802.11b Interoperability
As I pointed out earlier, the WG602 does not have any sort of mode setting and uses automatic and what I call "adaptive" 802.11b protection. This yields a three-tiered throughput characteristic with the three tiers being:
- Without any 802.11b clients active
- With an 802.11b client associated to the same draft-802.11g access point or router, but idle
- With an 802.11b client active, i.e. transmitting data simultaneously with 802.11g data
I ran interoperability tests to check the last two conditions using 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)
Figures 9 and 10 show two examples of the effect from the temporary association of different 802.11b clients on a throughput test running between the WG602 and WG511 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 40 second mark.
Figure 9: Association test - NETGEAR MA401
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Figure 10: Association test - NETGEAR WAB501
NOTE SHORTER TIME SCALE!
(click on the image for a full-sized view)
Although both tests have a throughput drop at about the same time when the card associates with the AP, 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 MA401's association until about a minute after I remove the card. I'm not including the plots from the D-Link and ORiNOCO tests because they were essentially the same as what you see in Figure 9. I expect that Intersil will be tuning their algorithms to minimize the recovery time, but for now, you can see that effects of an 802.11b card associating with your WG602 may linger a little bit after it leaves.
My second round of 11b interoperability testing 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 NETGEAR WG511 Cardbus card to Win98SE Ethernet client. The second pair used a WinXP Home Compaq Presario 1650 Laptop with the same four 11b card types as before to a different Win98SE Ethernet client.
In each test, the WG511 started first, followed by the 802.11b card after 20 seconds. Both cards then run simultaneously for awhile, with the WG511 stopping first to let the 11b card finish by itself. Figures 11 and 12 show the worst and best cases of my four test runs.
Figure 11: Mixed mode test - ORiNOCO Gold
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Figure 12: Mixed mode test - NETGEAR WAB501
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As I said earlier, although Broadcom-based products may have the edge on best-case throughput, NETGEAR's Intersil-based gear handles mixed draft-11g / 11b WLANs much more gracefully. A key difference from present Broadcom-based products is that the WG602 looks like it's really implementing the changes mandated by version 6.1 of the 802.11g draft spec, which says that 11g stations (clients) will be treated with higher priority than 11b clients.
Figure 12 clearly shows a wide separation in draft-11g and 11b throughput while both an Atheros-based NETGEAR WAB501 dual-band card (forced to 11b mode) and the WG511 are running. But Figure 11 shows that there still is room for improvement since when an ORiNOCO Gold client is used, the WG511 is forced down to approximately the same throughput rate. The tests results from the D-Link DWL-650+ and NETGEAR MA401cards were similar to Figure 11, but with higher throughput variation for the WG511 when paired with the Intersil PRISM 2-based NETGEAR MA401.