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
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.
All of these products use software clients to analyze and display raw data and results. The biggest issue we found with most of these products lies in the sampling rate supported. Whereas a high-end spectrum analyzer will be able to display the energy in a large swath of spectrum in real time, these products sweep across the spectrum of interest usually at about a 1-Hz. rate.
Thus it may take a few minutes to gather enough data to give you a good look at what's happening in a given chunk of spectrum. And it's thus good practice to let an analyzer run for a while before attempting to interpret or analyze measurements, and to rely on heatmaps and other data of a cumulative nature rather than instantaneous readings for most decisions.
That said, all of the tools tested can do a credible job at evaluating spectral usage and in identifying potential sources of interference, the most common applications of spectral analysis in enterprise and related commercial settings.
The descendents of Cognio
Since it acquired low-cost spectrum analysis pioneer Cognio in 2007, Cisco has continued to sell Cognio's flagship application, Spectrum Expert. Bundled with a PC card sensor capable of covering the 2.4 and 5 GHz. unlicensed bands, Spectrum Expert was the first PC-based spectrum analysis product to challenge traditional (and expensive) spectrum analyzers. Cognio established OEM agreements with a number of firms, and AirMagnet and Fluke Networks continue selling versions of Spectrum Expert under those agreements today. We tested all three products, and, as might be expected, they are essentially identical in features (with the exception of Cisco's Wireless Control System (WCS) integration feature, replaced by a simple SNMP gateway in the other two) and performance.
It's important to note that these three products did not always yield the same results, however. Given variations in antennas and physical position, simultaneous measurements did in fact vary. But using these tools in a production environment doesn't call for precise dB-accurate measurements - rather, what's needed is the ability to detect, categorize and localize interference, and all three of these products are excellent in those regards.
And the winner is…
All of the products tested could serve the needs of enterprise network planners, for pre-installation RF sweeps, and network operations staff for troubleshooting and ongoing analysis. All discovered the devices we set out as interferers (access points, cordless phones and a microwave oven), with varying reports of specific signal strength. We were pleased to discover that the continuous video stream usually on in the office generated surprisingly little traffic, and thus interference, to others on Wi-Fi Channel 11.
But picking a winner here is tough because of the large range of prices and capabilities represented in the products tested. If we had to pick just one, though, we'd go with Cisco's Spectrum Expert. It's robust, flexible and useable by those with little background in traditional spectrum analysis - in other words, by enterprise installation and support staff. AirMagnet users might want to purchase its version of this product, as it integrates with other AirMagnet tools. Fluke Networks also provides a number of implementations of this functionality, including a standalone wireless version of their EtherScope Series II Network Assistant. At any rate, the functionality in the Cognio descendents is rich and makes spectral analysis a breeze in enterprise settings.
But it's fair to point out that the entry price for all of the above is above $4,000, including a PC, so that may direct some users to the two low-end tools reviewed here. Both are quite useable, but the responsiveness, 5 GHz. coverage, and interference analysis tools in the Metageeks product gives it the nod. They also have a 2.4 GHz.-only product (Wi-Spy 2.4x) that sells for $399.
The BVS products will appeal to those who need spectral-analysis functionality every day. They're designed for continuous (and even outdoor) duty, and these products are rugged, calibrated test equipment. The range of function and ease of use, however, was somewhat disappointing. While the price of the Yellowjacket is fairly high relative to the others tested here, keep in mind that a PC of some form is also required for the other tools. The out-of-the-box, ready-to-go nature of the Bumblebee and the Yellowjacket will be attractive to many - but an update in user interface, especially for the Yellowjacket, should be in the works here.
Mathias is a principal with Farpoint Group, an advisory firm specializing in wireless networking and mobile communications. His blog, Nearpoints, resides at Network World. He can be reached at firstname.lastname@example.org.
Mathias is also a member of the Network World Lab Alliance, a cooperative of the premier reviewers in the network industry each bringing to bear years of practical experience on every review. For more Lab Alliance information, including what it takes to become a member, go to www.networkworld.com/alliance.