Secure but Slow

But let's say that you're happy with having to sit right next to your draft 11n router and are ok with your wireless neighbors surrounding your home carrying torches and pitchforks because you've switched on the 40 MHz bandwidth mode. What happens when you enable wireless security to keep the bad guys away?

First, you can forget about throughput if you need to use WEP to accomodate any legacy clients (actually you can forget about throughput with or without security if you need to run a mixed network, but that's another story). Since WEP won't be part of the final 802.11n spec, manufacturers haven't spent much time tuning its performance.

My testing has shown a 28 to 75% reduction in throughput with WEP enabled, with the Atheros chipset turning in the highest reduction (Figure 6) and the Marvell the least (Figure 5).

Figure 5:Security mode throughput loss - downlink

But since no one would even consider running WEP today, what happens if you use WPA/TKIP? Unfortunately, draft 11n equipment makers seem to have decided to also make that an unattractive option, with throughput hits of 35 to 77%. The Atheros and Marvell chipsets again turn in the highest and lowest throughput reductions respectively (Figure 6).

Figure 6: Security mode throughput loss - uplink

So it would seem that WPA2/AES is the only way to go for draft 11n wireless security. But, even then, you'll still pay to play. WPA2/AES also throws in an additional curve with significantly different performance for down and uplink for two of the three chipsets.

The most consistent performer in both directions was the Marvell chipset coming in around 12% loss. The largest difference, 5% loss down, 35% loss up, was found with the best performer—the Broadcom chipset. The Atheros was more like the Broadcom, with 8% loss down and 28% up.

The sad thing about this is that manufacturers long ago built hardware encryption engines into their baseband/MAC chipsets in anticipation of the tougher number-crunching required by WPA/WPA2. But something seems to have been lost in the rush to 11n, and once again, the end-user pays a premium price for, in some cases, a leap backwards in performance.

I hope that this data brings anyone who is even thinking about going with an all-wireless draft 802.11n LAN to his or her senses. When the transition to 11n is finally over in 5 years or so—including a shift to the more spacious 5 GHz band for high-bandwidth applications—I'm sure the birds will be chirpier and the sun shinier. But if you need a reliable, high-bandwidth network, then wired will continue to be the only way to go.

Tags: 802.11n, WiFi,

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