9. Wireless Security

Next check was to see if enabling WEP caused any throughput degradation. I ran a Condition 1 (best case) test with 128 bit WEP enabled and disabled and found an decrease in average throughput of only 4%, which I consider to be within the bounds of my measurement accuracy. This is basically what I expected, since the TI chipset includes a hardware encryption co-processor to handle the tougher encryption that will be required in WPA2. The feature also ensures that enabling WEP has negligible effect on throughput.

Turbo mode

Although I knew that USR's 11g line wouldn't come anywhere near TI's over-hyped 100Mbps number, I ran a good number of tests to determine exactly how much TI's "802.11g+" / "packet aggregation" technology improved throughput. Figure 8 shows a comparison of the following tests run with a USR5410 card:

AP default (Dot11mode = mixed, 4x mode = Enable) 4x mode disabled Dot11mode = G only and 4x mode disabled.

Figure 8: "4X" effect comparison - USR5410 client
(click on the image for a full-sized view)

See any difference? Me neither. But I did find that enabling 4x mode helped throughput for TI-based 802.11b+ clients, as Figure 9 illustrates.

Figure 9: "4X" effect comparison - D-Link DWL-650+ "802.11b+" client
(click on the image for a full-sized view)

Figure 9 contains three test runs and shows that I needed to disable "4x" mode on both AP and client in order to get the lower throughput.

TIP: I found I had to completely uninstall my old driver and client utility for the D-Link card and do a fresh install of the latest ones that I downloaded from D-Link's support website. Otherwise I could get only about 600kbps throughput when I was occasionally able to connect to the AP.

802.11g Wireless Performance Test Results

Test Conditions - WEP encryption: DISABLED - Tx Rate: Automatic - Power Save: Disabled - Test Partner: USR5410 CardBus card			Firmware/Driver Versions AP f/w: 1.18 Wireless client driver: WinXP 4.0.40.3 Wireless client f/w: No Info
Test Description	SNR (dB)	Transfer Rate (Mbps)	Response Time (msec)	UDP stream
				Throughput (kbps)	Lost data (%)
Client to AP - Condition 1	0	20.7 [No WEP] 19.9 [w/ WEP]	1 (avg) 2 (max)	499	0
Client to AP - Condition 2	0	20	1 (avg) 2 (max)	499	0
Client to AP - Condition 3	0	15.4	1 (avg) 4 (max)	499	0
Client to AP - Condition 4	0	12.8	2 (avg) 3 (max)	499	0

See details of how we test.