Those of you who have slogged through the entire Performance test sections of our draft 802.11n product reviews already know the "dirty little secret" that I'm about to describe. So, if you get cranky when you feel that your time has been wasted, you can move along...there's nothing here to see.
But for the rest of you contemplating taking the plunge on a year-end draft 11n upgrade, I'm going to give you a few reasons to think about keeping your current 11g router and running it along with your shiny new draft 11n purchase.
The secret is that the current crop of draft 11n consumer routers handle two things quite badly: mixes of draft 11n and 802.11g clients; and any security option other than WPA2.
Separate your N's and G's
Figures 1 through 3 show what happens when draft 11n and standard 11g clients (STAs) are both associated with a draft 11n wireless router. Figure 1 shows a D-Link DIR-655 Xtreme N Gigabit Router [reviewed] associated with its matching D-Link DWA-652 Notebook card and a Linksys WPC54G Notebook card. The DIR-655 and DWA-652 use Atheros XSPAN draft 802.11n chipsets, while the WPC54G is based on the Broadcom Airforce 802.11g chipset.
Figure 1: D-Link DIR-655 - Mixed 11n, 11g STAs - Uplink
You can see that the draft 11n and 11g STAs each take around a 50% throughput hit, which is a pretty high price to pay for using a single 11g client. At least the 11n STA gets hit only when the 11g STA is active and not when it is just associated, but idle.
Figure 2 shows a Linksys WRT600N with WPC600N Notebook card, both based on Broadcom's Intensi-fi draft 11n chipset, and the WPC54G 11g card associated. This time, the 11g STA gets knocked down to around 4 Mbps from its normal ~20 Mbps—around an 80% hit! In this case, the 11n STA fares a little better, reduced to around 50 Mbps.
Figure 2: Linksys WRT600N - Mixed 11n, 11g STAs - Uplink
The last example shows the Netgear WNR854T, which uses the Marvell TopDog draft 11n chipset. I used Netgear's recommended WN511B Notebook card in this test, which uses the Broadcom Intensi-fi chipset. Once again, 11g throughput is knocked down to around 4 Mbps—just like you used to get with 802.11b!
Figure 3: Netgear WNR854T - Mixed 11n, 11g STAs - Uplink
Note that these examples were run under best-case conditions with the STAs and wireless routers sitting in the same room only about 10 feet apart!
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