Cisco 9971 Deployment Manual page 58

The SSID to be used by the Cisco Unified IP Phone 9971 can be configured to only apply to a certain 802.11 radio type.
It is recommended to have the Cisco Unified IP Phone 9971 operate on the 5 GHz band due to have many channels available
and not as many interferers as the 2.4 GHz band has.
Ensure that the selected SSID is not utilized by any other wireless LANs as that could lead to failures when powering on or
during roaming; especially if a different security type is utilized.
In order to utilize CCKM, enable WPA2 policy with AES encryption and 802.1x + CCKM for authenticated key management
type when the Cisco Unified IP Phone 9971 is running firmware version 9.1(1) or later in order to enable fast secure roaming.
Cisco Unified IP Phone 9971 Wireless LAN Deployment Guide
58