November 10, 2010, 1:50 PM — There's a long-standing need in wired networks to verify the quality of connectivity of wire, cable, and fiber with appropriate test equipment. But with wireless networks, this requirement extends beyond initial site surveys and occasional troubleshooting.
Managers of wireless networks have an ongoing need for spectral analysis, viewing not just protocol-based traffic but also energy in a given band. And this monitoring needs to be constant, because interference, can appear at any time.
At Farpoint Group, we refer to the analysis of energy at the physical layer to improve performance as spectral assurance. With the announcement of Cisco's CleanAir technology, which includes access points with spectral sensing as well as new management software features, spectral assurance is for the first time available as an integral part of the wireless LAN infrastructure.
We call this style of spectral analysis the centralized infrastructure model (CIM), differentiating it from the earlier but still-useful walking around model (WAM) typically implemented on notebook computers.
But instead of having to send out a trained engineer to detect, classify, localize and (perhaps) remedy a given interference challenge, all this can now be done continually and from a central location. So, in addition to getting round-the-clock coverage, the CIM strategy can help lower WLAN operating expense.
We tested CleanAir's functionality in four key areas:
1. Detection - identifying interferers and examining the duty cycle and intensity of their energy.
2. Classification - identifying a specific interferer by its electromagnetic signature. This enabled us to look for specific types of devices as we proceeded further through these steps.
3. Localization - via the power of a CIM-based installation to determine the location of the interferer, a new application of the location and tracking capabilities already present in many WLAN implementations.
4. Remediation - Eliminating the interferer, usually via automatically reconfiguring channel assignments. Localization can also be used to find and physically disable an interferer.
Our test configuration consisted of a Cisco 5500-series WLAN controller, three Aironet 3500-series access points with CleanAir Technology, an identical 3500 AP operating in "monitor mode,'' and a 3300-series Mobility Services Engine, which is an applications server used to perform location calculations.