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Why spectrum analyzers are still relevant.

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Wireless networks have seen many different trends emerging over the years, probably one of the most prevalent trend is the ability for access points to monitor to the RF spectrum around the access point. Whether you work with Cisco CleanAir, Aerohive, Aruba, or one of the other big wireless vendors they each have their own way of monitoring and reporting the surrounding RF environment. This is definitely a feature that is very useful for viewing the overall health of the wireless spectrum, after all this spectrum is the layer 1 medium for the WLAN and if there is a lot of contention/interference over the RF then the WLAN will see a performance degradation.

One thing I have inadvertently seen this built-in feature do is provide a false sense of security and make people believe they do not have a need to have any other spectrum analysis tool. There is one flaw with relying on this feature, it is the fact that this feature will only provide you a view of the RF surrounding the access point, while your first reaction is going to “well yes it does, that is what it is supposed to do” this feature does not (and will not) provide you with a view of the spectrum from the client’s perspective. Consider a deployment where you do not have access points peppered around an area every 20 feet and instead have access point spread out every 50-80 feet and you hear consistent complaints of wireless issues. The first reaction of any network engineer is going to be check the access point:

  • Is the access point servicing clients
  • Is there a configuration issue
  • How does surrounding RF look
  • What do the wireless statistics look like

Now usually one of those four things will point you in the right direction, but what I find that is pretty common trait is that after reviewing the RF statistics surrounding the access point (and assuming it looks good/normal) no further thought will be given to the layer 1 medium simply because they looked to access point. All the while the client wireless device might be a good 30 ft away behind a few obstacles surrounded by or near a set of interfering devices.  That is where you would want someone on the ground with a spectrum analyzer.

I’m not saying you need to have a spectrum analyzer everywhere you have wireless because we all know in large networks wireless can grow drastically and certain large networks can see thousands of access points across many different offices, but I merely want to point out a flaw in completely relying on a technology that provides RF Spectrum visibility from the access points perspective, because that is all it is.

Written by Stephen J. Occhiogrosso

August 28, 2013 at 11:42 AM

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