipment manufacturers have yet to release WPA drivers for any Intersil-based products, I went directly to Intersil for help.

They supplied me with a number of goodies that enabled me to look at their WPA-enabled performance. I first tried their PRISM Duette (a/b/g) Cardbus Reference Design with an AP reference designed based on Ubicom's IP2022 Internet Processor and an Intersil PRISM GT CardBus radio. Figure 12 tells the tale.

Figure 12: Intersil Duette CardBus Reference Design Client and
Ubicom IP2022 / Intersil GT Reference Design AP
Condition 1 Throughput vs. Security modes
(click on image for a larger view)

The throughput variation makes it hard to separate out WEP and WPA effects, but since the worst-case difference in average throughput is only about 4% between no security and WPA-PSK / TKIP, I'd have to say that's within the accuracy of my measurement and conclude there's basically no throughput hit for enabling either WPA TKIP or WEP with these designs.

Note that there's no plot for WPA - AES. That's because even though the hardware supports AES hardware acceleration, Intersil has decided to stick with the WPA spec and not enable it at this time. Doesn't look like they need it to keep throughput chugging right along, either!

WPA in action - Intersil 11b Performance

Intersil has a considerable installed base of earlier PRISM-based 11b products, so I was especially interested to see whether enabling WPA on older 11b products would cause a considerable throughput reduction. I'm happy to report that it doesn't - at least for the test cases I tried!

Figure 13: Linksys WPC11v3 11b Client and Intersil 11b WPA Reference AP
Condition 1 Throughput vs. Security modes
(click on image for a larger view)

Figure 13 shows the results from tests using a Linksys WPC11v3 11b Client and Intersil 11b WPA Reference AP. The AP is the same design used by the Wi-Fi Alliance as part of its WPA certification test bed, and I used the WPA driver that was part of Linksys' first WPA update release a few weeks ago.

I was very pleasantly surprised by these results, but perhaps I shouldn't have been, given the WPC11v3's use of Intersil's last 11b-only PRISM 3 chipset. So I decided to also run the PRISM 2.5 Reference design card that Intersil supplied and that's the other half of the Wi-Fi Alliance testbed. Maybe the older chipset would suffer some performance hit?

Figure 14: Intersil PRISM 2.5 Reference 11b Client and Intersil 11b WPA Reference AP
Condition 1 Throughput vs. Security modes
(click on image for a larger view)

Figure 14 again shows throughput difference within the limit of my measurement. I couldn't go back to a PRISM 2-based design because I didn't have WPA drivers (although Intersil has made them available to their customers for incorporation into end products).

So it looks like Intersil did a good job with their WPA implementation for their 11b chipsets. Now if only manufacturers will do the work they need to do and get their WPA driver upgrades finished and posted for download!