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RF Interference Sources Monitor For an Access Point


The RF Interference Sources monitor for single access points consists of a bar chart that reflects interference experienced with the traffic of one or both radios on the access point selected in the View pane. Some access points have two radios and some access points have one radio. Network Director tracks and monitors radio interference from these sources:

  • Microwave ovens—Most domestic microwave ovens use 2.45 GHz, and can interfere with Wi-Fi channels from 8 to 10 (or even 7 to 11). Interference varies depending on the model of the oven—for example, commercial restaurant microwave ovens sweep over a wider spectrum and have a higher duty cycle.

  • Continuous wave devices continuously transmit at a particular frequency without attempting to share the radio frequency medium with other devices. Devices that use continuous wave technology in the same frequency bands as wireless LAN networks will interfere with wireless communications, reducing performance or totally preventing communication. Several examples of devices that may use continuous wave transmission that interferes with WiFi are video surveillance cameras and baby monitors.

  • Bluetooth devices

  • Phone FHSS from cordless phones

  • Unknown devices

To track these interference devices, Network Director polls the access point’s controller at the standard interval. The categories with the largest bars in the chart cause the most interference.

You can perform the following actions on the bar chart:

  • Change the time period over which to display interference by selecting a time period from the list in the upper right corner.

  • Display a numeric value by mousing over a bar in the chart.

  • Add or remove one or both radio’s data from the chart by clicking Radio 1 or Radio 2 in the legend.

Interference is frequently not a problem on wireless networks with light traffic, but as traffic becomes heavier, throughput and capacity decrease and other problems become apparent. RF interference can cause packet retransmission (see Monitoring the Percentage of RF Packet Retransmissions). Interference is also a security concern because jamming can bring down the network.

Ideally, interference retransmission does not cause more than 10% of the total number of packets sent. If your retransmission percentage is higher, you can try to lower it by:

  • Locating and eliminating offending devices. If the item cannot be removed, you can add electromagnetic interference (EMI) shielding such as grounded mesh, foils, insulating foams, or insulating paint. This will limit the interference to a small area.

  • Moving the affected access point.

  • Moving clients to channels with less interference. Keep in mind, however, that Bluetooth devices, cordless phones, 802.11FH devices, and jamming emissions are broadband, so it's not possible to change channels away from them—they are everywhere in the band. For more information, see Understanding Wireless Radio Channels and Understanding Adaptive Channel Planner.

For more information about wireless interference, see Understanding Wireless Interference .