Fast Transition (FT), also known as IEEE 802.11r, is the key-caching mechanism that must be configured to speed up the reauthentication delays on the wireless infrastructure. FT allows for rapid re-authentication when roaming between access points, reducing the time required for re-establishing security keys and thus speeding up the overall process2.
CCNP Enterprise Wireless Design ENWLSD 300-425 and Implementation ENWLSI 300-430 Official Cert Guide Premium Edition and Practice.

Section: Wired and Wireless Infrastructure

In a Cisco wireless network, when designing for client roaming between access points (APs) that are connected to different controllers, especially in a global enterprise with multiple data centers, it is essential to ensure seamless client mobility. Mobility lists are used in such scenarios to define which controllers are allowed to participate in client roaming. This feature allows the APs connected to controllers within one group (e.g., Group ABC) to recognize and facilitate roaming clients from another group (e.g., Group XYZ). The mobility list is configured on each controller and includes the IP addresses of other controllers that should be considered part of the same mobility domain. When a client roams from an AP on one controller to an AP on another controller, if both controllers are in each other's mobility list, they will establish a mobility tunnel through which they exchange the client's context and security credentials. This ensures that the client can roam without re-authentication and maintains session continuity.
References:
* CCNP Enterprise Wireless Design ENWLSD 300-425 and Implementation ENWLSI 300-430 Official Cert Guide Premium Edition and Practice Test.
* Designing Cisco Enterprise Wireless Networks (ENWLSD) course and training videos available on Cisco Learning Network and Cisco official website.

Explanation

https://www.cisco.com/c/en/us/td/docs/net_mgmt/prime/infrastructure/34/user/guide/bk_CiscoPrimeInfrastructur minimum is -90 and maximum is -67 for IP phone