Cisco 9971 Deployment Manual page 30

When designing the placement of access points, be sure that all key areas have sufficient coverage (signal).
Typical wireless LAN deployments for data only applications do not provide coverage for some areas where VoWLAN service
is necessary such as elevators, stairways, and outside corridors.
Wireless LAN interference is generated by microwave ovens, 2.4 GHz cordless phones, Bluetooth devices, or other electronic
equipment operating in the 2.4 GHz band.
Microwave ovens operate on 2450 MHz, which is between channels 8 and 9 of 802.11b/g. Some microwaves are shielded more
than others and that shielding reduces the spread of the energy. Microwave energy can impact channel 11, and some
microwaves can affect the entire frequency range (channels 1 through 11). To avoid microwave interference, select channel 1
for use with access points that are located near microwaves.
Most microwave ovens, Bluetooth, and frequency hopping devices do not have the same effect on the 5 GHz frequency. The
802.11a technology provides more non-overlapping channels and typically lower initial RF utilization. For voice deployments,
it is suggested to use 802.11a for voice and use 802.11b/g for data.
However there are products that also utilize the non-licensed 5 GHz frequency (e.g. 5.8 GHz cordless phones, which can impact
UNII-3 channels).
Cisco Unified IP Phone 9971 Wireless LAN Deployment Guide
30