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
| Firmware/Driver Versions AP f/w: | ||||
|---|---|---|---|---|---|
| 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 |