3. Speed Limit 70Mbps

Figure 2 shows the test setup that GlobespanVirata had in its hotel room. Please excuse the quality of the picture, as I'm still getting used to using my new mini digital camera, which lacks auto-focus.

Figure 2: Nitro XM test setup

On the left is a two laptop setup using two NETGEAR WG511T 108Mbps Cardbus cards and WGT624 108Mbps router, both of which are based on Atheros' Super-G technology. The right side has two laptops using PRISM reference design cards running through a PRISM reference design router, all of which were Nitro XM-enabled.

Figure 3: Nitro XM Test Result

Figure 3 shows the results of a LAN Mark XT throughput run, using a highly compressible data file (A-Z, 0-9 repeated multiple times). The results show that Nitro XM really can produce the claimed 70Mbps throughput, without the channel bonding that has made Atheros' Super-G the bad boy of throughput enhancement technologies. (The two lines in the graph are receive and transmit throughput and the Y axis scale is 10Mbps per line.)

To see if the Super-G WLAN was able to play as nicely with Nitro XM as it did with other PRISM-based products, I asked the demo master to run both the Super-G and XM setups at the same time.

Figure 4: Nitro XM with Super-G running

Figure 4 fuzzily shows (the vertical scale is the same in Figure 3) that although the Nitro XM network showed significant throughput variation, the Super-G network didn't come anywhere near shutting it down. I also took a screen shot of what happened to the Super-G network, but it really didn't come out. But the result was that the Super-G network showed similar throughput variation due to interference from the Nitro XM network, but again, no network shutdown.

These results might seem to contradict GlobespanVirata's claim that Nitro XM "does not cause interference to other networks in the area". But as I showed in the Atheros Super-G NeedToKnow, any two wireless networks placed as closely as the two in this setup will interfere with each other, no matter what flavor they are.

The other "factoid" I learned was that XM has UDP optimization built in. This is a good thing since multimedia streams are UDP based. I saw a quick animated-block demo that showed throughput over 200Mbps with Nitro XM vs. about 40Mbps when run on the SuperG setup.

That's all for Nitro XM. Next I'll next take a look at what Broadcom's Afterburner has to offer.