How We Tested - Interoperability

I didn't use the Azimuth system for the interoperability tests, but instead used my interference-free lab area and close-range open-air tests. The routers were placed on a tabletop in the arrangement shown in Figure 1, with the Dell Inspiron 4100 notebook that held the client cards sitting on the same table, about 1-3 feet away from the routers.

I first uninstalled any previously installed wireless card utilities and drivers from the notebook, and ran a Windows System Restore to the point before those cards were installed. I also checked for updated firmware for all routers and installed any that I found. I then proceeded as follows:

• Step 1: Checked for driver updates and installed any that I found, otherwise I ran the CD that came with the client card.
• Step 2: Powered on a router and associated the card (STA) using its client manager utility (except for WPC54G, which used XP Zero Config).
• Step 3: Used IxChariot with the throughput.scr and a file size = 1,000,000 bytes and TCP/IP protocol to simultaneously run one up and one downlink stream for one minute.
• Step 4: When the test was completed, power down the router
• Step 5: Repeat Steps 2 through 4 until the card had been tested with all routers.
• Step 6: Uninstalled the driver and client utility, ran a Windows System Restore to the point before the driver and client utility installation.

Steps 1 through 6 were repeated until all cards had been tested with all routers.

The results are presented in Tables 1 and 2 below (separated only due to page width restrictions), but here are the key take-aways:

• The good news is that all products that I tested were able to detect, associate and successfully transfer data both up and downstream. Beyond that, "mileage" definitely varied.
• Best results were obtained when running each router with its matching card, indicated in the tables by shaded cells.
• Next best speeds were measured when the Netgear and Buffalo products that both use Broadcom's Intensi-fi chipsets, were mixed, which resulted in a throughput reduction of 5 to 8% over matched-set results.
• Many combinations produced unbalanced up and downlink throughput. When speeds were unbalanced, uplink usually dominated, sometimes as much as 3X downlink

The company with the messiest interoperability story is Netgear, since it has chosen to have two draft 11n products using different chipsets, as well as MIMO products using two generations of Airgo MIMO chipsets (which do not claim anything with regard to draft 11n). The short story here is that mixing any of the Netgear products, whether they used Broadcom, Marvell or Airgo chipsets, resulted in un-enhanced 802.11g speeds, i.e. around 20 Mbps best case.

A final note is that the Netgear WN511T client manager utility was particularly badly behaved. I had to reboot my notebook every time I changed wireless routers in order to have the card detect them.

Table 1: Interoperability Matrix - Part 1

Table 2: Interoperability Matrix - Part 2

Tags: 802.11n,

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