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Wi-Fi Router Charts

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Mesh System Charts

Click for Wi-Fi Mesh System Charts

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 6504n as an AP, set to Auto 20/40 mode, 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 6504n 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.

CCA Test - Downlink, N starts first
Click to enlarge image

Figure 18: CCA Test - Downlink, N starts first

The 6504n didn't set any new standards for "legacy friendly" behavior, but did have different performance in up and downlink directions. Figure 18 shows that the 11g WLAN gets to stay on the air, although at significantly reduced performance.

My monitoring of the spectrum during the test run showed that the 6504 kept using both channels 1 and 5. But there must have been some packet-by-packet adaptation that allowed the 11g WLAN to keep operating, as I've seen with some other products.

Figure 19 shows a very different story with both WLANs running uplink. This time, when the 11g WLAN goes active, the 11n WLAN essentially goes off-air. You can also see that even when the 11g WLAN stops transmitting, it takes around 20 seconds for the 6504n to resume transmission.

CCA Test - Uplink, N starts first
Click to enlarge image

Figure 19: CCA Test - Uplink, N starts first

I also started the 11g WLAN first and saw similar performance. So, once again, I haven't seen a draft 11n router statically fall back to 20 MHz mode when encountering a legacy WLAN in its extension channel. It also looks like Ralink has some work to do for handling neighboring legacy wireless networks.

Closing Thoughts

The 6504n is suprisingly good for a 100 buck draft 11n router, with a fast, solid routing section and no throughput penalty if you can't run with WPA2 encryption. You also get the ability to control the amount of bandwidth used in both up and downlink directions and can throttle down throughput by application, user or both. And if you're looking for bridging and repeating support, the 6504n delivers there, too.

On the downside, you don't get a gigabit LAN switch, which should be included in any draft 11n product. And, while I can't directly compare my wireless test results to the other draft 11n products I've tested, I think the 6504n falls a bit short on throughput vs. range. The user interface can also use a bit of work and the logging and documentation, as well.

If you want draft 11n on the cheap, there are plenty of options below $100. So if Edimax wants to be the low-price draft 11n leader, it has plenty of competition to beat.

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