Cisco Cisco Aironet 3500p Access Point Weißbuch

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Persistent device avoidance information can also be shared from Cisco CleanAir enabled access points to

neighboring non-CleanAir enabled access points (assuming all access points are connected to the same

controller).

Finally, access points in monitor mode (or with the Wireless Security Module installed) will also detect and register

persistent devices on all the monitored channels. Information on detected devices is shared with neighboring local

mode access points, preventing these access points from using channels affected by persistent device

interference. In this case, PDA data storage is extended to keep information about devices on all the channels, and

the monitor mode access point is enhanced to register persistent device data.

Event-driven RRM recognizes that some interference events are severe and catastrophic in nature. For example, a

cordless phone with a continuous FM signal can cause an outage of several minutes (as long as the phone is

active). For this reason, a dramatic drop in air quality causes the system to immediately evaluate changing the

channel for the affected access point. Note that if a channel change occurs, it is done only for the impacted access

point, while avoiding any cascading impact to the channel plan of neighboring access points.

Although in many cases the best response to interference is for the administrator to manually move, remove,

replace, or shield the interfering device, automated mitigation is highly desirable to maintain short-term

performance until other actions can be taken. And in certain cases, it may not be possible to ever remove the

source of interference - for example, if it comes from outside the building.

Access Points as Analyzers

Finally, Cisco CleanAir technology continues to offer an expert view of low-level spectrum plots comparable to that

offered by the Spectrum Expert analyzer tool. Any CleanAir access point can be configured as a network-

connected sensor to see the spectrum plots directly as received by the radios on the access point.

While it is true that the system provides a great deal of higher-level analyzed data, including classified devices and

air quality, there will always be cases where it is desirable to look at the raw spectrum data itself in real time. Even

for enterprises that do not have an RF expert on staff, the Spectrum Expert Connect feature, shown in Figure 4,

can be used by an expert who is brought in to help with a particularly difficult-to-diagnose problem.

Figure 4. Using the Spectrum Expert Connect Feature to Diagnose a Problem at an Access Point