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Lab Notes: Wireless Clouds Can Fog Reception

While we were evaluating gateways in the PC World Test Center, we discovered that the performance of a wireless network can be greatly affected by the presence of other wireless networks in the vicinity. Before you install a wireless network, determine which of the 11 channels the other wireless networks in your area use; this may involve asking the people running them or looking up settings in each product's setup program. Make sure your channel is at least three settings up or down from any other channel in use nearby.

The download and upload tests: We conducted both tests via wired and wireless connection. For the wireless test, the client was within 3 feet of the gateway. Our setup emulated a client connecting through the gateway to an ISP, but instead of using an actual ISP, we used another PC acting as a server. That way our bandwidth wasn't limited by the ISP. We measured the maximum throughput of the connection through the gateway by transferring a 50MB file. We used Windows XP's built-in FTP client to transfer the files in both directions. Though all the products had more throughput than is typically available over a broadband connection, the throughput was about half the rated maximum for the gateways, indicating the overhead caused by network address translation and other filtering operations performed on the data going through the gateways.

The ping test: This shows the response time of one packet of data going from the client through the gateway to the server. The test indicates how much the gateway will slow down a connection, by measuring the wait time (or latency) it adds between when the signal is sent and when it is received. There was a little variation here, but all the times were pretty low, which tells us that the gateways don't add much latency.

No WEP vs. 64- and 128-bit WEP: We tested all the gateways with Wireless Encryption Protocol data security enabled at both 64 bits and 128 bits. Some of the units, such as the SMC Barricade Plus, took a big performance hit when we turned on WEP; others weren't affected at all. Most of the units showed no difference between 64- and 128-bit WEP, and those that did had only a tiny difference.

Elliott Kirschling

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