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Clear Choice Test

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Analyze this: Low-cost wireless spectrum analyzers do the trick

Cisco, Fluke and AirMagnet -- all rooted in Cognio code -- are top performers

By , Network World
March 23, 2009 12:03 AM ET

Network World - While it's seldom necessary (post-installation, anyway) to test the physical-layer behavior of a wired LAN infrastructure, the same cannot be said for wireless LANs.

How we tested the WLAN spectrum analyzers
Archive of Network World tests
Standalone spectrum analyzers' days might be numbered
Wireless router basics

Many elements, including fading, antenna orientation and traffic congestion, can impact the quality of a given connection on a moment-to-moment basis. And there's always the possibility that external sources of interference, many unrelated to Wi-Fi but otherwise sharing the unlicensed bands in which Wi-Fi devices operate, will cause PHY-layer problems ranging from difficult-to-evaluate transient performance hits to an outright disruption of communications.

But fear not: just as it's possible to analyze IP at Layer 3 and Wi-Fi protocols at Layer 2 (see our test of Wi-Fi capture and analysis tools), it's also possible to capture, visualize and analyze the energy present at Layer 1 thereby identifying, characterizing and even localizing sources of interference.

And, as this Clear Choice test proves, you can do all that without having to drop $20,000 on a spectrum analyzer intended for design and manufacturing engineers and otherwise required for use in commercial troubleshooting applications until just a few years ago.

In this test, we looked at seven products designed for WLAN spectral analysis in enterprise environments. Those (three, in fact) based on Cisco's Spectrum Expert came out on top (Cisco sells it's own version while Fluke and AirMagnet built their products on an OEMed technology from Cognio, which Cisco bought in 2007), with an excellent combination of functionality, performance and ease-of-use at a price that won't put much of a dent in ever-tightening IT budgets.

With the tools from these three vendors, we found it simple and intuitive to evaluate, identify and otherwise interpret traffic in both the 2.4 and 5 GHz. bands. But, to be fair, all of the products we looked at addressed the challenge with differing degrees of functionality and ease, and a couple of those pull that off at bargain basement prices.

We highly recommend that enterprise WLAN installations of all sizes have access to a spectral-analysis tool, both for pre-installation RF sweeps and post-installation troubleshooting when interference is suspected.

Categorizing spectrum analyzers

Spectrum analysis usually requires hardware that is separate from a radio designed for communications, because radio chips designed for Wi-Fi are almost always dedicated to networking and are seldom capable of serving as wideband receivers. A receiver in a spectral analysis application must be able to capture energy independent of protocol, making its services quite complementary to both wireless networking and the capabilities of multi-function Wi-Fi assurance tools, such as those from AirMagnet and WildPackets.

All of the products we tested are hosted on Windows-based notebooks and handhelds with add-on sensor radios and software. The radios used for spectral capture range from older non-Wi-Fi frequency-hoppers to custom-designed sensors embedded in PC cards, USB dongles or larger packages attached to a mobile PC or handheld.

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