9. Mixed WLAN - Broadcom implementations

The real test of draft-11g implementations is how they handle WLANs with both draft-11g and 11b active stations. Part 1 gave you a taste of how Broadcom handles this complex juggling act. I'll now show a few more examples, including how Intersil handles mixed networks.

Figure 14 shows a test done with original firmware using the Broadcom-based Buffalo Tech WBR-G54 router and Buffalo WLI-CB-G54 draft-11g and ORiNOCO Gold 11b clients. The Buffalo Tech card starts first, and is joined by the ORiNOCO card at the 20-second mark. Both cards run until the Buffalo Tech card completes its programmed number of transfers and stops, letting the ORiNOCO card finish by itself.

Figure 14: Buffalo Tech Original - WLI-CB-G54 & ORiNOCO Stations
(click on the image for a full-sized view)

The results show that the draft-11g client throughput drops to a lower "Level 3" value once the 11b station becomes active, but that the 11g client and 11b client appear to share their time together relatively well. Note that the Buffalo Tech client's throughput is slightly greater than the ORiNOCO's.

Figure 15 shows the same test, but this time run with the latest available Buffalo Tech AP firmware.

Figure 15: Buffalo Tech New - WLI-CB-G54 & ORiNOCO Stations
(click on the image for a full-sized view)

Once again, the Buffalo Tech and ORiNOCO clients work well together and appear to have almost equal throughput while both are active. But although you might think that all Broadcom implementations are equal, the next tests using Linksys gear will show that you'd think wrong!

Figure 16 shows a similar test run as before, but this time using a Linksys WAP54G AP and WPC54G draft-11g and NETGEAR MA401 11b clients. The WAP54G is running its original firmware.

Figure 16: Linksys Original - Linksys WPC54G & NETGEAR MA401 Stations
(click on the image for a full-sized view)

This time, you can see that the Linksys client gets the raw end of the throughput deal, dropping below the MA401. The effect on the Linksys client was so severe, that if I hadn't been running Chariot and been able to see that it was still running, I probably would have thought that the transfer had hung.

I next switched in the Linksys WRT54G router that had the latest available Broadcom firmware and reran the same test. (I set up the router as an access point so that the router's throughput wouldn't get in the way of the measurement.)

Figure 17: Linksys New - Linksys WPC54G & NETGEAR MA401 Stations
(click on the image for a full-sized view)

Figure 17 shows that performance has changed, but not really in the direction it's supposed to! With the new firmware, the 11b NETGEAR card looks like it's not only still getting better throughput than the Linksys card, but also higher throughput than before!

This indicates to me that the Broadcom firmware hasn't yet implemented the changes mandated in the 6.1 version of the 802.11g draft spec, which dictate that 11g stations get more time on the air than 11b stations. A recent conversation with Broadcom confirmed that draft 6.1 changes weren't incorporated into the firmware versions that I tested, since Broadcom said they had released their "6.1" firmware to their customers only within the last week or so.

So how about Intersil? Do they handle active draft-11g and 11b clients any better?