6. The Tests - 32 STA Throughput

Once I had the test setup shaken down, I started in on load testing. I first jumped directly to trying the maximum load that the EE could generate - 64 vSTAs - but ran into too many problems, with too many possible causes. So I dropped back to using a 32 STA load, since all the manufacturers said their products could handle at least that many STAs. Note that Linksys said that 32 was the maximum number of STAs that the WAP54G is designed to handle.

I also decided to increase the test run time from 5 minutes to 4 hours for the 32 STA tests. There's nothing magic about 4 hours, I just chose it because it was as good a place to start as any and let me get three to four test runs in per day.

Figure 11: STA to AP throughput - 32 STA - 4 hours

Figure 11 shows that all products made it through the four hour uplink test with results similar to those of the single STA tests. Note again that the 3Com / SMC tests were done with the EE set to autorange its transmit rate, while all other tests were done with the rate forced to 54Mbps.

The throughput numbers in the graph represent the sum of the average throughput measured for 32 vSTAs. The actual per-STA throughputs were, of course, much lower - with averages typically about 1/32 of the total throughput. So for the range of results shown, this means that each STA was putting along at an average rate of at best, slightly over 0.5Mbps and at worst slightly under 0.4Mbps.

The only surprise in the results was the change in the Linksys WAP54G's throughput, which increased from 12.3 in the single STA case to 14.7Mbps! My explanation for this is that the single STA run result was skewed by the WAP54G's high throughput variation and periodic "dropouts" over the shorter 5 minute test. Both these effects were mitigated by the longer test time and lower per-STA average throughput.

Downlink takes some APs Down

The 32 STA test in the AP to STA (downlink) direction pushed some of the APs to their breaking point. Only the Buffalo Tech WLA-G54C and Gigabyte GN-A17GU AP's finished the full four hours with average total throughput of 21.5 and 20Mbps respectively. The run time before first error (I stopped the test after one error from any of the STAs) for the other APs is shown in Figure 12.

Figure 12: AP to STA Test Duration - 32 STA Throughput test

The exact time-before-first-error isn't important, but I found by repeating the test for the failing AP's that the times are indicative of the relative robustness of the products for this test. The zero times for the 3Com / SMC twins indicates that I couldn't even get those products to start the test.