Legacy Neighbor WLAN Tests
My last set of tests checked the Clear Channel Assessment (CCA) mechanism that is supposed to ensure "neighbor friendly" operation with legacy WLANs. (See this page for an explanation of CCA).
For this test, I configured the 600N as an AP, set to Auto mode, Standard Channel 1 and no encryption. This made Channel 1 the primary channel and Channel 5 the extension.
I then set up a second wireless LAN using a Linksys WRT54G router (original rev) and WPC54G V3 CardBus card. The WRT54G had most recent firmware and was set to its default Mixed mode and Channel 5—the extension channel. I also operated it as an AP and connected it to the same switch that the 600N was connected to.
Two IxChariot throughput.scr scripts were used to drive traffic to both 11n and 11g test pairs. I tested both uplink and downlink traffic and alternated between having the 11n and 11g WLANs start first. (If you need a diagram of the test setup, this one showing a similar test setup should give you the basic idea.) I also used the Cognio Spectrum Expert to monitor spectrum use.
Figure 29: CCA Test - Downlink, N starts first
As has been the case with all other Draft 2.0 11n products, the 11n products dominate and severly reduce the throughput of the 11g WLAN operating on the extension channel. Spectrum monitoring shows that the 11n WLAN continues to operate with 40 MHz of bandwidth, regardless of 11g WLAN activity.
I have to say that the 600N seems a bit better than other products in that it doesn't completely knock the 11g WLAN off the air, as shown in Figures 29 and 30. But there is still no evidence that the 600N switches to 20 MHz channel mode when there is a legacy WLAN operating in its extension channel.
Figure 30: CCA Test - Downlink, G starts first
Regular readers will know that I recommend spending the extra bucks for dual-band when it comes time for you to make the move to draft 11n. While manufacturers are offering dual-band single-radio models at slightly lower price points, two radios make the most sense if you're going to have a one-router setup. The relatively small cost savings pales in light of the greatly enhanced flexibility provided by two radios.
Some buyers seem to share my opinion, given the frequent frustrated inquiries I have gotten during the past year about the availability of the dual-band, dual-radio D-Link DIR-855, which has yet to ship. Perhaps now that Linksys has finally decided to go to market, D-Link will soon follow suit.
But, for now, there are only two dual-band draft 11n players on the field since Buffalo is, I hope, only temporarily sidelined by its CSIRO woes. Both the Apple Airport Extreme and the 600N have similar feature sets, including NAS functions if you add an external USB drive. And both are equal enough in routing and wireless performance to have the decision boil down to a cost / benefit tradeoff.
If you really need simultaneous dual-band draft 11n today, the 600N should serve your needs well. But I'd wait a bit if you can, since it looks like the next 3 - 6 months will see more dual-band products appear. It will also give Linksys some time to get out a firmware rev or two to smooth the rough edges in an otherwise good product.