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Doing more with spectrum analysis: Cisco CleanAir

Wireless engineers have had spectrum analysis in their toolboxes for a long time, but the CleanAir solution from Cisco integrates the tool directly into the WLAN infrastructure. Network administrators who deploy this enhanced level of spectrum intelligence and automation should understand its limitations and prepare for the surprises they find when they turn on CleanAir.

Wireless network engineers have traditionally used spectrum analyzers as spot troubleshooting tools, but enterprise wireless LAN vendors have recognized that spectrum analysis has much greater potential when it is incorporated into the WLAN infrastructure. Spectrum analysis has the potential to create self-healing WLANs that can automatically detect, identify and remediate sources of interference. With an eye toward enabling an all-wireless enterprise, Cisco Systems has launched arguably the most ambitious of these efforts: the CleanAir solution.

CleanAir joins a growing field of enterprise WLAN solutions to offer spectrum analysis tools within the architecture. A common approach is to leverage spectrum analysis capabilities already built into the chipsets of the wireless radios to enable network administrators to remotely visualize the activity in the airspace around the access point as they would otherwise do by taking a laptop to the area. This way an administrator can take a radio offline to troubleshoot a problem without leaving the confines of his desk. Alternatively, a number of infrastructure and third-party vendors allow enterprises to overlay a separate network of wireless sensors, which are typically access points with custom firmware for dedicated sensor duty, to scan the environment and report their results to a separate management software solution. CleanAir takes a third approach, making spectrum analysis an integral, always-on component of the infrastructure and making the results of that analysis actionable.


CleanAir is based on technology from Cognio, the spectrum analysis firm Cisco acquired in 2007. With CleanAir, Cisco has integrated the same level of interference detection and identification available in Cognio’s Spectrum Expert software into its unified wireless network. To accomplish this, Cisco launched a new line of access points, the Cisco Aironet 3500 series, with a custom ASIC chipset that collects spectrum analysis data. These access points have two distinct modes of spectrum analysis. The first allows the access point to service wireless clients while also performing spectrum analysis on the same WiFi channel. Alternatively, engineers can configure an access point for dedicated sensor duty. The AP will poll each of the standard channels for interferers, but it will not handle client access.

Likewise, to achieve the full capabilities of CleanAir, including location and historical data about interference issues, enterprises need more than just the latest access points. While Cisco’s Wireless Control System (WCS) manages the CleanAir-capable access points, the solution also integrates with Cisco’s Mobility Services Engine (MSE) to collect location data and build a history of the spectrum intelligence data collected by the access points. Cisco designed MSE’s location database to track wireless devices based on MAC address, enabling administrators to watch a device move through any of their wireless networks from a centralized depository. For non-WiFi devices that CleanAir detects as interferers, such as cordless phones or wireless video cameras, CleanAir assigns pseudo-MAC address based on the interferer's unique wireless signature. These unique identifiers enable administrators to track an interfering device, even if it moves between access points or facilities.

CleanAir also has an event-driven radio resource management (RRM) feature. In a pure CleanAir deployment, with all access points in the facility being CleanAir compatible, the solution can not only determine when interference is impacting users, but actively change channels on affected access points to automatically remediate around the source of interference. While this could cause some co-channel interference, with the possibility for access points near each other to be in conflict on the same WiFi channel, many engineers will consider a small amount of contention a fair trade for dealing with larger sources of interference. To enable this level of automation, Cisco gives a number value, known as an air quality score, to each section of the wireless network. Enterprises can configure the wireless management system to take action if the air quality score falls below an acceptable level, either by, notifying support staff or automatically remediating the problem. Unfortunately, the enhanced RRM capabilities are only available on CleanAir capable access points, nixing the possibility of deploying the Aironet 3500 series as sensors within a network of older Cisco 802.11n access points. Enterprises, especially the early adopters of 802.11n access points, are faced with a difficult choice: automated remediation can be achieved, but only by significantly upgrading wireless hardware with new compatible access points. The alternative is adding CleanAir compatible sensors into the existing wireless, which provides an integrated monitoring and troubleshooting tool, but lacks the automation of a full CleanAir deployment.

University forgoes handheld WLAN spectrum analyzers for integrated CleanAir spectrum analysis

With or without RRM automation, Joe Rogers, a senior network engineer for the University of South Florida (USF), definitely sees value in the CleanAir solution. USF currently has replaced legacy equipment with CleanAir access points in three of its campus facilities and it will continue switching out older access points for CleanAir access points as his budget allows moving forward. “We’re even considering placing some access points as sensors in buildings not yet up for transition. CleanAir, even without the channel changing capabilities, gives us a lot of information [with which] to manage all of our wireless networks.”

According to Rogers, the architecture and site planning for his CleanAir deployment was no different from previous WLAN deployments. “For the new deployments, we architected the placement of access points to provide blanket 5Ghz 802.11n coverage, which is a bit more demanding in our concrete buildings than the more common 2.4Ghz. This also affords us blanket scanning capabilities for CleanAir.”

One thing that Rogers and his team did discover, however, was that interference issues were more significant than they were even aware of. “CleanAir actually created some additional work for us - cleaning up RF messes we didn’t know we had,” noted Rogers, suggesting that anyone considering a CleanAir deployment should build some project time post-deployment to hunt down the sources of interference uncovered by CleanAir.

Ultimately Rogers will replace USF’s existing 2,400 access points to CleanAir-capable devices, particularly in its residence halls. Student dorm rooms are arguably a wireless network administrator’s worst nightmare because students bring a plethora of WiFi and non-WiFi wireless devices, such as wireless controllers for game consoles. These game consoles compete with WLAN infrastructure for airtime on the unlicensed 2.4Ghz spectrum .

As beta testers of Cisco’s CleanAir, Rogers and his team installed CleanAir access points set to sensor mode within the wiring closets of these residence halls to test the system’s scanning capabilities. They were impressed.

“CleanAir was not only able to detect interference from these devices, but specifically identify that it was an Xbox wireless controller. Nailing the identity of the wireless device saves a lot time in trying to find the source.” Rogers said. In the past Rogers would have had to dispatch an engineer to wander the building with a laptop and spectrum analyzer in search of interference that could have disappeared before it were ever found.

This was last published in November 2010

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