Features Help Visualize Interference Issues

By Andrew Garcia  |  Posted 2010-08-12 Print this article Print


Adding a WCS server and an MSE into the mix adds a number of features to help visualize and respond to interference issues in larger networks.  The WCS's CleanAir dashboard offers clean graphical depictions of both the average and minimum AirQuality scores in both bands across the network over the last seven days and raw interferer counts with detailed lists of the worst interferers and their effects, as well as potential security risks. 

The mapping capabilities of the WCS are also extended to CleanAir, with the system attempting to place detected interferers on a floor plan, provided at least three APs detected the source. With an MSE in place, I could also track movements of an interferer over time, provided sources were merged properly.  I typically found location estimates for non-WiFi sources weren't as accurate as those presented for WiFi devices, but, in most cases, the plots on the my map fell within 5-10 meters of the actual source location with a few egregiously wrong outliers. However, since local-mode APs only listen on the transmit channels, I'm not surprised about the inaccuracies, given the lack of points of triangulation in my small test network.  

Perhaps my favorite CleanAir feature is the integration between CleanAir and the new Cisco Spectrum Expert 4.0 software for Windows PCs (price with PC card is $4260, or the software is a free download to use only with CleanAir sensors), called Spectrum Expert Connect. While previous iterations of Spectrum Expert required the network administrator to capture RF information by wandering around with a laptop armed with the software and a spectrum analysis PC Card sensor, version 4.0 lets administrators sit at a desk and use as the sensor a 3500-series AP deployed anywhere in the network. 

Connected remotely to the AP in this way, an administrator gains access to the raw spectrum analysis data that CleanAir works so hard to simplify and qualify. Through Spectrum Expert Connect, the administrator gains access to the real time Fast Fourier Transforms, Duty Cycle graphs and Swept Spectrograms, as well as visualizations of channel utilization, interference power, and channel utilization versus time.  Spectrum Expert also provides good analysis of the RF characteristics of detected interferers.

Unfortunately, the massive tradeoff with this feature is that the AP must be taken offline and rebooted to run new code by placing it in Spectrum Expert Connect mode from the WLC or the WCS. The AP cannot service clients nor perform regular WiFi scanning while in this mode, potentially leaving a hole in one type of coverage or the other. The disappointment is doubled, then, because I could only view a single bands' RF detail at one time, leaving the other radio in the SE-Connect-mode AP only able to report CleanAir IDRs and AirQuality back to the controller. 

Down the road, I suspect Cisco will find a way to let administrators use SE Connect to attach to local mode access points as well, to at least be able to analyze the RF details for the channel in each band on which the AP is transmitting.

Andrew cut his teeth as a systems administrator at the University of California, learning the ins and outs of server migration, Windows desktop management, Unix and Novell administration. After a tour of duty as a team leader for PC Magazine's Labs, Andrew turned to system integration - providing network, server, and desktop consulting services for small businesses throughout the Bay Area. With eWEEK Labs since 2003, Andrew concentrates on wireless networking technologies while moonlighting with Microsoft Windows, mobile devices and management, and unified communications. He produces product reviews, technology analysis and opinion pieces for eWEEK.com, eWEEK magazine, and the Labs' Release Notes blog. Follow Andrew on Twitter at andrewrgarcia, or reach him by email at agarcia@eweek.com.

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